MPLS Traffic Engineering Forwarding Adjacency
First Published: January 29, 2001
Last Updated: May 4, 2009
The MPLS Traffic Engineering Forwarding Adjacency feature allows a network administrator to handle a traffic engineering (TE) label switched path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network based on the Shortest Path First (SPF) algorithm.
Both Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) are supported.
Finding Feature Information
For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for MPLS Traffic Engineering Forwarding Adjacency" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•Prerequisites for MPLS Traffic Engineering Forwarding Adjacency
•Restrictions for MPLS Traffic Engineering Forwarding Adjacency
•Information About MPLS Traffic Engineering Forwarding Adjacency
•How to Configure MPLS Traffic Engineering Forwarding Adjacency
•Configuration Examples for MPLS Traffic Engineering Forwarding Adjacency
•Additional References
•Feature Information for MPLS Traffic Engineering Forwarding Adjacency
•Glossary
Prerequisites for MPLS Traffic Engineering Forwarding Adjacency
Your network must support the following Cisco IOS XE features:
•Multiprotocol Label Switching (MPLS)
•IP Cisco Express Forwarding
•IS-IS
Restrictions for MPLS Traffic Engineering Forwarding Adjacency
•Using the MPLS Traffic Engineering Forwarding Adjacency feature increases the size of the IGP database by advertising a TE tunnel as a link.
•When the MPLS Traffic Engineering Forwarding Adjacency feature is enabled on a TE tunnel, the link is advertised in the IGP network as a type, length, value (TLV) 22 object without any TE sub-TLV.
•You must configure MPLS TE forwarding adjacency tunnels bidirectionally.
Information About MPLS Traffic Engineering Forwarding Adjacency
•MPLS Traffic Engineering Forwarding Adjacency Functionality
•MPLS Traffic Engineering Forwarding Adjacency Benefits
MPLS Traffic Engineering Forwarding Adjacency Functionality
The MPLS Traffic Engineering Forwarding Adjacency feature allows a network administrator to handle a TE LSP tunnel as a link in an IGP network based on the SPF algorithm. A forwarding adjacency can be created between routers regardless of their location in the network. The routers can be located multiple hops from each other, as shown in Figure 1.
Figure 1 Forwarding Adjacency Topology
As a result, a TE tunnel is advertised as a link in an IGP network with the link's cost associated with it.
Routers outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.
MPLS Traffic Engineering Forwarding Adjacency Benefits
TE tunnel interfaces advertised for SPF—TE tunnel interfaces are advertised in the IGP network just like any other links. Routers can then use these advertisements in their IGPs to compute the SPF even if they are not the headend of any TE tunnels.
How to Configure MPLS Traffic Engineering Forwarding Adjacency
•Configuring a Tunnel Interface for MPLS TE Forwarding Adjacency (required)
•Configuring MPLS TE Forwarding Adjacency on Tunnels (required)
•Verifying MPLS TE Forwarding Adjacency (optional)
Configuring a Tunnel Interface for MPLS TE Forwarding Adjacency
SUMMARY STEPS
1. enable
2. configure terminal
3. interface tunnel number
4. exit
5. exit
DETAILED STEPS
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Step 1 |
enable
Router> enable |
Enables privileged EXEC mode. •Enter your password if prompted. |
Step 2 |
configure terminal
Router# configure terminal |
Enters global configuration mode. |
Step 3 |
interface tunnel number
Router(config)# interface tunnel 0 |
Designates a tunnel interface for the forwarding adjacency, and enters interface configuration mode. |
Step 4 |
exit
Router(config-if)# exit |
Exits interface configuration mode and returns to global configuration mode. |
Step 5 |
exit
Router(config)# exit |
Exits global configuration mode and returns to privileged EXEC mode. |
Configuring MPLS TE Forwarding Adjacency on Tunnels
