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Table Of Contents
MPLS Traffic Engineering Forwarding Adjacency
Related Features and Technologies
Configuring a Tunnel Interface for MPLS TE Forwarding Adjacency
Configuring MPLS TE Forwarding Adjacency
Configuring IS-IS for MPLS TE Forwarding Adjacency
Verifying MPLS TE Forwarding Adjacency
Monitoring and Maintaining MPLS TE Forwarding Adjacency
MPLS TE Forwarding Adjacency Example
debug mpls traffic-eng forwarding-adjacency
show mpls traffic-eng forwarding-adjacency
tunnel mpls traffic-eng forwarding-adjacency
MPLS Traffic Engineering Forwarding Adjacency
First Published: January 29, 2001Last Updated: March 16, 2006This document describes the Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) Forwarding Adjacency feature in Cisco IOS Release 12.2(18)S. It identifies the supported platforms, provides configuration examples, and lists related IOS command line interface (CLI) commands.
History for the MPLS Traffic Engineering Forwarding Adjacency
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.
Contents
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Monitoring and Maintaining MPLS TE Forwarding Adjacency
Feature Overview
The MPLS TE Forwarding Adjacency feature allows a network administrator to handle a traffic engineering, label-switched path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network based on the Shortest Path First (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.
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 head end of any TE tunnels.
Restrictions
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Related Features and Technologies
The MPLS TE Forwarding Adjacency feature is related to the Resource Reservation Protocol (RSVP) and MPLS traffic engineering features. (See the "Related Documents" section.)
Prerequisites
Your network must support the following Cisco IOS features before enabling the MPLS TE Forwarding Adjacency feature:
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Configuration Tasks
See the following sections for configuration tasks for the MPLS TE Forwarding Adjacency feature. Each task in the list is identified as either required or optional.
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Configuring a Tunnel Interface for MPLS TE Forwarding Adjacency
To configure a tunnel interface for an MPLS TE forwarding adjacency, use the following commands beginning in global configuration mode
SUMMARY STEPS
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DETAILED STEPS
Configuring MPLS TE Forwarding Adjacency
To configure an MPLS TE forwarding adjacency, use the following command in interface configuration mode:
Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency {holdtime value}
Advertises a TE tunnel as a link in an IGP network.
Note
Configuring IS-IS for MPLS TE Forwarding Adjacency
To configure an IS-IS metric for an MPLS TE forwarding adjacency, use the following command in interface configuration mode:
Verifying MPLS TE Forwarding Adjacency
To verify MPLS TE forwarding adjacency configuration, use this procedure:
Step 1
Router# show mpls traffic-eng forwarding-adjacencydestination 0168.0001.0007.00 has 1 tunnelsTunnel7 (traffic share 100000, nexthop 192.168.1.7)(flags:Announce Forward-Adjacency, holdtime 0)Router# show mpls traffic-eng forwarding-adjacency 192.168.1.7destination 0168.0001.0007.00 has 1 tunnelsTunnel7 (traffic share 100000, nexthop 192.168.1.7)(flags:Announce Forward-Adjacency, holdtime 0)
Monitoring and Maintaining MPLS TE Forwarding Adjacency
To monitor and maintain an MPLS TE forwarding adjacency, use the following commands in EXEC mode:
Configuration Examples
This section provides a configuration example for the MPLS TE Forwarding Adjacency feature using an IS-IS metric.
MPLS TE Forwarding Adjacency Example
The following output shows a tunnel interface, a forwarding adjacency, and an IS-IS metric being configured:
Router# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# interface tunnel 7Router(config-if)# tunnel mpls traffic-eng forwarding-adjacencyRouter(config-if)# isis metric 2 level 1Here is sample output in which a forwarding adjacency has been configured:
Router# show runBuilding configuration...Current configuration :364 bytes!interface Tunnel7ip unnumbered Loopback0no ip directed-broadcasttunnel destination 192.168.1.7tunnel mode mpls traffic-engtunnel mpls traffic-eng forwarding-adjacencytunnel mpls traffic-eng priority 7 7tunnel mpls traffic-eng path-option 10 explicit name shortisis metric 2 level 1
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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 has to 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 AB and AC links is shared.
Additional References
The following sections provide references related to MPLS Traffic Engineering Forwarding Adjacency.
Related Documents
Switching services configuration
Cisco IOS Switching Services Configuration Guide, Release 12.2
Switching services commands
Cisco IOS Switching Services Command Reference, Release 12.2
Intermediate System-to-Intermediate System (IS-IS) TLVs
Intermediate System-to-Intermediate System (IS-IS) TLVs (white paper)
Standards
MIBs
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
Technical Assistance
Command Reference
This section documents modified commands only.
