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MPLS Traffic Engineering Forwarding Adjacency

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MPLS Traffic Engineering Forwarding Adjacency

Table Of Contents

MPLS Traffic Engineering Forwarding Adjacency

Contents

Feature Overview

Benefits

Restrictions

Related Features and Technologies

Prerequisites

Configuration Tasks

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

Configuration Examples

MPLS TE Forwarding Adjacency Example

Usage Tips

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

debug mpls traffic-eng forwarding-adjacency

show mpls traffic-eng forwarding-adjacency

tunnel mpls traffic-eng forwarding-adjacency

Glossary


MPLS Traffic Engineering Forwarding Adjacency


First Published: January 29, 2001
Last Updated: March 16, 2006

This 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

Release
Modification

12.0(15)S

This feature was introduced.

12.0(16)ST

This feature was integrated into Cisco IOS Release 12.0(16)ST.

12.2(18)S

This feature was integrated into Cisco IOS Release 12.2(18)S.

12.2(18)SXD

This feature was integrated into Cisco IOS Release 12.2(18)SX.

12.2(27)SBC

This feature was integrated into Cisco IOS Release 12.2(27)SBC.

12.2(28)SB

This feature was integrated into Cisco IOS Release 12.2(28)SB


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

Feature Overview

Prerequisites

Configuration Tasks

Monitoring and Maintaining MPLS TE Forwarding Adjacency

Configuration Examples

Command Reference

Glossary

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

Using the MPLS TE Forwarding Adjacency feature increases the size of the IGP database by advertising a TE tunnel as a link.

The MPLS TE Forwarding Adjacency feature is supported by Intermediate System-to-Intermediate System (IS-IS). Open Shortest Path First (OSPF) support will be available in a future release.

When the MPLS TE Forwarding Adjacency feature is enabled on a TE tunnel, the link is advertised in the IGP network as a Type-Length-Value (TLV) 22 without any TE sub-TLV.

MPLS TE forwarding adjacency tunnels must be configured bidirectionally.

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:

Multiprotocol Label Switching (MPLS)

IP Cisco Express Forwarding

Intermediate System-to-Intermediate System (IS-IS)

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.

Configuring a Tunnel Interface for MPLS TE Forwarding Adjacency (required)

Configuring MPLS TE Forwarding Adjacency (required)

Configuring IS-IS for MPLS TE Forwarding Adjacency (required)

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

1. enable

2. configure terminal

3. interface tunnel number

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface tunnel number

Example:

Router(config)interface tunnel 0

Designates a tunnel interface for the forwarding adjacency.

Configuring MPLS TE Forwarding Adjacency

To configure an MPLS TE forwarding adjacency, use the following command in interface configuration mode:

Command
Purpose

Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency {holdtime value}

Advertises a TE tunnel as a link in an IGP network.


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.


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:

Command
Purpose

Router(config-if)# isis metric default-metric {level-1 | level-2}

Configures the cost metric for a tunnel interface to be used as a forwarding adjacency.

Note You should configure the isis metric command with level 1 or 2 to be consistent with the IGP level at which you are performing traffic engineering. Otherwise, the metric has the default value of 10.


Verifying MPLS TE Forwarding Adjacency

To verify MPLS TE forwarding adjacency configuration, use this procedure:


Step 1 Use the show mpls traffic-eng forwarding-adjacency command to see the current tunnels:

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)

Monitoring and Maintaining MPLS TE Forwarding Adjacency

To monitor and maintain an MPLS TE forwarding adjacency, use the following commands in EXEC mode:

Command
Purpose

Router# show mpls traffic-eng forwarding-adjacency

Displays information about traffic engineering tunnels.

Router# show isis area-tag database [level-1] [level-2] [l1] [l2] [detail] [lspid]

Displays information about the IS-IS link-state database.


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 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

Here is sample output in which a forwarding adjacency has been configured:

Router# show run

Building configuration...
Current configuration :364 bytes
!
interface Tunnel7
 ip unnumbered Loopback0
 no ip directed-broadcast
 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
 isis metric 2 level 1

Note Do not use the tunnel mpls traffic-eng autoroute announce statement in your configuration when you are using forwarding adjacency.