Note You must configure a forwarding adjacency on two LSP tunnels bidirectionally, from A to B and B to A. Otherwise, the forwarding adjacency is advertised, but not used in the IGP network.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface tunnel number
4. tunnel mpls traffic-eng forwarding-adjacency [holdtime value]
5. isis metric {metric-value | maximum} {level-1 | level-2}
6. exit
7. exit
DETAILED STEPS
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Step 1 |
enable
Router> enable |
Enables privileged EXEC mode. •Enter your password if prompted. |
Step 2 |
configure terminal
Router# configure terminal |
Enters global configuration mode. |
Step 3 |
interface tunnel number
Router(config)# interface tunnel 0 |
Designates a tunnel interface for the forwarding adjacency, and enters interface configuration mode. |
Step 4 |
tunnel mpls traffic-eng forwarding-adjacency [holdtime value]
Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency |
Advertises a TE tunnel as a link in an IGP network. |
Step 5 |
isis metric {metric-value | maximum} {level-1 | level-2}
Router(config-if)# isis metric 2 level-1
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Configures the IS-IS metric for a tunnel interface to be used as a forwarding adjacency. •You should specify the isis metric command with level-1 or level-2 to be consistent with the IGP level at which you are performing traffic engineering. Otherwise, the metric has the default value of 10. |
Step 6 |
exit
Router(config-if)# exit |
Exits interface configuration mode and returns to global configuration mode. |
Step 7 |
exit
Router(config)# exit |
Exits global configuration mode and returns to privileged EXEC mode. |
Verifying MPLS TE Forwarding Adjacency
SUMMARY STEPS
1. enable
2. show mpls traffic-eng forwarding-adjacency [id-address]
3. show isis [process-tag] database [level-1] [level-2] [l1] [l2] [detail] [lspid]
4. exit
DETAILED STEPS
Step 1 enable
Use this command to enable privileged EXEC mode. Enter your password if prompted. For example:
Step 2 show mpls traffic-eng forwarding-adjacency [ip-address]
Use this command to see the current tunnels. For example:
Router# show mpls traffic-eng forwarding-adjacency
destination 0168.0001.0007.00 has 1 tunnels
Tunnel7 (traffic share 100000, nexthop 192.168.1.7)
(flags:Announce Forward-Adjacency, holdtime 0)
Router# show mpls traffic-eng forwarding-adjacency 192.168.1.7
destination 0168.0001.0007.00 has 1 tunnels
Tunnel7 (traffic share 100000, nexthop 192.168.1.7)
(flags:Announce Forward-Adjacency, holdtime 0)
Step 3 show isis [process-tag] database [level-1] [level-2] [l1] [l2] [detail] [lspid]
Use this command to display information about the IS-IS link-state database. For example:
Router# show isis database
IS-IS Level-1 Link State Database
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0C00.0C35.00-00 0x0000000C 0x5696 792 0/0/0
0000.0C00.40AF.00-00 0x00000009 0x8452 1077 1/0/0
0000.0C00.62E6.00-00 0x0000000A 0x38E7 383 0/0/0
0000.0C00.62E6.03-00 0x00000006 0x82BC 384 0/0/0
0800.2B16.24EA.00-00 0x00001D9F 0x8864 1188 1/0/0
0800.2B16.24EA.01-00 0x00001E36 0x0935 1198 1/0/0
IS-IS Level-2 Link State Database
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0C00.0C35.03-00 0x00000005 0x04C8 792 0/0/0
0000.0C00.3E51.00-00 0x00000007 0xAF96 758 0/0/0
0000.0C00.40AF.00-00 0x0000000A 0x3AA9 1077 0/0/0
Step 4 exit
Use this command to exit to user EXEC. For example:
Configuration Examples for MPLS Traffic Engineering Forwarding Adjacency
This section provides a configuration example for the MPLS Traffic Engineering Forwarding Adjacency feature using an IS-IS metric.
•Example: MPLS TE Forwarding Adjacency
Example: MPLS TE Forwarding Adjacency
The following output shows the configuration of a tunnel interface, a forwarding adjacency, and an IS-IS metric:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# interface tunnel 7
Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency
Router(config-if)# isis metric 2 level-1
Following is sample command output when a forwarding adjacency has been configured:
Router# show running-config
Building configuration...
