U.S. patent application number 13/215459 was filed with the patent office on 2011-12-15 for label switching type of packet forwarding apparatus.
This patent application is currently assigned to HITACHI, LTD.. Invention is credited to Kazuho MIKI, Kenichi SAKAMOTO, Koji WAKAYAMA.
Application Number | 20110305242 13/215459 |
Document ID | / |
Family ID | 18668343 |
Filed Date | 2011-12-15 |
United States Patent
Application |
20110305242 |
Kind Code |
A1 |
MIKI; Kazuho ; et
al. |
December 15, 2011 |
LABEL SWITCHING TYPE OF PACKET FORWARDING APPARATUS
Abstract
A label switching type packet forwarding apparatus having a
routing information table in which a forwarding type of a reception
packet, output port identification information, and output routing
information of a specific layer in the OSI reference model
determined by the forwarding type are defined in correspondence
with routing information which is found upon reception of a packet,
for converting a header of a reception packet in accordance with
the packet forwarding type and the output routing information
obtained by a table search.
Inventors: |
MIKI; Kazuho; (Kokubunji,
JP) ; SAKAMOTO; Kenichi; (Tokyo, JP) ;
WAKAYAMA; Koji; (Kokubunji, JP) |
Assignee: |
HITACHI, LTD.
Tokyo
JP
|
Family ID: |
18668343 |
Appl. No.: |
13/215459 |
Filed: |
August 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12550945 |
Aug 31, 2009 |
8014420 |
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13215459 |
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10894058 |
Jul 20, 2004 |
7586947 |
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12550945 |
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09629706 |
Jul 31, 2000 |
6771662 |
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10894058 |
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Current U.S.
Class: |
370/392 |
Current CPC
Class: |
H04L 49/3009 20130101;
H04L 49/602 20130101 |
Class at
Publication: |
370/392 |
International
Class: |
H04L 12/56 20060101
H04L012/56 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2000 |
JP |
2000164761 |
Claims
1. A packet transmission apparatus for transmitting and receiving
packets comprising: a plurality of input ports for receiving input
packets; a plurality of output ports for transmitting output
packets; a processing unit which performs a header converting
process on an input packet received from one of the input ports in
accordance with output routing information pre-defined for the
input packet, and outputs a header converted packet to one of the
output ports specified by an output port identifier pre-defined in
association with the output routing information, wherein the output
routing information includes values of a plurality of output header
information items.
2. The packet transmission apparatus according to claim 1, wherein
the values of the plurality of output header information items
included in the output routing information include a value of a
Multi Protocol Label Switching (MPLS) header and a value of a
Virtual Private Network (VPN) header.
3. The packet transmission apparatus according to claim 1, further
comprising a routing information table including a plurality of
table entries each of which defines the output routing information
and the output port identifier in association with an identifier of
one of the input ports and at least one header information item of
the input packet to be received from the input port.
4. A packet forwarding method performed by a packet transmission
apparatus having a plurality of input ports and output ports each
connected to one of a plurality of communication lines, the method
comprising the steps of: receiving an input packet by one of the
input ports; performing a header converting process on the input
packet in accordance with output routing information pre-defined
for the input packet, the output routing information including
values of a plurality of output header information items; and
outputting the header converted packet to one of the output ports
specified by an output port identifier pre-defined in association
with the output routing information.
5. The packet forwarding method according to claim 4, wherein the
values of the plurality of output header information items included
in the output routing information include a value of a Multi
Protocol Label Switching (MPLS) header and a value of a Virtual
Private Network (VPN) header.
6. The packet forwarding method according to claim 1, wherein the
output routing information and the output port identifier are
retrieved from a routing information table including a plurality of
table entries each of which defines the output routing information
and the output port identifier in association with an identifier of
one of the input ports and at least one header information item of
the input packet to be received from the input port.
Description
[0001] The present application is a continuation application of
U.S. Ser. No. 12/550,945, filed Aug. 31, 2009, which is a
continuation of application Ser. No. 10/894,058, filed Jul. 20,
2004 (now U.S. Pat. No. 7,586,947), which is a continuation of
application Ser. No. 09/629,706, flied Jul. 31, 2000 (now U.S. Pat.
No. 6,771,662), the contents of all of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention relates to a node applied to an IP
(Internet Protocol) network and, more particularly, to a label
switch type packet forwarding apparatus.
[0004] (2) Description of the Related Art
[0005] On an IP network typified by the Internet, data is forwarded
in accordance with the IP protocol. In recent years, attention is
paid to a label switching type packet forwarding for labeling an IP
packet and forwarding a reception packet in accordance with the
label. A typical example of label switching is MPLS (Multi Protocol
Label Switching) which is being standardized by the IETF (Internet
Engineering Task Force).
[0006] In order to make the Invention understood easily, a
conventional technique related to the invention will be described
herein below with reference to drawings.
[0007] FIG. 20 shows an IP network comprising a plurality of
routers R51 to R66 for forwarding IP packets.
[0008] Hosts IP51 to IP55 such as terminals or servers as sources
or destinations of IP packets are connected to the IP network via
the routers. In the IP network shown in the diagram, the router R53
for connecting the routers R51, R52, R54 and R55 has, for example,
a routing information table 100 shown in FIG. 21 to determine the
forwarding route of a reception packet.
[0009] The routing information table 100 comprises a plurality of
entries showing the relation among a destination IP address IN51 as
input information IN5, a next hop router address IM51 as
intermediate information IM5, and output port identifier (output
port number) OUT51 and output layer 2 (L2) information OUT52 as
output information OUT5.
[0010] In the IP network of FIG. 20, for example, when a route of
an IP packet transmitted from the host IP51 to the host IP53 is
RT51 and a route of an IP packet transmitted from the host IP52 to
the host IP54 is RT52, entries EN51 and EN52 having the contents
shown in FIG. 21 are set in the routing information table 100 of
the router R53 in correspondence with the routes.
[0011] For example, when attention is paid to the route RT51, an IP
packet inputted from the host IP51 via the router R51 to the router
R53 has an IP header H1 of a format shown in FIG. 22, in which the
address of the host IP53 is set as an destination IP address H13.
When the IP packet is received from the router R51, the router R53
extracts the destination IP address from the IP header H1 and
searches the table 100 by using the destination IP address as input
information. By the search, an output port number #53 to which the
IP packet is to be forwarded and output L2 information 5i to be
added to an output packet are obtained.
[0012] When the routing information table 100 is divided into a
first table in which the relation between the input information IN5
and the intermediate information IM5 is defined and a second table
in which the relation between the intermediate information IM5 and
the output information OUT5 is defined, by referring to the second
table on the basis of the next hop router address R54 obtained from
the first table, the output port #53 and the output L2 information
5i are obtained. When the input information IN5 and the output
information OUT5 are directly associated with each other on the
same table, the intermediate information IM5 can be omitted.
[0013] The output L2 information added to the output packet denotes
routing information of the layer 2 (data link layer) of the OSI
reference model applied to output lines of the router R53. For
example, when the output line is of Ethernet, an MAC destination
address H21 in an Ethernet header H2 shown in FIG. 23 corresponds
to the output L2 information. When the output line is an ATM line,
VPI/VCI H31 in an ATM header H3 shown in FIG. 24 corresponds to the
output L2 information. When the output line is of POS (PPP over
SONET), as shown in FIG. 31, no information of the layer 2 exists
in the POS header. Consequently, in a table entry corresponding to
the POS line in the routing table 100, the output L2 information
OUT52 is blank.
[0014] The router 53 forwards the reception IP packet to the next
hop router R54 in a format that the output L2 information which is
necessary for a lower layer of the OSI standard model applied to
each of the output lines is added. Also on the packet route RT52
having the information of the destination IP address of "IP54", in
a manner similar to the route RT51, an IP packet is forwarded to
the next hop router R55 in accordance with the output information
of the entry EN52 corresponding to the destination IP address set
in the routing information table 100.
[0015] FIG. 25 shows an example of an IP network including label
switching nodes E61 to E63, C61 and C62 for forwarding packets by
the MPLS.
