MPLS Traffic Engineering: Shared Risk Link Groups

First Published: May 6, 2004
Last Updated: July 11, 2008

The MPLS Traffic Engineering: Shared Risk Link Groups feature enhances backup tunnel path selection so that a backup tunnel avoids using links that are in the same Shared Risk Link Group (SRLG) as interfaces the backup tunnel is protecting.

SRLGs refer to situations where links in a network share a common fiber (or a common physical attribute). If one link fails, other links in the group may fail too. Links in the group have a shared risk.

This document contains information about and instructions for configuring the MPLS Traffic Engineering: Shared Risk Link Groups feature.

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Contents

•Prerequisites for MPLS Traffic Engineering: Shared Risk Link Groups

•Restrictions for MPLS Traffic Engineering: Shared Risk Link Groups

•Information About MPLS Traffic Engineering: Shared Risk Link Groups

•How to Configure MPLS Traffic Engineering: Shared Risk Link Groups

•Configuration Examples for MPLS Traffic Engineering: Shared Risk Link Groups

•Additional References

•Feature Information for MPLS Traffic Engineering: Shared Risk Link Groups

•Glossary

Prerequisites for MPLS Traffic Engineering: Shared Risk Link Groups

•You must configure Fast Reroutable tunnels.

•You must enable the autotunnel backup.

Restrictions for MPLS Traffic Engineering: Shared Risk Link Groups

•The backup tunnel must be within a single area.

•Manually created backup tunnels do not automatically avoid SRLGs of protected interfaces.

•A primary tunnel cannot be specified to avoid links belonging to specified SRLGS.

Information About MPLS Traffic Engineering: Shared Risk Link Groups

•MPLS Traffic Engineering Brief Overview

•MPLS Traffic Engineering Shared Risk Link Groups

•Fast Reroute Protection for MPLS TE SRLGs

•Autotunnel Backup for MPLS TE SRLGs

MPLS Traffic Engineering Brief Overview

Multiprotocol Label Switching (MPLS) is an Internet Engineering Task Force (IETF)-specified framework that provides for the efficient designation, routing, forwarding, and switching of traffic flows through the network.

Traffic engineering (TE) is the process of adjusting bandwidth allocations to ensure that enough is left for high-priority traffic.

In MPLS TE, the upstream router creates a network tunnel for a particular traffic stream, then fixes the bandwidth available for that tunnel.

MPLS Traffic Engineering Shared Risk Link Groups

SRLGs refer to situations where links in a network share a common fiber (or a common physical attribute). If one link fails, other links in the group may fail too. Links in the group have a shared risk.

Backup tunnels should avoid using links in the same SRLG as interfaces they are protecting. Otherwise, when the protected link fails the backup tunnel fails too.

Figure 1 shows a primary label-switched path (LSP) from router R1 to router R5. The LSP protects against the failure of the R2-R3 link at R2 via a backup tunnel to R4. If the R2-R3 link fails, link protection reroutes the LSP along the backup tunnel. However, the R2-R3 link and one of the backup tunnel links are in the same SRLG. So if the R2-R3 link fails, the backup tunnel may fail too.

Figure 1 Backup Tunnel in the Same SRLG as the Interface It Is Protecting

The MPLS TE SRLG feature enhances backup tunnel path selection so a backup tunnel can avoid using links that are in the same SRLG as the interfaces it is protecting.

There are two ways for a backup tunnel to avoid the SRLGs of its protected interface:

•The router does not create the backup tunnel unless it avoids SRLGs of the protected interface.

•The router tries to avoid SRLGs of the protected interface, but if that is not possible the router creates the backup tunnel anyway. In this case there are two explicit paths. The first explicit path tries to avoid the SRLGs of the protected interface. If that does not work, the backup tunnel uses the second path (which ignores SRLGs).

Note Only backup tunnels that routers create automatically (called autotunnel backup) can avoid SRLGs of protected interfaces. For more information about these backup tunnels, see the "Autotunnel Backup for MPLS TE SRLGs" section.

To activate the MPLS TE SRLG feature, you must do the following:

•Configure the SRLG membership of each link that has a shared risk with another link.

•Configure the routers to automatically create backup tunnels that avoid SRLGs of the protected interfaces.

For a detailed explanation of the configuration steps, see the "How to Configure MPLS Traffic Engineering: Shared Risk Link Groups" section.

Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS-IS) flood the SRLG membership information (including other TE link attributes such as bandwidth availability and affinity) so that all routers in the network have the SRLG information for each link. With this topology information, routers can compute backup tunnel paths that exclude links having SRLGs in common with their protected interfaces. As shown in Figure 2, the backup tunnel avoids the link between R2 and R3, which shares an SRLG with the protected interface.

Figure 2 Backup Tunnel That Avoids SRLG of Protected Interface

Fast Reroute Protection for MPLS TE SRLGs

Fast Reroute (FRR) protects MPLS TE LSPs from link and node failures by locally repairing the LSPs at the point of failure. This protection allows data to continue to flow on LSPs while their headend routers attempt to establish new end-to-end LSPs to replace them. FRR locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or nodes.