Current configuration :364 bytes
tunnel destination 192.168.1.7
tunnel mode mpls traffic-eng
tunnel mpls traffic-eng forwarding-adjacency
tunnel mpls traffic-eng priority 7 7
tunnel mpls traffic-eng path-option 10 explicit name short
Note Do not specify the tunnel mpls traffic-eng autoroute announce command in your configuration when you are using forwarding adjacency.
Following is an example where forwarding adjacency is configured with OFPF:
Router# configure terminal
Router# show running-config
Building configuration...
Current configuration : 310 bytes
interface tunnel 1
tunnel destination 172.16.255.5
tunnel mode mpls traffic-eng
tunnel mpls traffic-eng forwarding-adjacency tunnel mpls
traffic-eng priority 7 7
tunnel mpls traffic-eng bandwidth 1000
tunnel mpls traffic-eng path-option 10 dynamic
end
Router# show mpls traffic-eng forwarding-adjacency
destination 172.16.255.5, area ospf 172 area 0, has 1 tunnels
Tunnel1 (load balancing metric 2000000, nexthop 172.16.255.5)
(flags: Forward-Adjacency, holdtime 0)
Usage Tips
In Figure 2, if you have no forwarding adjacencies configured for the TE tunnels between Band F and C and F, all the traffic that A must forward to F goes through B because B is the shortest path from A to F. (The cost from A to F is 15 through B and 20 through C.)
Figure 2 Using Forwarding Adjacencies
If you have forwarding adjacencies configured on the TE tunnels between B and F and C and F and also on the TE tunnels between F and B and F and C, then when A computes the SPF algorithm, A sees two equal cost paths of 11 to F. As a result, traffic across the A-B and A-C links is shared.
Additional References
Related Documents
Standards
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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MIBs
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No new or modified MIBs are supported by this feature, and support for existing standards has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs |
RFCs
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No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
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Technical Assistance
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The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
http://www.cisco.com/cisco/web/support/index.html |
Feature Information for MPLS Traffic Engineering Forwarding Adjacency
Table 1 lists the features in this module and provides links to specific configuration information.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.
Glossary
Cisco Express Forwarding—A scalable, distributed, Layer 3 switching solution designed to meet the future performance requirements of the Internet and enterprise networks.
forwarding adjacency—A traffic engineering link (or LSP) into an IS-IS/OSPF network.
IGP—Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common IGPs include Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).
IS-IS—Intermediate System-to-Intermediate System. Open System Interconnection (OSI) link-state hierarchical routing protocol whereby Intermediate System (IS) routers exchange routing information based on a single metric to determine network topology.
label switched path (LSP)—A sequence of hops (R0...Rn) in which a packet travels from R0 to Rn through label switching mechanisms. A switched path can be chosen dynamically, based on normal routing mechanisms, or through configuration.
label switched path (LSP) tunnel—A configured connection between two routers, using label switching to carry the packets.
MPLS—Multiprotocol Label Switching. A switching method that forwards IP traffic using a label. This label instructs the routers and the switches in the network where to forward the packets based on preestablished IP routing information.
OSPF—Open Shortest Path First. A link-state, hierarchical IGP routing algorithm proposed as a successor to RIP in the Internet community. OSPF features include least-cost routing, multipath routing, and load balancing. OSPF was derived from an early version of the IS-IS protocol. See also IS-IS.
SPF—Shortest Path First. A routing algorithm used as the basis for OSPF operations. When an SPF router is powered up, it initializes its routing-protocol data structures and then waits for indications from lower-layer protocols that its interfaces are functional.
TLV—type, length, value. A block of information embedded in Cisco Discovery Protocol advertisements.
traffic engineering—The techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods had been applied.
traffic engineering tunnel—A label switched tunnel that is used for traffic engineering. Such a tunnel is set up through means other than normal Layer 3 routing; it is used to direct traffic over a path different from the one that Layer 3 routing would cause the tunnel to take.
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Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
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