[0016] In the diagram, an ellipse domain D6 in the center of the
network denotes an MPLS domain for forwarding packets by the MPLS.
In the following description, the nodes E61, E62 and E63 disposed
at the incoming and outgoing ports of the MPLS domain D6 will be
called edge nodes and the nodes C61 and C62 disposed on the inside
of the MPLS domain will be called core nodes. The edge nodes E61,
E62 and E63 are connected to routers R61, R62, R63 and R64 for IP
forwarding the packets, respectively, on the outside of the MPLS
domain D6.
[0017] On the inside of the MPLS domain D6, as shown in FIG. 26,
the packet forwarding is performed in an MPLS packet 210 format in
which a Shim header H4 is added to an IP packet 200. Each of the
edge nodes has a table shown in FIGS. 27 and 28 for determining the
forwarding route of a reception packet. FIG. 27 shows an ingress
routing information table 110 which is referred to when the
forwarding route of a packet inputted from the outside of the MPLS
domain D6 into the domain is determined. FIG. 28 shows an egress
routing information table 120 which is referred to when the
forwarding route of a packet outgoing from the inside of the MPLS
domain D6 to the outside is determined.
[0018] The ingress routing information table 110 comprises a
plurality of entries showing the relation between a destination IP
address IN61 as input information IN6i, and an output port OUT61
and an output label OUT62 as output information OUT6i. The output
label OUT62 corresponds to the value of a label H41 included in the
Shim header H4 of the MPLS shown in FIG. 26.
[0019] The egress routing information table 120 comprises a
plurality of entries showing the relation among a destination IP
address IN62 as input information IN6e, a next hop router address
IM61 as intermediate information IM6e, and an output port OUT63 and
output L2 information OUT64 as output information OUT6e. The egress
routing information table 120 basically has a structure similar to
that of the routing information table 100 shown in FIG. 21 which is
referred to in the IP forwarding.
[0020] In the IP network shown in FIG. 25, when it is assumed that
a route of an IP packet transmitted from the host IP61 to the host
IP63 is RT61, a route of an IP packet transmitted from the host
IP62 to the host IP64 is RT62, a route of an IP packet transmitted
from the host IP63 to the host IP61 opposite to the route RT61 is
RT63, and a route of an IP packet transmitted from the host IP64 to
the host IP62 opposite to the route RT62 is RT64, in the ingress
and egress routing information tables 110 and 120 of the edge node
E61, entries EN61, EN62, EN63 and EN64 having the contents shown in
FIGS. 27 and 28 are set in correspondence with the routes.
[0021] When attention is paid to the route RT61, the IP packet
transmitted by the host IP61 to the host IP63 is inputted to the
edge node E61 via the router R61. The edge node E61 searches the
ingress routing information table 120 by using the destination IP
address "IP63" of the reception IP packet as input information and
obtains output port number "#63" and an output label "L61". The
reception IP packet is converted to an MPLS packet to which the
Shim header H4 including the output label "L61" is added and
forwarded to the output line having the output port number "#63".
In the following description, the packet forwarding from the IP
network to the inside of the MPLS domain will be called "MPLS
edge-ingress forwarding". Similarly, the reception IP packet of the
route RT62 is converted to an MPLS packet including an output label
L63 defined by the entry EN62 in the ingress routing information
table 110 and the resultant is MPLS edge-ingress forwarded to the
output line indicated by the output port number #64.
[0022] On the other hand, packets (MPLS packets) received via the
routes RT63 and RT64 are forwarded to the outside of the MPLS
domain D6 by using the egress routing information table 120 shown
in FIG. 28. The packet forwarding from the inside the MPLS domain
to the outside will be called "MPLS edge-egress forwarding". Since
the routing information table 120 has substantially the same
structure as that of the routing information table 100 of FIG. 21
used for the IP forwarding, the detailed description is omitted
here.
[0023] A packet forwarding performed by a core node in the MPLS
domain (hereinbelow, called "MPLS core forwarding") will be
described.
[0024] FIG. 29 shows a network in which an MPLS domain D7 comprises
edge nodes E71 to E74 and a core node C71 and the core node C71
transmits and receives packets on the POS (PPP over SONET)
line.
[0025] In the MPLS core forwarding on the POS line, as shown in
FIG. 31, a PPP header H5 is added to the MPLS packet 210 and the
packet forwarding is performed in the format of a PPP packet 220.
In this case, the core node C71 has a routing information table 130
shown in FIG. 30 for determining the forwarding route of a
reception packet. The routing information table 130 comprises a
plurality of entries each including, as input information IN7, an
input port number IN71 and an input label IN72 and, as output
information OUT7, an output port number OUT71 and an output label
OUT72.
[0026] In the network of FIG. 29, for example, when it is assumed
that the route of an IP packet transmitted from the host IP71 to
the host IP73 is RT71 and a route of an IP packet transmitted from
the host IP72 to the host IP74 is RT72, the routing information
table 130 of the MPLS-POS core node C71 includes, as shown in FIG.
30, entries EN71 and EN72 having contents corresponding to the
routes RT71 and RT72, respectively.
[0027] When attention is paid to the route RT71, an IP packet
transmitted from the host IP71 to the host IP73 is inputted to the
edge node E71 via the router R71 and is converted to an MPLS packet
having the label value of L71. The MPLS packet is forwarded to the
core node C71. The core node C71 which receives the MPLS packet
from an input port of the port number "#71" uses the input port
number "#71" and the value "L71" of the label (input label)
extracted from the Shim header of the reception packet as input
information and searches the routing information table 130. In this
case, the entry EN71 is hit and the output port number "#73" and
the value "L73" of the output label are obtained as output
information. Consequently, the label value of the reception packet
is rewritten from "L71" to "L73" and the resultant packet is
forwarded to the output line of the output port number "#73".
[0028] The packet on the route RT72 transmitted from the host IP72
to the host IP74 is processed in a manner similar to the packet on
the RT71. The processed packet is subjected to the MPLS core
forwarding in accordance with the output information OUT7 in the
table entry EN72.
[0029] In the MPLS-POS core node as described above, different from
the IP forwarding and the MPLS edge forwarding, the routing
information table is searched on the basis of the input port number
and the label value of the Shim header irrespective of the
destination IP address.
[0030] FIG. 32 shows a network in which an MPLS domain D8 includes
edge nodes E81 to E84 and a core node C81, and a packet forwarding
(MPLS-ATM core forwarding) in the MPLS domain D8 is performed in
the ATM.
[0031] In the ATM, as shown in FIG. 34, the IP packet 200 or the
MPLS packet 210 obtained by adding the Shim header H4 and a trailer
to the IP packet is divided into a plurality of data blocks each
having fixed length (48 bytes). Each of the data blocks is
converted to an ATM cell 230 having a cell header H3 of 5 bytes
shown in FIG. 24.
[0032] The core node (MPLS-ATM core node) C81 for forwarding
packets in the ATM has a routing information table 140 shown in
FIG. 33 for determining the forwarding route of a reception packet.
The routing information table 140 comprises a plurality of entries
each including, as input information IN8, input port number IN81
and input VPI/VCI IN82 and, as output information OUT8, output port
number OUT81 and output VPI/VCI OUT82.
[0033] The reason why input/output VPI/VCI is used in place of the
input/output label is that, in the MPLS core forwarding on the ATM
line, a packet set in an ATM payload is not always limited to the
MPLS packet 210 including the Shim header H4. That is, there is a
case such that the conversion from the IP packet 200 to the MPLS
packet 210 is omitted, the IP packet 200 having no label H4 is
converted to ATM cells, and the ATM cells are MPLS core
forwarded.
[0034] In the network of FIG. 32, when it is assumed that a route
of an IP packet transmitted from a host IP81 to a host IP83 is RT81
and a route of an IP packet transmitted from a host IP82 to a host
IP84 is RT82, entries EN81 and EN82 having the contents as shown in
FIG. 33 are set in the routing information table 140 in the
MPLS-ATM core node C81 in correspondence with the routes.
[0035] When attention is paid to the route RT81, an IP packet
transmitted from the host IP81 to the host IP83 is supplied to the
edge node E81 via the router R81 and converted to ATM cells each
having the VPI/VCI value "v81". The ATM cells are inputted to the
input port of the port number #81 of the core node C81.