Backup tunnels that bypass only a single link of the LSP's path provide link protection. They protect LSPs if a link along their path fails by rerouting the LSP's traffic to the next hop (bypassing the failed link). These are referred to as next-hop (NHOP) backup tunnels because they terminate at the LSP's next hop beyond the point of failure. Figure 3 illustrates an NHOP backup tunnel.

Figure 3 NHOP Backup Tunnel

FRR provides node protection for LSPs. Backup tunnels that bypass next-hop nodes along LSP paths are called next-next-hop (NNHOP) backup tunnels because they terminate at the node following the next-hop node of the LSP paths, thereby bypassing the next-hop node. They protect LSPs if a node along their path fails by enabling the node upstream of the failure to reroute the LSPs and their traffic around the failed node to the next-next hop. FRR supports the use of Resource Reservation Protocol (RSVP) hellos to accelerate the detection of node failures. NNHOP backup tunnels also provide protection from link failures, because they bypass the failed link and the node.

Figure 4 illustrates an NNHOP backup tunnel.

Figure 4 NNHOP Backup Tunnel

Autotunnel Backup for MPLS TE SRLGs

Autotunnel backup is the ability of routers to create backup tunnels automatically. Therefore, you do not need to preconfigure each backup tunnel and then assign the backup tunnel to the protected interface. Only automatically created backup tunnels can avoid SRLGs or their protected interfaces.

For information about backup tunnels, see the "Fast Reroute Protection for MPLS TE SRLGs" section.

For detailed information about autotunnel backup and how you can change the default command values, see MPLS Traffic Engineering (TE)--AutoTunnel Primary and Backup.

To globally activate the autotunnel backup feature, enter the mpls traffic-eng auto-tunnel backup command.

Figure 5 illustrates an NNHOP automatically generated backup tunnel that excludes the router 192.168.1.1 and terminates at router R4. The backup tunnel must avoid touching any links of 192.168.1.1.

Figure 5 Autotunnel Backup for NNHOP

Figure 6 illustrates an NHOP automatically generated backup tunnel that terminates at router R3 and avoids the link 10.1.1.1, not the entire node.

Figure 6 Autotunnel Backup for NHOP

Note NNHOP excludes the router ID (the entire router must be excluded; that is, no link of the router can be included in the backup tunnel's path). NHOP excludes only the link when the backup tunnel's path is computed.

How to Configure MPLS Traffic Engineering: Shared Risk Link Groups

•Configuring MPLS TE SRLG Membership of Each Link That Has a Shared Risk with Another Link (required)

•Configuring the Routers That Automatically Create Backup Tunnels to Avoid MPLS TE SRLGs of Their Protected Interfaces (required)

•Verifying the MPLS Traffic Engineering: Shared Risk Link Groups Configuration (optional)

Configuring MPLS TE SRLG Membership of Each Link That Has a Shared Risk with Another Link

Perform the following task to configure MPLS TE SRLG membership of each link that has a shared risk with another link. Configuring SRLG membership enhances backup tunnel path selection so that a backup tunnel avoids using links that are in the same SRLG as interfaces the backup tunnel is protecting.

Enter the commands on the physical interface.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type slot/port

4. mpls traffic-eng srlg [number]

5. end

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 type slot/port

Example:

Router(config)# interface pos 1/1

Specifies an interface and enters interface configuration mode.

•The type argument is the type of interface to be configured.

•The slot argument is the slot number. Refer to the appropriate hardware manual for slot and port information.

•The /port argument is the port number. Refer to the appropriate hardware manual for slot and port information. The slash (/) is required.

Step 4 

mpls traffic-eng srlg [number]

Example:

Router(config-if)# mpls traffic-eng srlg 5

Configures the SRLG membership of a link (interface).

•The number argument is an SRLG identifier. Valid values are 0 to 4,294,967,295.

Note To make the link a member of multiple SRLGs, enter the mpls traffic-eng srlg command multiple times.

Step 5 

end

Example:

Router(config-if)# end

Exits to privileged EXEC mode.

Configuring the Routers That Automatically Create Backup Tunnels to Avoid MPLS TE SRLGs of Their Protected Interfaces

Perform the following task to configure routers that automatically create backup tunnels to avoid MPLS TE SRLGs of their protected interfaces. Backup tunnels provide link protection by rerouting traffic to the next hop bypassing failed links or in this instance by avoiding SRLGs.

SUMMARY STEPS

1. enable

2. configure terminal

3. mpls traffic-eng auto-tunnel backup srlg exclude [force | preferred]

4. end

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 

mpls traffic-eng auto-tunnel backup srlg exclude [force | preferred]

Example:

Router(config)# mpls traffic-eng auto-tunnel backup srlg exclude force

Specifies that autocreated backup tunnels should avoid SRLGs of its protected interface.

•The force keyword forces the backup tunnel to avoid SRLGs of its protected interface or interfaces.

•The preferred keyword causes the backup tunnel to try to avoid SRLGs of its protected interface or interfaces, but the backup tunnel can be created if SRLGs cannot be avoided.

Step 4 

end

Example:

Router(config)# end

Returns to privileged EXEC mode.