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debug mpls traffic-eng forwarding-adjacency
To display debug messages for traffic engineering (TE) forwarding-adjacency events, use the debug mpls traffic-eng forwarding-adjacency command in privileged EXEC mode. To disable debugging output, use the no form of this command.
debug mpls traffic-eng forwarding-adjacency
no debug mpls traffic-eng forwarding-adjacency
Syntax Description
This command has no arguments or keywords.
Defaults
This command is disabled by default.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Use the debug mpls traffic-eng forwarding-adjacency command to troubleshoot any problems that occur after you configure the tunnel mpls traffic-eng forwarding-adjacency command.
Examples
The following is sample output from the debug mpls traffic-eng forwarding-adjacency command:
Router# debug mpls traffic-eng forwarding-adjacencyMPLS traffic-eng debugging is onWith a tunnel configured, the following output appears:
interface Tunnel0ip unnumbered Loopback0no ip directed-broadcasttunnel destination 192.168.1.7tunnel mode mpls traffic-engtunnel mpls traffic-eng forwarding-adjacencytunnel mpls traffic-eng priority 7 7tunnel mpls traffic-eng path-option 10 dynamicendWhen the tunnel comes up, it generates the following debug output:
*Oct 2 12:27:07.846:TE-Auto:announcement that destination 0168.0001.0007.00 has 1 tunnels*Oct 2 12:27:07.846: Tunnel0 (traffic share 142857, nexthop 192.168.1.7)*Oct 2 12:27:07.846: (flags: Forward-Adjacency, holdtime 0)Related Commands
show mpls traffic-eng forwarding-adjacency
To display traffic engineering (TE) tunnels that are advertised as links in an Interior Gateway Protocol (IGP) network, use the show mpls traffic-eng forwarding-adjacency command in EXEC mode.
show mpls traffic-eng forwarding-adjacency ip address
Syntax Description
Defaults
No default behavior or values.
Command Modes
EXEC
Command History
Usage Guidelines
Use the show mpls traffic-eng forwarding-adjacency command to display information about tunnels configured with the tunnel mpls traffic-eng forwarding-adjacency command.
Examples
The following is sample output from the show mpls traffic-eng forwarding-adjacency command:
Router# show mpls traffic-eng forwarding-adjacency ?A.B.C.D destination address for forwarding-adjacency tunnels| Output modifiers<cr>Here is sample output in which a forwarding adjacency is enabled:
Router# show runBuilding configuration...Current configuration :364 bytes!interface Tunnel7ip unnumbered Loopback0no ip directed-broadcasttunnel destination 192.168.1.7tunnel mode mpls traffic-engtunnel mpls traffic-eng forwarding-adjacencytunnel mpls traffic-eng priority 7 7tunnel mpls traffic-eng path-option 10 explicit name shortisis metric 2 level 1endUse the show mpls traffic-eng forwarding-adjacency command again to see the current tunnels:
Router# show mpls traffic-eng forwarding-adjacencydestination 0168.0001.0007.00 has 1 tunnelsTunnel7 (traffic share 100000, nexthop 192.168.1.7)(flags:Announce Forward-Adjacency, holdtime 0)Router# show mpls traffic-eng forwarding-adjacency 192.168.1.7destination 0168.0001.0007.00 has 1 tunnelsTunnel7 (traffic share 100000, nexthop 192.168.1.7)(flags:Announce Forward-Adjacency, holdtime 0)Related Commands
tunnel mpls traffic-eng forwarding-adjacency
To advertise a traffic engineering (TE) tunnel as a link in an Interior Gateway Protocol (IGP) network, use the tunnel mpls traffic-eng forwarding-adjacency command in interface configuration mode. To disable the functionality, use the no form of this command.
tunnel mpls traffic-eng forwarding-adjacency {holdtime value}
no tunnel mpls traffic-eng forwarding-adjacency
Syntax Description
holdtime value
Time in milliseconds (ms) that a TE tunnel waits after going down before informing the network. The range is 0 to 4,294,967,295 ms. The default value is 0.
Defaults
The default value is 0.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use the tunnel mpls traffic-eng forwarding-adjacency command with the isis metric command to avoid inefficient forwarding behavior. Ensure that any nodes traversed by the TE tunnel being advertised do not consider the TE tunnel as part of the shortest path to the destination.
Note
Examples
In the following example, the holdtime is set to 10,000 milliseconds:
Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency holdtime 10000In the following example, the holdtime defaults to 0:
Router(config-if)# tunnel mpls traffic-eng forwarding-adjacencyRelated Commands
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 (CDP) 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.
Note
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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