[0036] By searching the table 140 by using the value of VPI/VCI of
the received ATM cell as input information, the edge node value
"v83" defined as output information in the entry EN81. In the
reception ATM cell, the VPI/VCI value is rewritten in accordance
with the search result and the resultant is forwarded to the output
line having the port number of "#83". Similarly, the transmission
packet on the route RT82 is also converted into ATM cells which are
sent to the MPLS domain D8. Based on the output information defined
in the table entry EN82, the ATM cells are forwarded to the output
line of the port number "#84".
[0037] As described above, different from the node for performing
the MPLS core forwarding between the POS lines, the node for
performing the MPLS core forwarding between the ATM lines operates
like an ATM switch for switching packets on the basis of only the
input port number and the VPI/VCI.
[0038] When the backbone network of the IP network is replaced by
the label switching network, dispersion of a traffic load, increase
in efficiency of forwarding of data in the network by designating a
route, and construction of a virtual private network VPN are
facilitated. As described above, however, since data is forwarded
according to the IP protocol in the IP network and data is
forwarded according to the MPLS protocol in the MPLS network, there
is a large difference in the format of a forwarding packet and a
construction of a routing information table between the two
networks. Consequently, in the case of constructing an IP network
partially having an MPLS domain, an IP router is necessary for the
IP forwarding and the MPLS node is necessary for the MPLS
forwarding.
[0039] Although the MPLS domain includes the edge node and the core
node, the packet forwarding format of the edge node and that of the
core node are different from each other. A dedicated node is
therefore necessary according to each use. Also in the case of
performing the MPLS core forwarding, not only the layer 2 protocol
process but also, for example, the handling of TTL (Time to Live)
to be added to the packet header in the case where the
communication line is the POS line are different from those in the
case where the communication line is the ATM line. Consequently, a
number of kinds of MPLS nodes are required according to the
structures of networks. In the construction of the label switching
network, there are problems such that the costs of nodes are high
and the network control becomes complicated as the number of kinds
of nodes increases.
[0040] In the case of shifting a part of the IP network to the
MPLS, the functions of conventional edge nodes are divided into, as
explained with reference to FIG. 25, the function of forwarding a
packet from the IP network to the inside of the MPLS domain and the
function of forwarding a packet from the inside of the MPLS domain
to the IP network. The function of forwarding a packet between IP
networks (IP forwarding) is not provided. It causes a problem such
that a flexible network in which the scale of the MPLS domain is
gradually expanded while performing the IP forwarding by the edge
nodes of the MPLS cannot be constructed and a huge amount of funds
is necessary for modernization of the network.
[0041] When the MPLS is once constructed by using the lines of a
certain protocol (such as ATM lines) as a base irrespective of the
scale of the MPLS network, it becomes difficult to shift the lines
to low-cost lines of another new protocol (such as POS lines) of
higher forwarding speed.
SUMMARY OF THE INVENTION
[0042] It is an object of the invention to provide a label
switching type packet forwarding apparatus which can be adapted to
a plurality of kinds of communication protocols.
[0043] Another object of the invention is to provide a label
switching type packet forwarding apparatus which has a plurality of
kinds of communication lines of different communication protocols
and can forward packets among the communication lines.
[0044] Further another object of the invention is to provide a
label switching type packet forwarding apparatus which can deal
with a change in communication protocol applied to input/output
lines.
[0045] In order to achieve the objects, a label switching type
packet forwarding apparatus according to the invention is
characterized by using a routing information table in which a
forwarding type of a reception packet, output port identification
information, and output routing information of a specific layer in
the OSI reference model determined by the forwarding type are
defined in correspondence with routing information which is
peculiar to a reception packet and is found upon receipt of the
packet.
[0046] A label switching type packet forwarding apparatus according
to the invention retrieves a table entry corresponding to the
routing information of the reception packet from the routing
information table, performs a header converting process on the
reception packet in accordance with the packet forwarding type and
the output routing information of the specific layer indicated by
the retrieved table entry, and outputs the reception packet to an
output port indicated by the output port identification information
in the specific table entry.
[0047] More specifically, the routing information table comprises,
for example, a table entry corresponding to the destination IP
address of a reception packet. The packet forwarding types include,
for example, packet forwarding between IP networks, packet
forwarding from an IP network to an MPLS network, and packet
forwarding from an MPLS network to an IP network. With the
construction, a packet forwarding apparatus having both the edge
node function and the function of forwarding a packet between IP
networks can be realized. By including packet forwarding between
MPLS networks in the packet forwarding types, a packet forwarding
apparatus having both the edge node function and a core node
function can be realized.
[0048] In a preferred embodiment of the invention, entries of the
routing information table are prepared in correspondence with a
combination of routing information of a plurality of layers in the
OSI reference model, such as a combination of first information
indicative of an input port of a reception packet, second
information indicative of either an MPLS (Multi Protocol Label
Switching) label or the routing information of the layer 2 in the
OSI reference model for the reception packet, and third information
indicative of a destination IP address of the reception packet. In
this case, the routing information table is searched by, for
example, a search at the first stage using at least the first and
second information as search conditions and a search at the second
stage using the third information as a search condition. The search
at the second stage is performed when there is no table entry
matched with the search conditions at the first stage.
[0049] The other objects and features of the invention will become
apparent from the following description of embodiments with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 shows a first embodiment of a network to which a
packet forwarding apparatus of the invention is applied.
[0051] FIG. 2 shows an example of a routing information table 150
of an edge node E11 in FIG. 1.
[0052] FIG. 3 is a block diagram showing an embodiment of a packet
forwarding apparatus 10 of the invention.
[0053] FIG. 4 is an example of a packet format used in the packet
forwarding apparatus 10.
[0054] FIG. 5 shows an example of a format of an internal header
H6.
[0055] FIG. 6 shows a detailed structure of an input line interface
board 13 illustrated in FIG. 3.
[0056] FIG. 7 is a flowchart showing the function of a layer-2
processing unit 32 illustrated in FIG. 6.
[0057] FIG. 8 is a flowchart showing the function of a multi-layer
processing unit 21 illustrated in FIG. 6.
[0058] FIG. 9 is a flowchart showing the function of a routing
information retrieval unit 23 illustrated in FIG. 6.
[0059] FIG. 10 shows a detailed structure of an output line
interface board 14 illustrated in FIG. 3.
[0060] FIG. 11 is a flowchart showing the function of a multi-layer
processing unit 42 illustrated in FIG. 10.
[0061] FIG. 12 is a flowchart showing the function of a layer-2
processing unit 52 illustrated in FIG. 10.
[0062] FIG. 13 shows a second embodiment of a network to which the
packet forwarding apparatus of the invention is applied.
[0063] FIG. 14 shows an example of a routing information table 160
of an edge node E21 in FIG. 13.
[0064] FIG. 15 shows a third embodiment of a network to which the
packet forwarding apparatus of the invention is applied.
[0065] FIG. 16 shows an example of a routing information table 170
of an edge node E11 in FIG. 15.
[0066] FIG. 17 shows a fourth embodiment of a network to which the
packet forwarding apparatus of the invention is applied.
[0067] FIG. 18 shows an example of a routing information table 180
of a core node E43 in FIG. 17.
[0068] FIG. 19 is a flowchart showing the function of a multi-layer
processing unit 42 in the core node E43.
[0069] FIG. 20 shows an example of a conventional IP network having
a plurality of routers.
[0070] FIG. 21 shows the construction of a routing information
table 100 of a router R54 illustrated in FIG. 20.
[0071] FIG. 22 shows a format of an IP packet header.
[0072] FIG. 23 shows a format of an Ethernet header.
[0073] FIG. 24 shows a format of an ATM cell header.
[0074] FIG. 25 shows an example a conventional IP network including
a label switching type edge node E61 and a core node.
[0075] FIG. 26 shows a format of an MPLS packet forwarded within
the MPLS domain.
[0076] FIG. 27 shows an ingress routing information table of the
edge node E61 illustrated in FIG. 25.