Verifying the MPLS Traffic Engineering: Shared Risk Link Groups Configuration

SUMMARY STEPS

1. enable

2. show running-config

3. show mpls traffic-eng link-management interfaces interface slot/port

4. show mpls traffic-eng topology

5. show mpls traffic-eng topology srlg

6. show mpls traffic-eng topology brief

7. show mpls traffic-eng link-management advertisements

8. show ip rsvp fast-reroute

9. mpls traffic-eng auto-tunnel backup srlg exclude force

10. show ip explicit-paths

11. show mpls traffic-eng tunnels tunnel num

12. mpls traffic-eng auto-tunnel backup srlg exclude preferred

13. show ip explicit-paths

14. show ip rsvp fast-reroute

15. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. Enter your password, if prompted. For example: 

Router> enable

Router#

 
   
 
    
   
 Step 2 show running config 
 
    
   
 Use the following commands to configure the SRLG membership of the interface pos 3/1 and to verify that the configuration is as expected. For example: 
 
    
   
 
    
Router# configure terminal 

 
   
 
    
   
 
    
Router(config)# interface pos 3/1 

 
   
 
    
   
 
    
Router(config-if)# mpls traffic-eng srlg 1 

 
   
 
    
   
 
    
Router(config-if)# mpls traffic-eng srlg 2 

 
   
 
    
   
 
    
Router(config-if)# end

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Router# show running-config 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
interface POS 3/1

 
   
 
    
   
 
    
 ip address 10.0.0.33 255.255.255.255

 
   
 
    
   
 
    
 no ip directed-broadcast

 
   
 
    
   
 
    
 ip router isis

 
   
 
    
   
 
    
 encapsulation ppp

 
   
 
    
   
 
    
 no ip mroute-cache

 
   
 
    
   
 
    
 mpls traffic-eng tunnels

 
   
 
    
   
 
    
 mpls traffic-eng backup-path Tunnel5000

 
   
 
    
   
 
    
 mpls traffic-eng srlg 1

 
   
 
    
   
 
    
 mpls traffic-eng srlg 2

 
   
 
    
   
 
    
 tag-switching ip

 
   
 
    
   
 
    
 crc 32

 
   
 
    
   
 
    
 clock source internal

 
   
 
    
   
 
    
 pos ais-shut

 
   
 
    
   
 
    
 pos report rdool

 
   
 
    
   
 
    
 pos report lais

 
   
 
    
   
 
    
 pos report lrdi

 
   
 
    
   
 
    
 pos report pais

 
   
 
    
   
 
    
 pos report prdi

 
   
 
    
   
 
    
 pos report sd-ber

 
   
 
    
   
 
    
 isis circuit-type level-2-only

 
   
 
    
   
 
    
 ip rsvp bandwidth 20000 20000 sub-pool 5000

 
   
 
    
   
 
    
 
   
 
    
   
 This verifies that the Packet over SONET (POS) interface pos 3/1 is associated that SRLG 1 and SRLG 2. 
 
    
   
 Step 3 show mpls traffic-eng link-management interfaces interface slot/port 
 
    
   
 Use this command to show the SRLG membership configured on interface pos 3/1. For example: 
 
    
   
 
    
Router# show mpls traffic-eng link-management interfaces pos 3/1 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
System Information::

 
   
 
    
   
 
    
    Links Count:         11

 
   
 
    
   
 
    
Link ID:: PO3/1 (10.0.0.33)

 
   
 
    
   
 
    
    Link Status:

 
   
 
    
   
 
    
      SRLGs:               1 2

 
   
 
    
   
 
    
      Physical Bandwidth:  2488000 kbits/sec

 
   
 
    
   
 
    
      Max Res Global BW:   20000 kbits/sec (reserved:0% in, 0% out)

 
   
 
    
   
 
    
      Max Res Sub BW:      5000 kbits/sec (reserved:0% in, 0% out)

 
   
 
    
   
 
    
      MPLS TE Link State:  MPLS TE on, RSVP on, admin-up, flooded

 
   
 
    
   
 
    
      Inbound Admission:   allow-all

 
   
 
    
   
 
    
      Outbound Admission:  allow-if-room

 
   
 
    
   
 
    
      Admin. Weight:       10 (IGP)

 
   
 
    
   
 
    
      IGP Neighbor Count:  1

 
   
 
    
   
 
    
      IGP Neighbor:        ID 0000.0000.0004.00, IP 10.0.0.34 (Up)

 
   
 
    
   
 
    
    Flooding Status for each configured area [1]:

 
   
 
    
   
 
    
      IGP Area[1]: isis  level-2: flooded

 
   
 
    
   
 
    
 
   
 
    
   
 Step 4 show mpls traffic-eng topology 
 
    
   
 Use this command to show the SRLG link membership flooded via the Interior Gateway Protocol (IGP). For example: 
 
    
   
 
    
Router# show mpls traffic-eng topology 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
My_System_id:0000.0000.0003.00 (isis  level-2)

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Signalling error holddown:10 sec Global Link Generation 9

 
   
 
    
   
 
    
 
   
 
    
   
 
    
IGP Id:0000.0000.0003.00, MPLS TE Id:10.0.3.1 Router Node  (isis

 
   
 
    
   
 
    
level-2)

 
   
 
    
   
 
    
      link[0]:Point-to-Point, Nbr IGP Id:0000.0000.0004.00,

 
   
 
    
   
 
    
nbr_node_id:2, gen:9

 
   
 
    