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

Related Topic
Document Title

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

Standard
Title

None


MIBs

MIB
MIBs Link

None

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

None


Technical Assistance

Description
Link

The Cisco Technical Support & Documentation website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport


Command Reference

This section documents modified commands only.

debug mpls traffic-eng forwarding-adjacency

show mpls traffic-eng forwarding-adjacency

tunnel mpls traffic-eng forwarding-adjacency

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

Release
Modification

12.0(15)S

This command was introduced.

12.0(16)ST

This command was integrated into Cisco IOS Release 12.0(16)ST.

12.2(18)S

This command was integrated into Cisco IOS Release 12.2(18)S.

12.2(18)SXD

This command was integrated into Cisco IOS Release 12.2(18)SX.

12.2(27)SBC.

This command was integrated into Cisco IOS Release 12.2(27)SBC.

12.2(28)SB

This command was integrated into Cisco IOS Release 12.2(28)SB.


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-adjacency

MPLS traffic-eng debugging is on

With a tunnel configured, the following output appears:

interface Tunnel0
 ip unnumbered Loopback0
 no ip directed-broadcast
 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 dynamic
end

When 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

Command
Description

show debug

Displays active debug output.

show mpls traffic-eng forwarding-adjacency

Displays TE tunnels being advertised as links in an IGP network.

tunnel mpls traffic-eng forwarding-adjacency

Advertises a TE tunnel as a link in an IGP network.


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

ip address

(Optional) Destination address for forwarding-adjacency tunnels.


Defaults

No default behavior or values.

Command Modes

EXEC

Command History

Release
Modification

12.0(15)S

This command was introduced.

12.0(16)ST

This command was integrated into Cisco IOS Release 12.0(16)ST.

12.2(18)S

This command was integrated into Cisco IOS Release 12.2(18)S.

12.2(18)SXD

This command was integrated into Cisco IOS Release 12.2(18)SX.

12.2(27)SBC

This command was integrated into Cisco IOS Release 12.2(27)SBC.

12.2(28)SB

This command was integrated into Cisco IOS Release 12.2(28)SB.


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 run

Building configuration...
Current configuration :364 bytes
!
interface Tunnel7
 ip unnumbered Loopback0
 no ip directed-broadcast
 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
 isis metric 2 level 1
end

Use the show mpls traffic-eng forwarding-adjacency command again to see the current tunnels:

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)

Related Commands

Command
Description

debug mpls traffic-eng forwarding-adjacency

Displays debug messages for traffic-engineering, forwarding-adjacency events.

tunnel mpls traffic-eng forwarding-adjacency

Advertises a TE tunnel as a link in an IGP network.


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

Release
Modification

12.0(15)S

This command was introduced.

12.0(16)ST

This command was integrated into Cisco IOS Release 12.0(16)ST.

12.2(18)S

This command was integrated into Cisco IOS Release 12.2(18)S.

12.2(18)SXD

This command was integrated into Cisco IOS Release 12.2(18)SX.

12.2(27)SBC

This command was integrated into Cisco IOS Release 12.2(27)SBC.

12.2(28)SB

This command was integrated into Cisco IOS Release 12.2(28)SB.


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 The tunnel mpls traffic-eng forwarding-adjacency command requires IS-IS support.


Examples

In the following example, the holdtime is set to 10,000 milliseconds:

Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency holdtime 10000

In the following example, the holdtime defaults to 0:

Router(config-if)# tunnel mpls traffic-eng forwarding-adjacency

Related Commands

Command
Description

debug mpls traffic-eng forwarding-adjacency

Displays debug messages for traffic engineering, forwarding-adjacency events.

isis metric

Configures the cost metric for an interface.

show mpls traffic-eng forwarding-adjacency

Displays TE tunnels being advertised as links in an IGP network.


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 See Internetworking Terms and Acronyms for terms not included in this glossary.