[0077] FIG. 28 shows an egress routing information table of the
edge node E61 illustrated in FIG. 25.
[0078] FIG. 29 shows an example of a conventional IP network
including a label switching type core node C71 connected to another
node via a POS line.
[0079] FIG. 30 shows a routing information table 130 of a core node
C71 illustrated in FIG. 29.
[0080] FIG. 31 shows an example of an MPLS packet format on the POS
line.
[0081] FIG. 32 shows an example of a conventional IP network
including a label switching type core node C81 connected to another
node via an ATM line.
[0082] FIG. 33 shows a routing information table 140 of a core node
C81 illustrated in FIG. 32.
[0083] FIG. 34 shows the relation among an IP packet 200, an MPLS
packet 210 and an ATM cell 230.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0084] FIG. 1 shows an example of a network to which a packet
forwarding apparatus (MPLS node) of the invention is applied.
[0085] In FIG. 1, a region of an ellipse shape in the center is an
MPLS domain D1 for forwarding data in accordance with the MPLS. The
MPLS domain D1 comprises: edge nodes E (E11, E12 and E13) as
incoming/outgoing ports of the domain; and core nodes C (C11 and
C12) for MPLS core forwarding data within the domain. The edge
nodes E are connected to routers R (R11 to R14) of an IP network on
the outside of the MPLS domain D1. In the embodiment, each of the
edge nodes E has not only the IP forwarding function of forwarding
a packet received from one of the routers connected to the node to
another router connected to the node and the MPLS edge forwarding
function of forwarding a packet between the IP network (router) and
the MPLS domain D1 but also the MPLS core forwarding function of
forwarding a packet received from one node to another node in the
MPLS domain D1. By paying attention to the edge node E11, the
features of the invention will be described hereinbelow.
[0086] In order to determine the routing of forwarding a reception
packet, the edge node E11 has, for example, a routing information
table 150 shown in FIG. 2. In the routing information table 150, a
plurality of table entries EN101, EN102, . . . each comprising of
input information IN1 and output information OUT1 are registered.
The input information IN1 as a table search key includes routing
information of a plurality of layers of the OSI reference model. In
the embodiment, the input information IN1 includes input port
number of a reception packet as routing information IN11 of layer
1, label information of a reception MPLS packet as routing
information (input L2 identifier) IN12 of layer 2, and a
destination IP address of a reception packet as routing information
IN13 of layer 2. The output information OUT1 as a table search
result includes: forwarding type OUT11 of a packet; output port
number OUT12 to which the reception packet is to be forwarded; and
output layer 2 (L2) identifier OUT13 indicative of routing
information to be added to an output packet.
[0087] The type of header information designated by the output L2
identifier OUT13 varies according to the forwarding type OUT11 of a
packet. In the embodiment, the forwarding type OUT11 indicates one
of IP forwarding, MPLS edge-ingress forwarding, MPLS edge-egress
forwarding, and MPLS core forwarding (POS-POS). The MPLS
edge-ingress forwarding denotes forwarding of a reception packet
from the IP network to another node in the MPLS domain. The MPLS
edge-egress forwarding denotes forwarding of a reception packet
from another node in the MPLS domain to the IP network side.
[0088] One of the features of the embodiment is that the routing
information table 150 is common to a table for IP forwarding of a
reception packet (reception data) (entry EN103), a table for MPLS
edge-ingress forwarding (entry EN101), a table for MPLS edge-egress
forwarding (entry EN102), and a table for MPLS core forwarding
(POS-POS) (entry EN104), and each of the table entries defines the
packet forwarding type and header information (output L2
identifier) according to the packet forwarding type.
[0089] For example, when the packet forwarding type OUT11 indicates
the MPLS edge-ingress forwarding and the MPLS core forwarding, the
output L2 identifier OUT13 indicates the value of a label (output
label) to be added to the header of the output MPLS packet. The
output label differs according to the protocol of a lower layer
applied to the output line on the MPLS domain side of the edge node
E11. For example, when the output line is of POS or Ethernet, the
output label corresponds to a label H41 in the Shim header format
of the MPLS shown in FIG. 29. When the output line is of ATM, the
output label corresponds to VPI/VCI H31 in the ATM header format
shown in FIG. 27.
[0090] When the packet forwarding type OUT11 indicates the IP
forwarding and the MPLS edge-egress forwarding, the output L2
identifier OUT13 shows routing information of layer 2 (output L2
information) to be added to the output IP packet. The output L2
information differs according to the protocol of a lower layer
applied to the output line. For example, when the output line is of
Ethernet, the output L2 information corresponds to an MAC
destination address H21 in the Ethernet header format shown in FIG.
25. When the output line is of the ATM, the output L2 information
corresponds to VPI/VCI H31 in the ATM header format shown in FIG.
26. When the output line is of the POS, since there is no
identifier corresponding to the POS, the column of the output L2
information OUT11 is blank.
[0091] In the embodiment, the MPLS protocol is classified as layer
2 for convenience since the IP protocol which is in the layer 3 of
the OSI reference model is treated as a reference in the IP network
field and the MPLS lower than the IP protocol is considered to be
in the layer 2. As the MPLS is positioned higher than Ethernet and
PPP defined as in the layer 2 in the OSI reference model, it is
proper that the MPLS protocol is in the layer 2.5 which is between
the layer 2 and the layer 3. In the embodiment, therefore, the
input L2 identifier IN12 and the output L2 identifier OUT13 in the
routing information table 150 denote routing information of the
layer 2 to be added to the forwarding packet on the IP network or
routing information of the layer 2.5 to be added to the forwarding
packet on the MPLS network.
[0092] In the network construction of FIG. 1, when it is defined
that a route of an IP packet transmitted from a host IP11 to a host
IP13 is RT11, a route of an IP packet transmitted from the IP13 to
the host IP11 opposite to the route RT11 is RT12, a route of an IP
packet transmitted from the host IP11 to the host IP12 is RT13, and
a route of an IP packet transmitted from a host IP14 to the host
IP13 is RT14, each of table entries EN101 to EN104 corresponding to
the routes RT11 to RT14 has the input and output information IN1
and OUT1 of the contents shown in FIG. 2. An input item of which
value is shown in parenthesis in the routing information table 150
denotes a "don't care value" such that whatever the value given as
a search key is, the value satisfies the search conditions related
to the item. An input item in which hyphen is set for convenience
denotes that no information corresponding to the item exists in the
reception packet corresponding to the table entry and, (even if
corresponding information exists), the search condition regarding
the item is not satisfied.
[0093] As will be described hereinlater, the routing information
table 150 is searched at two stages on the basis of internal header
information added to a reception packet by each of line interfaces.
In the search at the first stage, the table is searched by using
all of the items (input port number IN11, input L2 identifier IN12
and destination IP address IN13) of the input information IN1 as
search keys (search conditions). When there is a hit entry, the
reception packet is processed according to the output information
OUT1 of the entry. When there is no hit entry in the search at the
first stage, by using the destination IP address IN13 as a specific
item as a search key, the table search at the second stage is
executed. The reception packet is processed according to the output
information OUT1 of the hit entry.
[0094] For example, when attention is focused on the route RT11, an
IP packet transmitted from the host IP11 to the host IP13 is
supplied via the router R11 to the input port having the port
number #11'' in the edge node E11. In this case, in the table entry
EN101 in which the input port number IN11 is "#11", a hyphen is set
as the value of the input L2 identifier IN12. Consequently, the
search at the first stage fails and table search at the second
stage by using the destination IP address "IP13" as a search key is
executed. Since the entry EN101 is retrieved by the table search at
the second stage, the reception packet is subjected to a protocol
process for "MPLS edge-ingress forwarding" indicated by the
forwarding type OUT11 and is forwarded as an MPLS packet added with
a label "LabelL11" indicated by the output L2 identifier OUT13 to
the output port of the port number "#13" indicated by the output
port number OUT12
[0095] When attention is focused on the route RT12, an IP packet
transmitted from the host IP13 to the host IP11 is forwarded to the
edge node E12 via the router R13. The IP packet is converted to an
MPLS packet in the edge node 12 by a manner similar to that of the
edge node E11. The MPLS packet is supplied via the core node C11
from the input port having the port number "#13" to the edge node
E11. At this time, the label of the input MPLS packet is converted
to "L12" by the label switching in the core node C11. The edge node
E11 executes the table search at the first stage by using the input
port number "#13", the input L2 identifier "L12" and the
destination IP address "IP11" of the reception packet as search
keys. In this case, in the entry EN1012 in which the input port
number IN11 is "#13", a hyphen is set as the value of the input L2
identifier IN12, the table search fails and the table search at the
second stage by using the destination IP address "IP11" as input
information is executed. By the table search at the second stage,
the entry EN102 is retrieved and the reception MPLS packet is
transmitted to the output port of the number #11'' indicated by the
output port number OUT11 in the entry EN102 by the MPLS edge-egress
forwarding shown by the forwarding type OUT11. In this case, the
reception MPLS packet is converted to an IP packet having output L2
information "L2inf li" in accordance with the output L2 identifier
OUT13.