   
 
    
          frag_id 0, Intf Address:10.0.0.33, Nbr Intf Address:10.0.0.34

 
   
 
    
   
 
    
          TE metric:10, IGP metric:10, attribute_flags:0x0

 
   
 
    
   
 
    
          SRLGs:1 2

 
   
 
    
   
 
    
          physical_bw:2488000 (kbps), max_reservable_bw_global:20000

 
   
 
    
   
 
    
(kbps)

 
   
 
    
   
 
    
          max_reservable_bw_sub:5000 (kbps)

 
   
 
    
   
 
    
 
   
 
    
   
 
    
                                 Global Pool       Sub Pool

 
   
 
    
   
 
    
               Total Allocated   Reservable        Reservable

 
   
 
    
   
 
    
               BW (kbps)         BW (kbps)         BW (kbps)

 
   
 
    
   
 
    
               ---------------   -----------       ----------

 
   
 
    
   
 
    
        bw[0]:           0            20000             5000

 
   
 
    
   
 
    
        bw[1]:           0            20000             5000

 
   
 
    
   
 
    
        bw[2]:           0            20000             5000

 
   
 
    
   
 
    
        bw[3]:           0            20000             5000

 
   
 
    
   
 
    
        bw[4]:           0            20000             5000

 
   
 
    
   
 
    
        bw[5]:           0            20000             5000

 
   
 
    
   
 
    
 
   
 
    
   
 Step 5 show mpls traffic-eng topology srlg 
 
    
   
 Use this command to display all the links in the network that are members of a given SRLG. For example: 
 
    
   
 
    
Router# show mpls traffic-eng topology srlg

 
   
 
    
   
 
    
 
   
 
    
   
 
    
MPLS TE Id:0000.0000.0003.00 (isis  level-2)

 
   
 
    
   
 
    
  SRLG:1

 
   
 
    
   
 
    
     10.0.0.33

 
   
 
    
   
 
    
  SRLG:2

 
   
 
    
   
 
    
     10.0.0.33

 
   
 
    
   
 
    
 
   
 
    
   
 The following command shows that there are two links in SRLG 1: 
 
    
   
 
    
Router# show mpls traffic-eng topology srlg

 
   
 
    
   
 
    
 
   
 
    
   
 
    
MPLS TE Id:0000.0000.0003.00 (isis  level-2)

 
   
 
    
   
 
    
  SRLG:1

 
   
 
    
   
 
    
     10.0.0.33

 
   
 
    
   
 
    
     10.0.0.49

 
   
 
    
   
 
    
 
   
 
    
   
 Step 6 show mpls traffic-eng topology brief 
 
    
   
 Use this command to display brief topology information: 
 
    
   
 
    
Router# show mpls traffic-eng topology brief

 
   
 
    
   
 
    
 
   
 
    
   
 
    
My_System_id:0000.0000.0003.00 (isis  level-2)

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Signalling error holddown:10 sec Global Link Generation 9

 
   
 
    
   
 
    
 
   
 
    
   
 
    
IGP Id:0000.0000.0003.00, MPLS TE Id:10.0.3.1 Router Node  (isis

 
   
 
    
   
 
    
level-2)

 
   
 
    
   
 
    
      link[0]:Point-to-Point, Nbr IGP Id:0000.0000.0004.00,

 
   
 
    
   
 
    
nbr_node_id:2, gen:9

 
   
 
    
   
 
    
          frag_id 0, Intf Address:10.0.0.33, Nbr Intf Address:10.0.0.34

 
   
 
    
   
 
    
          TE metric:10, IGP metric:10, attribute_flags:0x0

 
   
 
    
   
 
    
          SRLGs:1 2

 
   
 
    
   
 
    
 
   
 
    
   
 Step 7 show mpls traffic-eng link-management advertisements 
 
    
   
 Use this command to show local link information that MPLS TE link management is currently flooding into the global TE topology. For example: 
 
    
   
 
    
Router# show mpls traffic-eng link-management advertisements 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Flooding Status:      ready

 
   
 
    
   
 
    
Configured Areas:     1

 
   
 
    
   
 
    
IGP Area[1] ID::  isis  level-2

 
   
 
    
   
 
    
  System Information::

 
   
 
    
   
 
    
    Flooding Protocol:    ISIS

 
   
 
    
   
 
    
  Header Information::

 
   
 
    
   
 
    
    IGP System ID:        0000.0000.0003.00

 
   
 
    
   
 
    
    MPLS TE Router ID:    10.0.3.1

 
   
 
    
   
 
    
    Flooded Links:        2

 
   
 
    
   
 
    
  Link ID::  0

 
   
 
    
   
 
    
    Link Subnet Type:     Point-to-Point

 
   
 
    
   
 
    
    Link IP Address:      10.0.0.49

 
   
 
    
   
 
    
    IGP Neighbor:         ID 0000.0000.0007.00, IP 10.0.0.50

 
   
 
    
   
 
    
    TE metric:            80000

 
   
 
    
   
 
    
    IGP metric:           80000

 
   
 
    
   
 
    
    SRLGs:                None

 
   
 
    
   
 
    
    Physical Bandwidth:   622000 kbits/sec

 
   
 
    
   
 
    
    Res. Global BW:       20000 kbits/sec

 
   