[0096] When attention is paid to the route RT13, an IP packet
transmitted from the host IP11 to the host IP12 is inputted via the
router R11 to the input port of the port number #11'' of the edge
node E11. In this case, in a manner similar to the reception packet
of the route RT11, the table search at the first stage fails and
the entry EN103 is retrieved by the table search at the second
stage by using the destination IP address IP12 as input
information. The reception packet is, therefore, transmitted to the
output port of the number #12'' indicated by the output port number
OUT12 in the entry EN103 by the IP forwarding shown by the
forwarding type OUT11. At this time, the reception packet is
converted to the IP packet which includes the output L2 information
"L2inf 1j" indicated by the output L2 identifier OUT13 in the layer
2 header.
[0097] When attention is focused on the route RT14, an IP packet
transmitted from the host IP14 to the host IP13 is inputted via the
router R14 to the edge node E13 and is converted to the MPLS packet
by the edge node E13. After that, the MPLS packet is inputted to
the input port of the port number "#14" in the edge node E11 via
the core node C12. The label of the MPLS packet is changed to "L14"
by the label conversion of the core node C12. In this case, the
entry EN104 is retrieved by the table search at the first stage,
the received MTLS packet is forwarded to the output port of the
port number "#12" indicated by the output port number OUT12 in the
entry EN104 by the MPLS core forwarding (POS-POS) indicated by the
forwarding type OUT11. At this time, the label of the reception
MPLS packet is converted to "LabelL13" indicated by the output L2
identifier OUT13.
[0098] As obviously understood from the above description, in the
present invention, by defining the output information including the
forwarding type OUT11 in each of the entries in the routing
information table 150 which is referred to on the basis of the
routing information (input port identifier and header information)
of a reception packet, a plurality of kinds of packet forwarding of
different protocol processes can be performed by a single MPLS
node. In the embodiment shown in FIGS. 1 and 2, the label
information of the layer 2.5 to be added to the forwarding packet
in the MPLS network and routing information (layer 2 information)
of the layer 2 to be added to the forwarding packet in the IP
network are defined in a lump as a "layer identifier". By setting
the output L2 identifier indicative of the label information or the
layer 2 information to be added to the output packet as output
information of each of the entries in the routing information table
150, both the IP forwarding function and the MPLS forwarding
function can be realized by a single MPLS node.
[0099] FIG. 3 shows an embodiment of a label switching type packet
forwarding apparatus (hereinbelow, called an MPLS node) 10
according to the invention typified by the above-described edge
node E11.
[0100] The MPLS node 10 comprises a control unit 11, a switching
unit 12, and a plurality of input line interface boards 13 (13-1 to
13-n) and output line interface boards 14 (14-1 to 14-n) which are
connected to the switching unit 12.
[0101] Each of the input line interface boards 13 comprises an
ingress routing unit 20 connected to the switching unit 12, and a
plurality of input line interface units 30 (30-1 to 30-m) connected
to the ingress routing unit 20. A plurality of input lines each
having peculiar input port number are connected to each of the
input line interface units 30. The routing information table 150
shown in FIG. 2 is a part of the ingress routing unit 20. The table
entries are updated by the control unit 11.
[0102] On the other hand, each of the output line interface boards
14 comprises an egress routing unit 40 connected to the switching
unit 12 and a plurality of output line interface units 50 (50-1 to
50-m) connected to the egress routing unit 40. A plurality of
output lines each having a peculiar output port number are
connected to each of the output line interface units 50. An output
line interface unit 50-j of an output line interface board 14-i
corresponds to an input line interface unit 30-j of an input line
interface board 13-i. That is, the MPLS node 10 has a plurality of
pairs of input and output lines.
[0103] Each of the input line interface units 30 performs protocol
processes of the layer 1 and layer 2 on a packet (or ATM cells)
received from an input line and forwards the reception packet to
the ingress routing unit 20. At this time, an internal header H6 is
added to the reception packet as shown in FIG. 4. FIG. 4 shows, as
an example of a reception packet, an MPLS packet obtained by adding
the Shim header H4 and the L2 header H5 to an IP packet comprising
of the IP payload D and the IP header H1. The format of the
reception packet differs according to a communication protocol
applied to each of the input lines. For example, a reception packet
from the input line connected to the IP network does not include
the Shim header H4.
[0104] The internal header H6 has, for example as shown in FIG. 5,
an identifier H61 of an egress routing unit, input port number H62,
an input L2 identifier H63, a destination IP address H64, a
forwarding type H65, output port number H66, and an output L2
identifier H67. In the embodiment, the output line interface board
14 (14-1 to 14-n) is specified by the identifier H61 of the egress
routing unit, and an output line in each of the output line
interface boards is specified by the output port number H66. For
example, the input port number H62 and the input L2 identifier H63
in the construction information of the internal header H6 are added
by each of the input line interface units 30 and the other
information is added by the ingress routing unit 20.
[0105] The switching unit 12 forwards a packet supplied from each
of the input line interface boards 13 to the output line interface
board 14 indicated by the identifier H61 of the egress routing unit
in the internal header. In each of the output line interface boards
14, by the egress routing unit 40, packets received from the
switching unit 12 are routed to the output line interface units 50
indicated by the output port numbers H66 each in the internal
header. Each of the output line interface units 50 removes the
internal header H6 from the reception packet, executes a header
converting process of the layer 2 in accordance with the forwarding
type H65 and the output L2 identifier H67, and then transmits the
packet (or ATM cell) to the output line indicated by the output
port number H66.
[0106] FIG. 6 shows the detailed construction of the input routing
unit 20 and the input line interface unit 30 in the input line
interface board 13.
[0107] The input line interface unit 30 comprises layer-1
processing units 31 (31-1 to 31-j) provided in correspondence with
input lines and a layer-2 processing unit 32 connected to the
layer-1 processing units 31. It is also possible to prepare the
layer-2 processing unit 32 for each layer-1 processing unit 31,
multiplex outputs of the plurality of layer-2 processing units 32
by a multiplexer and supply the resultant to the ingress routing
unit 20. The layer-1 processing unit 31 performs a signal receiving
process at the physical layer level of the communication line such
as light-electricity conversion to input packets in the layer 2 to
the layer-2 processing unit 32.
[0108] As shown in FIG. 7, the layer-2 processing unit 32 performs
termination processing for the layer 2 on a reception packet from
each of the layer-1 processing units 31 (step S01), sets the input
port number H62 and the input L2 identifier H63 to the internal
header H6 (S02) and forwards the reception packet to which the
internal header is added to the ingress routing unit 20 (S03). The
value of the input port number H62 to be set in the internal header
is specified from the peculiar number of the layer-1 processing
unit 31 which has received and processed the packet. The input L2
identifier H63 is specified by the contents of the L2 header H5
extracted from the reception packet.
[0109] The ingress routing unit 20 comprises, as shown in FIG. 6, a
multi-layer processing unit 21 connected to the layer-2 processing
unit 32 in each of the input line interface units 30 (30-1 to
30-m), a switching unit interface 22, a routing information
retrieval unit 23, and a routing information memory 24 in which,
for example, the routing information table 150 shown in FIG. 2 is
stored. The multi-layer processing unit 21 and the routing
information retrieval unit 23 may be formed on a single LSI.
[0110] As shown in FIG. 8, the multi-layer processing unit 21
performs termination processing for layer-3 on a packet received
from each of the input line interface units 30 (step S11), sets the
destination IP address H13 extracted from the IP header as a
destination IP address H64 in the internal header (S12), forwards
the input port number H62, input L2 identifier H63, and destination
IP address H64 as search keys of the routing information table to
the routing information retrieval unit 13 (S13) and waits for a
response from the routing information retrieval unit (S14).
[0111] When search key information is received from the multi-layer
processing unit 21, the routing information retrieval unit 13
searches the routing information table 150 by using all of given
search key items (input port number H62, input L2 identifier H63
and destination IP address H64) as search conditions in accordance
with the flowchart shown in FIG. 9 (step S101). The routing
information retrieval unit 13 checks the search result (S102). When
there is a table entry matching the search conditions, the routing
information retrieval unit 13 replies the output information OUT1
(forwarding type, output port number and output L2 identifier) of
the table entry to the multi-layer processing unit 21 (S103). In
the embodiment, in the table entry hit by the search conditions of
the first stage, the forwarding type OUT11 indicates the MPLS core
forwarding (POS-POS).
[0112] When the search at the first stage fails, the destination IP
address H64 is used as a search key and the routing table 150 is
again searched (S104). When the search result is checked (S105) and
there is a table entry which matches the search conditions, the
output information OUT1 of the table entry (forwarding type, output
port number and output L2 identifier) is returned to the
multi-layer processing unit 21 (S103). In the embodiment, in the
table entry hit by the search of the second stage, the forwarding
type OUT11 indicates one of the MPLS edge-ingress forwarding, MPLS
edge-egress forwarding, and IP forwarding. When the search of the
second stage also fails, default values indicative of unknown
routing information are replied to the multi-layer processing unit
21 (S106).
[0113] In the flowchart, the retrieval of the first stage is
performed by using all of items defined as the input information
IN1 in the routing information table as search conditions. In the
embodiment, however, since the entry for MPLS core forwarding to be
searched at the first stage has the destination IP address IN13 of
"Don't Care Value", the search at the first stage may use two items
of the input port number and the input L2 identifier as search
conditions.
[0114] When the output information OUT1 is received from the
routing information retrieval unit 23, as shown in FIG. 8, the
multi-layer processing unit 21 sets the identifier H61 of the
egress routing unit, forwarding type H65, output port number H66
and output L2 identifier H67 into the internal header (S15) and
forwards the reception packet to the switching unit 12 via the
switching unit interface 22 (S16). In this case, the identifier H61
of the egress routing unit corresponds to a few higher bits of the
output port number OUT12 shown in the table entry and the output
port number H66 corresponds to the rest of the bits of the output
port number OUT12. The switching unit 12 forwards the packet
received from each of the input interface boards 13 to the output
interface board 14 indicated by the identifier H61 of the egress
routing unit in the internal header.
[0115] FIG. 10 shows detailed constructions of the egress routing
unit 40 and the output line interface unit 50 in the output line
interface board 14.
[0116] The output line interface unit 50 comprises layer-processing
units 51 (51-1 to 51-j) provided in correspondence with output
lines and a layer-2 processing unit 52 connected to the layer-1
processing units 51. The egress routing unit 40 has a switching
unit interface 41 and a multi-layer processing unit 42 connected to
the layer-2 processing unit 52 in each of the output line interface
units 50 (50-1 to 50-m). Although the single layer-2 processing
unit 52 is shared by the plurality of layer-1 processing units 51
in this case, it is also possible to provide a layer-2 processing
unit 52 for each of the layer-1 processing units 51 and connect the
plurality of layer-2 processing units 52 to the multi-layer
processing unit 42 via a demultiplexer.
[0117] When a packet with the internal header is received via the
switching unit interface 41, as shown in FIG. 11, the multi-layer
processing unit 42 advances to one of the routines of the MPLS
edge-ingress forwarding (S22), MPLS edge-egress forwarding (S23),
MPLS core forwarding (S24) and IP forwarding (S25) in accordance
with the forwarding type H65 included in the internal header (S21).
The multi-layer processing unit 42 executes a TTL (Time To Live; it
is similarly done by hop number) process (526, S27, S28 or S29) and
a header converting process (S30, S31, S32 or S33) in accordance
with the forwarding type. In the embodiment, the multi-layer
processing unit 42 performs the header converting process on the
MPLS header and the IP header. As described above, when it is
regarded that the MPLS is in the layer 2.5, the multi-layer
processing unit 42 executes a protocol process regarding a layer
higher than the layer-2 processing unit 52.
[0118] For example, in the case of the MPLS edge-ingress
forwarding, after subtracting by 1 from the value of TTL H11
included in the IP header H1 by the TTL process (S26), the Shim
header H4 (refer to FIG. 26) including the resultant value as TTL
H42 is generated. In the header converting process (S30), the value
indicated by the output L2 identifier H67 of the internal header H6
is set in the label H41 in the Shim header H4 and the Shim header
H4 is inserted before the IP header in the reception packet (IP
packet).
[0119] In the case of the MPLS edge-egress forwarding, after
subtracting by 1 from the value of TTL H42 included in the Shim
header H4 of the reception packet by the TTL process (S27), the
resultant value is set in the TTL H11 in the IP header H1. In the
header converting process (S31), the Shim header H4 is eliminated
from the reception packet (MPLS packet).
[0120] In the case of the MPLS core forwarding (POS-POS forwarding
in the embodiment), after subtracting by 1 from the value of the
TTL H42 included in the Shim header H4 of a reception packet, the
value of the label H41 included in the Shim header H4 of the
reception packet is converted to a value indicated by the output L2
identifier H67 in the internal header H6.
[0121] In the case of the IP forwarding, after subtracting by 1
from the value of the TTL H11 included in the IP header H1 by the
TTL process (S29), a part of the IP header information such as the
value of Header Checksum H52 is updated by the header converting
process S33.
[0122] After the TTL process and the header converting process
according to the packet forwarding type, the multi-layer processing
unit 42 executes a QoS (Quality of Service) process (S34) and
forwards the reception packet to the output line interface board 50
corresponding to the output port number H66 (S35).
[0123] When a packet is received from the egress routing unit 40,
as shown in FIG. 12, the layer-2 processing unit 52 in each of the
output line interface boards 50 eliminates the internal header H6
from the reception packet (step S31). After executing a layer-2
protocol process (S32) on a packet to be transmitted, the layer-2
processing unit 52 forwards the transmission packet to the layer-1
processing unit 31 corresponding to the output port number H66 in
the internal header 6. In each of the layer-1 processing units 31,
the transmission packet received from the layer-2 processing unit
52 is converted into a predetermined signal in a physical layer and
the resultant signal is transmitted to the corresponding output
line.
[0124] For example, in the case where the output line is an ATM
line, in the layer-2 protocol process (S32), the transmission
packet is divided into a plurality of data blocks (payloads) each
having 48-byte length and a cell header including the VPI/VCI
indicated by the output L2 identifier H67 in the internal header is
added to each of the data blocks, thereby converting the
transmission packet into a plurality of ATM cells. In the case
where the output line is an IP network of Ethernet, an Ethernet
header H2 including the MAC address indicated by the output L2
identifier H67 in the internal header is generated by the layer-2
protocol process (S32), and is added to a transmission packet.
[0125] Although the protocol process (TTL process and header
converting process) according to the packet forwarding type is
executed by the egress routing unit 40 in the foregoing embodiment,
the protocol process may be performed by the ingress routing unit
20. In this case, for example, a protocol processing unit for
executing the TTL process and the header converting process is
disposed between the multi-layer processing unit 21 and the
switching unit interface 22 shown in FIG. 6 and a packet which has
been subjected to the converting process of the MPLS header and the
IP header is sent to the switching unit 11. The functions of the
multi-layer processing units 21 and 42 and the functions of the
routing information retrieval unit 23 and the protocol processing
unit shown in the flowcharts can be realized by a high-speed system
LSI chip by the semiconductor technique such as gate array or
ASIC.