 
    
   
 
    
    Res. Sub BW:          5000 kbits/sec

 
   
 
    
   
 
    
    Downstream::

 
   
 
    
   
 
    
                                Global Pool   Sub Pool

 
   
 
    
   
 
    
                                -----------   --------------

 
   
 
    
   
 
    
      Reservable Bandwidth[0]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[1]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[2]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[3]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[4]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[5]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[6]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[7]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
    Attribute Flags:      0x00000000

 
   
 
    
   
 
    
  Link ID::  1

 
   
 
    
   
 
    
    Link Subnet Type:     Point-to-Point

 
   
 
    
   
 
    
    Link IP Address:      10.0.0.33

 
   
 
    
   
 
    
    IGP Neighbor:         ID 0000.0000.0004.00, IP 10.0.0.34

 
   
 
    
   
 
    
    TE metric:            10

 
   
 
    
   
 
    
    IGP metric:           10

 
   
 
    
   
 
    
    SRLGs:                1

 
   
 
    
   
 
    
    Physical Bandwidth:   2488000 kbits/sec

 
   
 
    
   
 
    
    Res. Global BW:       20000 kbits/sec

 
   
 
    
   
 
    
    Res. Sub BW:          5000 kbits/sec

 
   
 
    
   
 
    
    Downstream::

 
   
 
    
   
 
    
                                Global Pool   Sub Pool

 
   
 
    
   
 
    
                                -----------   --------------

 
   
 
    
   
 
    
      Reservable Bandwidth[0]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[1]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[2]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[3]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[4]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[5]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[6]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
      Reservable Bandwidth[7]:  20000         5000 kbits/sec

 
   
 
    
   
 
    
    Attribute Flags:      0x00000000

 
   
 
    
   
 
    
 
   
 
    
   
 Step 8 show ip rsvp fast-reroute 
 
    
   
 Use this command to show that the primary tunnel is going over Pos3/1 on R3, on which SLRG 1 is configured. For example: 
 
    
   
 
    
Router# show ip rsvp fast-reroute 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Primary    Protect      BW      Backup

 
   
 
    
   
 
    
Tunnel     I/F        BPS:Type  Tunnel:Label  State   Level   Type

 
   
 
    
   
 
    
-------    -------    --------  ------------  -----   -----   ----

 
   
 
    
   
 
    
R3-PRP_t0  PO3/1 0:G  None      None          None    None    None

 
   
 
    
   
 
    
 
   
 
    
   
 Step 9 mpls traffic-eng auto-tunnel backup srlg exclude force 
 
    
   
 Use the following commands to configure autotunnel backup with the force keyword. For example: 
 
    
   
 
    
Router# configure terminal 

 
   
 
    
   
 
    
Router(config)# mpls traffic-eng auto-tunnel backup 

 
   
 
    
   
 
    
Router(config)# mpls traffic-eng auto-tunnel backup srlg exclude force 

 
   
 
    
   
 
    
Router(config)# exit

 
   
 
    
   
 
    
 
   
 
    
   
 Step 10 show ip explicit-paths 
 
    
   
 Use the following command to verify that the force keyword is configured with the pos3/1 link excluded from the IP explicit path. For example: 
 
    
   
 
    
Router# show ip explicit-paths 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
PATH __dynamic_tunnel65436 (loose source route, path complete,

 
   
 
    
   
 
    
generation 24, status non-configured)

 
   
 
    
   
 
    
    1:exclude-address 10.0.0.33

 
   
 
    
   
 
    
    2:exclude-srlg    10.0.0.33

 
   
 
    
   
 
    
 
   
 
    
   
 Step 11 show mpls traffic-eng tunnels tunnel num 
 
    
   
 Use the following command to show that autotunnel backup is configured but is down because the headend router does not have any other path to signal and it cannot use pos2/1 because it belongs in the same SRLG; that is, SRLG 1. For example: 
 
    
   
 
    
Router# show mpls traffic-eng tunnels tunnel 65436

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Name:R3-PRP_t65436                       (Tunnel65436) Destination:

 
   
 
    
   
 
    
10.0.4.1

 
   
 
    
   
 
    
  Status:

 
   
 
    
   
 
    
    Admin:up         Oper:down   Path:not valid   Signalling:Down

 
   
 
    
   
 
    
    path option 1, type explicit __dynamic_tunnel65436

 
   
 
    
   
 
    
 
   
 
    
   
 
    
  Config Parameters:

 
   
 
    
   
 
    
    Bandwidth:0        kbps (Global)  Priority:7  7   Affinity:

 
   
 
    
   
 
    
0x0/0xFFFF

 
   
 
    
   
 
    
    Metric Type:TE (default)

 
   
 
    
   
 
    
    AutoRoute: disabled  LockDown:disabled  Loadshare:0

 
   
 
    
   
 
    
bw-based

 
   
 
    
   
 
    
    auto-bw:disabled

 
   
 
    
   
 
    
 
   
 
    
   
 
    
  Shortest Unconstrained Path Info:

 
   
 
    
   
 
    
    Path Weight:10 (TE)

 
   
 
    
   
 
    
    Explicit Route:10.0.0.34 10.0.4.1

 
   
 
    
   
 
    
  History:

 
   
 
    
   
 
    
    Tunnel:

 
   
 
    
   
 
    
      Time since created:5 minutes, 29 seconds

 
   
 
    
   
 
    
    Path Option 1:

 
   
 
    
   
 
    
      Last Error:PCALC::No path to destination, 0000.0000.0004.00

 
   
 
    
   
 
    
 
   
 
    
   
 Step 12 mpls traffic-eng auto-tunnel backup srlg exclude preferred 
 
    
   
 The following commands configure autotunnel backup with the preferred keyword. For example: 
 
    
   
 
    
Router# configure terminal

 
   
 
    
   
 
    
Router(config)# mpls traffic-eng auto-tunnel backup 

 
   
 
    
   
 
    
Router(config)# mpls traffic-eng auto-tunnel backup srlg exclude preferred

 
   
 
    
   
 
    
Router(config)# exit

 
   
 
    
   
 
    
 
   
 
    
   
 Step 13 show ip explicit-paths  
 
    
   
 The following command shows two explicit paths. The first path avoids the SRLGs of the protected interface. The second path does not avoid the SRLGs. For example: 
 
    
   
 
    
Router# show ip explicit-paths 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
PATH __dynamic_tunnel65436 (loose source route, path complete,

 
   
 
    
   
 
    
generation 30, status non-configured)

 
   
 
    
   
 
    
    1:exclude-address 10.0.0.33

 
   
 
    
   
 
    
    2:exclude-srlg    10.0.0.33

 
   
 
    
   
 
    
PATH __dynamic_tunnel65436_pathopt2 (loose source route, path complete,

 
   
 
    
   
 
    
generation 33, status non-configured)

 
   
 
    
   
 
    
    1:exclude-address 10.0.0.33

 
   
 
    
   
 
    
 
   
 
    
   
 Step 14 show ip rsvp fast-reroute 
 
    
   
 The following command shows that the primary tunnel is protected with autotunnel backup using the second path option (see Step 10) that does not avoid the SRLGs. For example: 
 
    
   
 
    
Router# show ip rsvp fast-reroute 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Primary    Protect      BW      Backup

 
   
 
    
   
 
    
Tunnel     I/F        BPS:Type  Tunnel:Label  State   Level   Type

 
   
 
    
   
 
    
-------    -------    --------  ------------  -----   -----   ----

 
   
 
    
   
 
    
R3-PRP_t0  PO3/1 0:G  0:G       Tu65436:0     Ready   any-unl nhop

 
   
 
    
   
 
    
 
   
 
    
   
 The following command shows the path options for the tunnel Tu65436: 
 
    
   
 
    
Router# show mpls traffic-eng tunnels tunnel 65436 

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Name:R3-PRP_t65436                       (Tunnel65436) Destination:

 
   
 
    
   
 
    
10.0.4.1

 
   
 
    
   
 
    
  Status:

 
   
 
    
   
 
    
    Admin:up         Oper:up     Path:valid       Signalling:connected

 
   
 
    
   
 
    
 
   
 
    
   
 
    
    path option 2, type explicit __dynamic_tunnel65436_pathopt2 (Basis

 
   
 
    
   
 
    
for Setup, path weight 80020)

 
   
 
    
   
 
    
    path option 1, type explicit __dynamic_tunnel65436

 
   
 
    
   
 
    
  Config Parameters:

 
   
 
    
   
 
    
    Bandwidth:0        kbps (Global)  Priority:7  7   Affinity:

 
   
 
    
   
 
    
0x0/0xFFFF

 
   
 
    
   
 
    
    Metric Type:TE (default)

 
   
 
    
   
 
    
    AutoRoute: disabled  LockDown:disabled  Loadshare:0

 
   
 
    
   
 
    
bw-based

 
   
 
    
   
 
    
    auto-bw:disabled

 
   
 
    
   
 
    
  Active Path Option Parameters:

 
   
 
    
   
 
    
    State:explicit path option 2 is active

 
   
 
    
   
 
    
    BandwidthOverride:disabled  LockDown:disabled  Verbatim:disabled

 
   
 
    
   
 
    
 
   
 
    
   
 
    
InLabel  : -

 
   
 
    
   
 
    
  OutLabel :POS2/1, 23

 
   
 
    
   
 
    
  RSVP Signalling Info:

 
   
 
    
   
 
    
       Src 10.0.3.1, Dst 10.0.4.1, Tun_Id 65436, Tun_Instance 3

 
   
 
    
   
 
    
    RSVP Path Info:

 
   
 
    
   
 
    
      My Address:10.0.3.1

 
   
 
    
   
 
    
      Explicit Route:10.0.0.50 10.0.0.66 10.0.0.113 10.0.4.1

 
   
 
    
   
 
    
      Record   Route:  NONE

 
   
 
    
   
 
    
      Tspec:ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits

 
   
 
    
   
 
    
    RSVP Resv Info:

 
   
 
    
   
 
    
      Record   Route:  NONE

 
   
 
    
   
 
    
      Fspec:ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits

 
   
 
    
   
 
    
  Shortest Unconstrained Path Info:

 
   
 
    
   
 
    
    Path Weight:10 (TE)

 
   
 
    
   
 
    
    Explicit Route:10.0.0.34 10.0.4.1

 
   
 
    