[0126] FIG. 13 shows a network partially including a virtual
private network VPN formed by MPLS nodes, according to a second
embodiment of the invention.
[0127] In the embodiment, the MPLS domain D2 comprises edge nodes
E21, E22 and E23 and core nodes C21 and C22. The core nodes C21 and
C22 and the routers R21, R22, R23 and R24 on the IP network side
are connected to the edge node E21 on which attention is focused.
Among the routers, the routers R21 and R22 are connected to the
input/output port of the port number #21 in the edge node E21 via a
multiplexing apparatus (L2MUX) X21 such as an ATM multiplexing
apparatus. The routers R23 and R24 are connected to the input and
output ports of the port numbers #22 and #23 of the edge node E21,
respectively. Routers R25 and R26 of the IP network are connected
to the other edge nodes E22 and E23, respectively.
[0128] In FIG. 13, a host IP21 connected to the router R21 and a
host IP22 connected to the router R25 construct a virtual private
network VPN-A. A host IP21 connected to the router R22 and a host
IP22 connected to the router R26 construct another virtual private
network VPN-B. In the virtual private network, private IP addresses
can be used in each network (VAN). Consequently, if VANs are
different from each other, IP addresses used may be overlapped.
[0129] It is defined here that a route of an IP packet transmitted
from the host IP21 in the VPN-A to the host IP22 in the VPN-A is
RT21 and a route of an IP packet transmitted from the host IP21 in
the VPN-A to the host IP23 connected to the router R23 is RT22. It
is also defined that a route of an IP packet transmitted from the
host IP21 in the VPN-B to the host IP22 in the VPN-B is RT23 and a
route of an IP packet transmitted from the host IP21 in the VPN-B
to the host IP24 connected to the router R24 is RT24. It is assumed
that L2 MUX X21 and the edge node E21 are connected via an ATM
line, the packet of RT21 is ATM multiplexed by a VPI/VCI value
"VCIv21", the packet of RT22 is ATM multiplexed by a VPI/VCI value
"VCIv22" and packets of RT23 and RT24 are ATM multiplexed by
VPI/VCI values "VCIv23"
[0130] In the embodiment, the edge node E21 has a routing
information table 160 shown in FIG. 14. Each of the entries in the
table 160 has items similar to those in the table 150 shown in the
first embodiment and includes entries EN201 to EN204 corresponding
to RT21 to RT24.
[0131] The network of FIG. 13 includes not only the routes shown in
the diagram but also, for example, MPLS edge-egress forwarding
routes for forwarding packets from the MPLS domain D2 to the
external ATM lines in the direction opposite to the routes RT21 and
RT23, an MPLS edge-ingress forwarding route for forwarding a packet
from the host IP24 to the host IP22 in the VPN-B, an MPLS
edge-egress forwarding route opposite to the MPLS edge-ingress
forwarding route, and an MPLS core forwarding route for switching
packets in the MPLS domain D2. The routing information table 160
therefore includes table entries of forwarding types other than the
entries EN201 to EN204. These entries are substantially the same as
those in the first embodiment which have been described except for
the contents of the input/output L2 identifier. Consequently, the
description is omitted here.
[0132] When attention is paid to the route RT21 in the network of
FIG. 13, a packet transmitted from the host IP21 in the VAN-A to
the host IP22 is converted to ATM cells each having VPI/VCI value
"VCIv22" by the L2 MUX X21, and these ATM cells is supplied to the
input port of the port number #21 in the edge node E21.
Consequently, when the table search at the first stage (step S101
in FIG. 9) is executed by using the port number "#21", the input L2
identifier "VCIv22", and the destination IP address "IP22" as
search conditions in the routing information retrieval unit 23, the
table entry EN201 is retrieved.
[0133] When attention is paid on the route RT22, a packet
transmitted from the host IP21 in the VAN-A to the router host IP23
is converted to ATM cells by the L2 MUX X21 in a manner similar to
the route RT21, and these ATM cells are supplied from the input
port of the port number #21 to the edge node E21. In this case,
since the VPI/VCI value of each ATM cell is "VCIv23", the table
entry EN202 is retrieved by the table search at the first stage by
the routing information retrieval unit 23.
[0134] Packets of the routes RT23 and RT24 are converted to ATM
cells having the same VPI/VCI value "VCIv23" by the L2MUX X21.
These ATM cells are supplied to the edge node E21 from the input
port of the port number "#21". Since the destination IPS addresses
of the packets are "IP22" in the route RT23 and "IP24" in the route
RT24, the table entry EN203 is retrieved for the reception packet
of the route RT23 and the table entry EN204 is retrieved for the
reception packet of the route RT24 by the table search at the first
stage by the routing information retrieval unit 23.
[0135] Even in the case where the edge nodes in the MPLS domain are
connected to the VPNs and the same destination IP address indicates
different destination apparatuses according to the VPNs, in a
manner similar to the first embodiment, by searching the routing
information table by using the combination of the input port
number, input L2 identifier, and destination IP address as
searching conditions, packet forwarding to the output route
corresponding to the reception packet and the protocol process
according to the packet forwarding type can be executed.
[0136] In the embodiment, the case (case 1) where the value of the
L2 identifier (VPI/VCI) in the route RT21 and that in the route
RT22 are different from each other and the case (case 2) where the
value of the L2 identifier in the route RT23 and that in the route
RT24 are the same even when packets are transmitted from the same
host to different destinations have been described. For example,
when the destination IP address is a peculiar address which is not
used in the other apparatus like the host IP23 in the route RT22,
"Don't Care Value" may be set for each of the input port IN11 and
the input L2 identifier IN12 of the corresponding table entry. When
the VPN can be identified only by the input port number in the edge
node E21, "Don't Care Value" or a hyphen (it denotes that the
search condition is not satisfied) may be set in the input L2
identifier IN12. The item can be substantially eliminated from the
search conditions.
[0137] In the embodiment shown in FIG. 14, to make the explanation
simpler, the output L2 identifier OUT13 is designated by one label
value. It is also possible to designate a plurality of labels as
the output L2 identifiers and, for example, like a label stack
described in the draft of the IETF, it is also possible to insert
two Shim headers H4 of the MPLS. In the VPN using the MPLS, for
example, there is a case such that VPN identification information
is necessary as a first label and routing information to a
neighboring MPLS node is necessary as a second label. In such a
case as well, it is sufficient to set the two label values as the
output L2 identifier OUT13 of the routing information table
160.
[0138] FIG. 15 shows an example of a network construction as a
third embodiment of the invention, in which the use of an edge node
in the MPLS domain is preliminarily limited, thereby enabling the
search of the routing information table be simplified.
[0139] In the case of executing the MPLS core forwarding described
in the first embodiment and the MPLS edge forwarding of the VPN
described in the second embodiment, the input port number and the
input L2 identifier are necessary as search conditions of the
routing information table. When the use of the edge node in the
MPLS domain is limited and it is unnecessary to perform the MPLS
core forwarding and the MPLS edge forwarding of the VPN, only the
destination IP address is necessary as the search condition of the
routing information table.
[0140] For example, if there is no core node C12 in the network
shown in FIG. 1, the network construction is as shown in FIG. 15
and the edge node E11 is related to the route RT11 of an IP packet
transmitted from the host IP11 to the host IP13, the route RT12 of
an IP packet which is in the direction opposite to the route RT11,
and the route RT13 of an IP packet transmitted from the host IP11
to the host IP12. In this case, only the IP forwarding function and
the MPLS edge forwarding function are necessary for the edge node
E11. In the network construction shown in the diagram, besides the
above routes, the route for forwarding a packet between the hosts
IP12 and IP13 and the route of a packet transmitted from the host
IP12 to the host IP11 exist. Since the packet forwarding over the
routes is similar to that over the routes RT11 to RT13, the
description is omitted here.