   
 
    
 
   
 
    
   
 Step 15 exit 
 
    
   
 Use this command to exit to user EXEC mode. For example: 
 
    
   
 
    
Router# exit

 
   
 
    
   
 
    
Router>

 
   
 
    
   
 
    
 
   
 
   
 
    
     
    
    
   
 Configuration Examples for MPLS Traffic Engineering: Shared Risk Link Groups 
 
    
   
 •Configuring the SRLG Membership of Each Link That Has a Shared Risk with Another Link: Example 
 
    
   
 •Configuring the Routers That Automatically Create Backup Tunnels to Avoid SRLGs of Their Protected Interfaces: Example 
 
     
    
    
   
 Configuring the SRLG Membership of Each Link That Has a Shared Risk with Another Link: Example 
 
    
   
 The following example shows how to specify that the SRLG membership of each link has a shared risk with another link. 
 
    
   
 As shown in Figure 7 and in the following commands: 
 
    
   
 •link R2-R3 = SRLG5 
 
    
   
 •link R2-R3 = SRLG6 
 
    
   
 •link R7-R4 = SRLG5 
 
    
   
 •link R1-R2 = SRLG6 
 
    
   
 
    
Router1# configure terminal

 
   
 
    
   
 
    
Router1# interface pos 1/0

 
   
 
    
   
 
    
Router1(config-if)# mpls traffic-eng srlg 6

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Router2# configure terminal

 
   
 
    
   
 
    
Router2# interface pos 1/1

 
   
 
    
   
 
    
Router2(config-if)# mpls traffic-eng srlg 5

 
   
 
    
   
 
    
Router2(config-if)# mpls traffic-eng srlg 6

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Router7# configure terminal

 
   
 
    
   
 
    
Router7# interface pos 3/0

 
   
 
    
   
 
    
Router7(config-if)# mpls traffic-eng srlg 5

 
   
 
    
    
   
 Figure 7 SRLG Membership 
 
    
   
 
 
   
 
     
   
 
   
 
 
     
    
    
   
 Configuring the Routers That Automatically Create Backup Tunnels to Avoid SRLGs of Their Protected Interfaces: Example 
 
    
   
 The following example shows how to specify that automatically created backup tunnels are forced to avoid SRLGs of their protected interfaces: 
 
    
   
 
    
Router# configure terminal

 
   
 
    
   
 
    
Router(config)# mpls traffic-eng auto-tunnel backup 

 
   
 
    
   
 
    
Router(config)# mpls traffic-eng auto-tunnel backup srlg exclude force 

 
   
 
    
    
   
 Figure 8 illustrates the automatically created NNHOP backup tunnel that would be created to avoid SRLGs of the protected interface if the following conditions exist: 
 
    
   
 The exclude address is 192.168.1.1. 
 
    
   
 The link at R2 has an IP address of 10.1.1.1. 
 
    
   
 The backup tunnel's explicit path avoids links that have a membership in the same SRLG as the link whose IP address is 10.1.1.1. 
 
    
    
   
 Figure 8 srlg exclude force—NNHOP Autobackup Tunnel 
 
    
   
 
 
   
 
     
   
 
   
 
 
    
    
   
 Figure 9 illustrates the automatically created NHOP backup tunnel that would be created. 
 
    
    
   
 Figure 9 srlg exclude force—NHOP Autobackup Tunnel 
 
    
   
 
 
   
 
     
   
 
   
 
 
     
    
    
   
 Additional References 
 
     
    
    
   
 Related Documents
 
   
 
    
 
      
      
      
 
        
        

          Related Topic 
        
 		 
        
        

          Document Title 
        
 		 
      
 
      
 
       
 Fast Reroute 
 		 
       
 MPLS TE: Link and Node Protection, with RSVP Hellos Support (with Fast Tunnel Interface Down Detection) 
 		 
      
 
      
 
       
 IS-IS 
 		 
       
 Integrated IS-IS Routing Protocol Overview 
 		 
      
 
      
 
       
 OSPF 
 		 
       
 Configuring OSPF 
 		 
      
 
      
 
       
 Autotunnel backups 
 		 
       
 MPLS Traffic Engineering AutoTunnel Primary and Backup 
 		 
      
 
      
    
 
   
 
   
 
   
 
 
     
    
   
 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 
        
 		 
      
 
      
 
       
 draft-ietf-isis-gmpls-extensions-16.txt 
 		 
       
 IS-IS Extensions in Support of Generalized MPLS 
 		 
      
 
      
    
 
   
 
   
 
   
 
 
     
    
    
   
 Technical Assistance
 
   
 
    
 
      
      
      
 
        
        

          Description 
        
 		 
        
        

          Link 
        
 		 
      
 
      
 
       
 The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. 
 
 To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. 
 
 Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. 
 		 
       
 http://www.cisco.com/techsupport  
 		 
      
 
      
    
 
   
 
   
 
   
 
 
     
    
    
    
   
 Feature Information for MPLS Traffic Engineering: Shared Risk Link Groups 
 
    
   
 Table 1 lists the release history for this feature. 
 
    
   
 Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation. 
 
    
   
 Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS 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 software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature. 
 