[0141] In the case of the above network construction, a routing
information table 170 of the edge node E11 is obtained by, as shown
in FIG. 16, omitting the entry EN104 for the route RT14 from the
table 150 shown in FIG. 2. All of table entries of the routing
information table 170 have the contents which are hit in the
searching step S104 of the second stage in the routing information
retrieving flowchart shown in FIG. 9. Consequently, when it is
preliminarily known that the network construction does not need the
search (S101) of the first stage like the embodiment, the following
manner can be used. In order to increase the processing speed of
the edge node, steps S101 and S102 are omitted from the routing
information retrieving flowchart shown in FIG. 9 and the routing
information retrieval unit 23 searches the routing information
table by using only the destination IP address as a search
condition from the beginning.
[0142] In this case, the input port IN11 and the input L2
identifier IN12 are unnecessary in the routing information table
170. Whether those items are left in the table or eliminated is
determined depending on prediction of a change in an environment to
which the core node is applied. In order to make the change in the
network construction remain flexible, the table construction is
left as it is and only the routing information retrieving function
is made adapted to the present network construction. When the
retrieval of two stages becomes necessary, only the function of the
routing information retrieval unit 23 is changed to the state of
FIG. 9.
[0143] FIG. 17 shows an example of the network construction in
which POS lines and ATM lines are included in an MPLS domain D4 as
a fourth embodiment of the invention.
[0144] The MPLS domain D4 comprises edge nodes E41 to E44 and a
core node C41 for mutually connecting the edge nodes. Hosts IP41 to
IP44 are connected to the edge nodes E41 to E44 via routers R41 to
R44, respectively. In the embodiment, attention is paid only to the
MPLS core forwarding performed by the core node C41 and is not paid
to the IP forwarding and the MPLS edge forwarding described in the
first embodiment and the packet forwarding for the VPN described in
the second embodiment. The core node C41 performs communications
with the edge nodes E41 and E42 over the POS lines and performs
communications with the edge nodes E43 and E44 via ATM lines. The
core node C41 has, for example, a routing information table 180
shown in FIG. 18. In the MPLS communication using ATM lines, in a
manner similar to the MPLS communications in POS or Ethernet, there
are two cases; a case of using a Shim header and a case of using
the VPI/VCI of the ATM header as a label in place of the Shim
header. The latter case will be described here.
[0145] In the network of FIG. 17, it is assumed that a route of an
IP packet transmitted from the host IP41 to the host IP43 is RT41,
a route of an IP packet transmitted from the host IP44 to the host
IP42 is RT42, a route of an IP packet transmitted from the host
IP41 to the host IP42 is RT43, and a route of an IP packet
transmitted from the host IP43 to the host IP44 is RT44.
[0146] In this case, the routing information table 180 of the core
node C41 includes, as shown in FIG. 18, table entries EN401 to
EN404 corresponding to the routes RT41 to RT44, respectively.
"Label L41" and "Label L42" indicated as the input L2 identifiers
IN12 denote values of labels H41 to be added to the Shim headers of
the MPLS of packets on the routes RT41 and RT43 received from the
POS lines connected to the input port of the port number #41.
"VCIv47" and "VCIv46" indicate values of the VPI/VCI to be added as
labels to packets on the routes RT42 and RT44 received through ATM
lines connected to the input ports of the port numbers #44 and #43,
respectively.
[0147] When the core node C41 receives the MPLS packets of the
routes RT41 to RT44, the routing information retrieval unit 23 in
the input routing unit 20 corresponding to each input line searches
the routing information table 180 by the procedure shown in FIG. 9.
In the embodiment, the table entries EN401 to EN404 are retrieved
in the table searching step S101 at the first stage in
correspondence with the reception packets of the routes RT41 to
RT44. By the multi-layer processing unit 42 in the output routing
unit 40, the protocol process corresponding to the forwarding type
OUT11 of each of the entries is executed.
[0148] FIG. 19 shows the flowchart of the protocol process executed
by the multi-layer processing unit 42 in the embodiment.
[0149] When a packet with the internal header is received via the
switching interface 41, in accordance with the forwarding type H65
included in the internal header, the multi-layer processing unit 42
advances one of the processing routines (S21); the MPLS core
(POS-ATM) forwarding for forwarding a reception packet from the POS
line to the ATM line (S241), MPLS core (ATM-POS) forwarding for
forwarding a reception packet from the ATM line to the POS line
(S242), MPLS core (POS-POS) forwarding for forwarding a reception
packet from the POS line to the POS line (S243), and MPLS core
(ATM-ATM) forwarding for forwarding a packet from the ATM line to
the ATM line (S244).
[0150] As obviously understood from the ATM header format shown in
FIG. 24, the ATM header does not include TTL information. In each
of the MPLS core forwarding of POS-ATM, ATM-POS, and POS-POS (S241
to S243), a TTL (Time To Live: similar with the hop count) process
(S281, S282 or S283) and a header converting process (S321, S322 or
S323) are performed in accordance with the forwarding type. In the
MPLS core (ATM-ATM) forwarding (S244), the TTL process and the
header converting process in the layer are omitted.
[0151] For example, in the TTL process (S281) of the MPLS core
(POS-ATM) forwarding (S241) performed by a node positioned at the
entrance of the ATM line section, the number k of MPLS nodes (MPLS
hop count) through which the reception packet passes in the ATM
line section is subtracted from the value of TTL H42 extracted from
the Shim header of the reception packet and the resultant value is
set as the TTL H11 of the IP packet. In the header converting
process (S321), the Shim header H4 is removed from the reception
packet (MPLS packet) and the VPI/VCI value indicated by the output
L2 identifier H67 in the internal header H6 is added as a new label
to the reception packet.
[0152] By preliminarily subtracting the number of hops in the ATM
line section in a lump by the TTL process (S281), even when each of
the MPLS nodes positioning in the ATM line section performs the
MPLS core (ATM-ATM) forwarding which does not include the TTL
process (S244), the accurate TTL can be transmitted to the node
positioning at the exit of the ATM line section.
[0153] In the TTL process (S282) of the MPLS core (ATM-POS)
forwarding (S242) performed by the node positioning at the exit of
the ATM line section, after subtracting by 1 from the value of the
TTL H11 included in the IP header H1 of the reception packet, the
resultant is set as the TTL H42 in the Shim header H4. In the
header converting process (S322), the Shim header H4 is added to
the reception packet (MPLS packet). As the label H41 of the Shim
header H4, the value indicated by the output L2 identifier H67 in
the internal header H6 is set.
[0154] In the TTL process (S282) of the MPLS core (POS-POS)
forwarding (S243) for forwarding a reception packet from a POS line
to a POS line, 1 is subtracted from the value of the TTL H42
included in the Shim header H4 of the reception packet. In the
header converting process (S323), the value of the label H41
included in the Shim header H4 of the reception packet is changed
to the value indicated by the output L2 identifier H67 in the
internal header H6.
[0155] When the processing routines S241 to S244 shown in FIG. 19
are applied in place of the MPLS core forwarding process routine
S24 in the multi-layer processing unit shown in FIG. 11, the edge
node E11 in the first embodiment can be provided with the core
forwarding function between ATM lines and between the ATM line and
the POS line as described in the fourth embodiment. Since the table
entries EN401 to EN404 for MPLS core forwarding shown in the
routing information table 180 can be specified by a combination of
the input port number IN11 and the input L2 identifier IN12 in a
manner similar to the first embodiment, "Don't Care Value" can be
set in the destination IP address IN13 in each of the entries.
[0156] As obviously understood from the embodiments, the packet
forwarding apparatus of the invention can be connected with a
number of kinds of communication lines of different communication
protocols and can easily realize a number of kinds of protocol
conversions according to combinations of input/output lines.
Basically, apparatuses of the same structure can satisfy various
network demands. The packet forwarding apparatus of the invention
can therefore reduce the cost by mass production. When the
apparatus of the invention is applied, the construction of a
network can be flexibly expanded or changed. It therefore
facilitates a shift to a network construction of a different
communication protocol and the maintenance and control of a
node.
[0157] According to the present invention, since the label
switching type packet forwarding apparatus has a routing
information table in which the packet forwarding type is designated
in correspondence with the routing information peculiar to the
reception packet which is known at the time of receiving a packet,
it is able to forward packets between lines of different protocols
by performing the header converting process of a reception packet
in accordance with the packet forwarding type designated in the
routing information table.
* * * * *