   
 
    
   
 
 
   
 
    
 
      
       
       
      
 Table 1 Feature Information for MPLS Traffic Engineering: Shared Risk Link Groups  
 
      
      
      
 
        
        

          Feature Name 
        
 		 
        
        

          Releases 
        
 		 
        
        

          Feature Information 
        
 		 
      
 
      
 
       
 MPLS Traffic Engineering: Shared Risk Link Groups 
 		 
       
 12.0(28)S
12.0(29)S
12.2(33)SRA
12.2(33)SXH
12.4(20)T 
 		 
       
 The MPLS Traffic Engineering: Shared Risk Link Groups feature enhances backup tunnel path selection so that a backup tunnel avoids using links that are in the same Shared Risk Link Group (SRLG) as interfaces the backup tunnel is protecting. 
 
 SRLGs refer to situations where links in a network share a common fiber (or a common physical attribute). If one link fails, other links in the group may fail too. Links in the group have a shared risk. 
 
 This document contains information about and instructions for configuring the MPLS Traffic Engineering: Shared Risk Link Groups feature 
 
 In 12.0(28)S, this feature was introduced. 
 
 In 12.0(29)S, support was added for Open Shortest Path First (OSPF). 
 
 In 12.2(33)SRA, this feature was integrated into a Cisco IOS 12.2SRA release 
 
 In 12.2(33)SXH, this feature was integrated into a Cisco IOS 12.2SXH release. 
 
 In 12.4(20)T, this feature was integrated into a Cisco IOS 12.4T release. 
 
 The following sections provide information about this feature: 
 
 •MPLS Traffic Engineering Brief Overview 
 		 
      
 
      
 
         
         
       
 •MPLS Traffic Engineering Shared Risk Link Groups 
 
 •Fast Reroute Protection for MPLS TE SRLGs 
 
 •Autotunnel Backup for MPLS TE SRLGs 
 
 •Configuring MPLS TE SRLG Membership of Each Link That Has a Shared Risk with Another Link 
 
 •Configuring the Routers That Automatically Create Backup Tunnels to Avoid MPLS TE SRLGs of Their Protected Interfaces 
 
 •Verifying the MPLS Traffic Engineering: Shared Risk Link Groups Configuration 
 
 The following commands were introduced or modified: mpls traffic-eng auto-tunnel backup srlg exclude, mpls traffic-eng srlg, show ip explicit-paths, show mpls traffic-eng link-management advertisements, show mpls traffic-eng link-management interfaces, and show mpls traffic-eng topology. 
 		 
      
 
      
    
 
   
 
   
 
   
 
 
     
    
    
    
    
   
 Glossary 
 
    
   
 Fast Reroute—A mechanism for protecting MPLS traffic engineering (TE) LSPs from link and node failure by locally repairing the LSPs at the point of failure. This protection allows data to continue to flow on them while their headend routers attempt to establish end-to-end LSPs to replace them. FRR locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or nodes. 
 
    
   
 hop—Passage of a data packet between two network nodes (for example, between two routers). 
 
    
   
 IGP—Interior Gateway Protocol. An Internet protocol used to exchange routing information within an autonomous system. 
 
    
   
 interface—A network connection. 
 
    
   
 IP address—A 32-bit address assigned to hosts using TCP/IP. An IP address belongs to one of five classes (A, B, C, D, or E) and is written as four octets separated by periods (dotted decimal format). Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, and the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address. 
 
    
   
 IP explicit path—A list of IP addresses, each representing a node or link in the explicit path. 
 
    
   
 IS-IS—Intermediate System-to-Intermediate System. OSI link-state hierarchal routing protocol based on DECnet Phase V routing, where intermediate system (IS) routers exchange routing information based on a single metric to determine the network topology. 
 
    
   
 LDP—Label Distribution Protocol. A standard protocol between MPLS-enabled routers to negotiate the labels (addresses) used to forward packets. 
 
    
   
 link—A point-to-point connection between adjacent nodes. 
 
    
   
 LSP—label-switched path. A path that is followed by a labeled packet over several hops, starting at an ingress LSR and ending at an egress LSR. 
 
    
   
 LSR—label switching router. A Layer 3 router that forwards a packet based on the value of a label encapsulated in the packet. 
 
    
   
 MPLS—Multiprotocol Label Switching. A method for forwarding packets (frames) through a network. It enables routers at the edge of a network to apply labels to packets. ATM switches or existing routers in the network core can switch packets according to the labels with minimal lookup overhead. 
 
    
   
 node—An endpoint of a network connection or a junction common to two or more lines in a network. Nodes can be interconnected by links, and serve as control points in the network. 
 
    
   
 OSPF—Open Shortest Path First. A link-state hierarchical Interior Gateway Protocol (IGP) routing algorithm, derived from the IS-IS protocol. OSPF features include least-cost routing, multipath routing, and load balancing. 
 
    
   
 router—A network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information. 
 
    
   
 router ID—Something by which a router originating a packet can be uniquely distinguished from all other routers; for example, an IP address from one of the router's interfaces. 
 
    
   
 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 used. 
 
    
   
 tunnel—A secure communication path between two peers, such as two routers. A traffic engineering tunnel is 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 could cause the tunnel to take. 
 
    
    
    
   
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 All other trademarks mentioned in this document or Website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0805R) 
 
    
    
    
   
 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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