Loop-Free Alternate Fast Reroute with L2VPN

The Loop-Free Alternate (LFA) Fast Reroute (FRR) with Layer 2 Virtual Private Network (L2VPN) feature minimizes packet loss due to link or node failure.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Restrictions for Loop-Free Alternate Fast Reroute with L2VPN

  • Load balancing is not supported
  • Time-division multiplexing (TDM) pseudowire is not supported
  • Virtual Private LAN Services (VPLS) is not supported
  • The Virtual Private Wire Services (VPWS) scale number might change

Information About Loop-Free Alternate Fast Reroute with L2VPN

L2VPN Over Loop-Free Alternate Fast Reroute

The Loop-Free Alternate (LFA) Fast Reroute (FRR) feature offers an alternative to the MPLS Traffic Engineering Fast Reroute feature to minimize packet loss due to link or node failure. It introduces LFA FRR support for L2VPNs and Virtual Private Wire Services (VPWS), providing the following benefits:

  • Same level of protection from traffic loss
  • Simplified configuration
  • Link and node protection
  • Link and path protection
  • LFA (loop-free alternate) paths
  • Support for both IP and Label Distribution Protocol (LDP) core

LFA FRR enables a backup route to avoid traffic loss if a network fails. The backup routes (repair paths) are precomputed and installed in the router as the backup for the primary paths. After the router detects a link or adjacent node failure, it switches to the backup path to avoid traffic loss.

How to Configure Loop-Free Alternate Fast Reroute with L2VPN

To enable loop-free alternate fast reroute support for L2VPNs and VPWS, you must configure LFA FRR for the routing protocol. No additional configuration tasks are necessary. See one of the following documents, depending on the routing protocol:

Verifying Loop-Free Alternate Fast Reroute with L2VPN

Use one or more of the following commands to verify the LFA FRR configuration:

SUMMARY STEPS

    1.    show ip cef network-prefix internal

    2.    show mpls infrastructure lfd pseudowire internal

    3.    show platform hardware pp active feature cef database ipv4 network-prefix


DETAILED STEPS
    Step 1   show ip cef network-prefix internal


    Example: 
    show ip cef 16.16.16.16 internal

    Displays entries in the Cisco Express Forwarding (CEF) Forwarding Information Base (FIB).
    Step 2   show mpls infrastructure lfd pseudowire internal


    Example: 
    show mpls infrastructure lfd pseudowire internal

    Displays information about the Label Forwarding Database (LFD) and pseudowires.
    Step 3   show platform hardware pp active feature cef database ipv4 network-prefix


    Example: 
    show platform hardware pp active feature cef database ipv4 16.16.16.16/32

    Displays information about the CEF database.

    Configuration Examples for Loop-Free Alternate Fast Reroute with L2VPN

    Example: Verifying LFA FRR with L2VPN

    show ip cef internal

    The following example shows the configuration of LFA FRR for OSPF:

    router ospf 1
 router-id 17.17.17.17
 fast-reroute per-prefix enable prefix-priority low
 network 3.3.3.0 0.0.0.255 area 1
 network 6.6.6.0 0.0.0.255 area 1
 network 7.7.7.0 0.0.0.255 area 1
 network 17.17.17.17 0.0.0.0 area 1

    show ip cef internal

    The following is sample output from the show ip cef internal command:

    Device# show ip cef 16.16.16.16 internal 
16.16.16.16/32, epoch 2, RIB[I], refcount 7, per-destination sharing
  sources: RIB, RR, LTE 
  feature space:
   IPRM: 0x00028000
   Broker: linked, distributed at 1st priority
   LFD: 16.16.16.16/32 1 local label
   local label info: global/17
        contains path extension list
        disposition chain 0x3A3C1DF0
        label switch chain 0x3A3C1DF0
  subblocks:
   1 RR source [no flags]
    non-eos chain [16|44]
  ifnums:
   GigabitEthernet0/0/2(9): 7.7.7.2
   GigabitEthernet0/0/7(14): 7.7.17.9
  path 35D61070, path list 3A388FA8, share 1/1, type attached nexthop, for IPv4, flags has-repair
    MPLS short path extensions: MOI flags = 0x20 label 16
  nexthop 7.7.7.2 GigabitEthernet0/0/2 label [16|44], adjacency IP adj out of GigabitEthernet0/0/2, addr 7.7.7.2 35E88520
    repair: attached-nexthop 7.7.17.9 GigabitEthernet0/0/7 (35D610E0)
  path 35D610E0, path list 3A388FA8, share 1/1, type attached nexthop, for IPv4, flags repair, repair-only
  nexthop 7.7.17.9 GigabitEthernet0/0/7, repair, adjacency IP adj out of GigabitEthernet0/0/7, addr 7.7.17.9 3A48A4E0
  output chain: label [16|44]
  FRR Primary (0x35D10F60)
  <primary:  TAG adj out of GigabitEthernet0/0/2, addr 7.7.7.2 35E88380>
  <repair:  TAG adj out of GigabitEthernet0/0/7, addr 7.7.17.9 3A48A340>
Rudy17#show mpls infrastructure lfd pseudowire internal
PW ID: 1VC ID: 4, Nexthop address: 16.16.16.16
SSM Class: SSS HW
Segment Count: 1
VCCV Types Supported:  cw ra ttl
Imposition details:
 Label stack {22 16}, Output interface: Gi0/0/2
 Preferred path: not configured
 Control Word: enabled, Sequencing: disabled
 FIB Non IP entry: 0x35D6CEEC
 Output chain:  AToM Imp (locks 4) label 22 label [16|44]
  FRR Primary (0x35D10F60)
  <primary:  TAG adj out of GigabitEthernet0/0/2, addr 7.7.7.2 35E88380>
Disposition details:
 Local label: 16
 Control Word: enabled, Sequencing: disabled
 SSS Switch: 3976200193
 Output chain:  mpls_eos( connid router-alert AToM Disp (locks 5)/ drop)

    show mpls infrastructure lfd pseudowire internal

    The following is sample output from the show mpls infrastructure lfd pseudowire internal command:

    Device# show mpls infrastructure lfd pseudowire internal
PW ID: 1VC ID: 4, Nexthop address: 16.16.16.16
SSM Class: SSS HW
Segment Count: 1
VCCV Types Supported:  cw ra ttl
Imposition details:
 Label stack {22 16}, Output interface: Gi0/0/2
 Preferred path: not configured
 Control Word: enabled, Sequencing: disabled
 FIB Non IP entry: 0x35D6CEEC
 Output chain:  AToM Imp (locks 4) label 22 label [16|44]
  FRR Primary (0x35D10F60)
  <primary:  TAG adj out of GigabitEthernet0/0/2, addr 7.7.7.2 35E88380>
Disposition details:
 Local label: 16
 Control Word: enabled, Sequencing: disabled
 SSS Switch: 3976200193
 Output chain:  mpls_eos( connid router-alert AToM Disp (locks 5)/ drop)

    show platform hardware pp active feature cef database

    The following is sample output from the show platform hardware pp active feature cef database command:

    Device# show platform hardware pp active feature cef database ipv4 16.16.16.16/32
=== CEF Prefix ===
16.16.16.16/32 -- next hop: UEA Label OCE (PI:0x104abee0, PD:0x10e6b9c8)
                Route Flags: (0) 
                Handles (PI:0x104ab6e0) (PD:0x10e68140)
 
  HW Info:
    TCAM handle: 0x0000023f    TCAM index: 0x0000000d
    FID index  : 0x0000f804    EAID      : 0x0000808a
    MET        : 0x0000400c    FID Count : 0x00000000

=== Label OCE ===
  Label flags: 4
  Num Labels: 1
  Num Bk Labels: 1
  Out Labels: 16
  Out Backup Labels: 44
  Next OCE Type: Fast ReRoute OCE; Next OCE handle: 0x10e6f428

=== FRR OCE ===
  FRR type         : IP FRR
  FRR state        : Primary
  Primary IF's gid : 3
  Primary FID      : 0x0000f801
  FIFC entries     : 32
  PPO handle       : 0x00000000
  Next OCE         : Adjacency (0x10e63b38)
  Bkup OCE         : Adjacency (0x10e6e590)

=== Adjacency OCE ===
  Adj State: COMPLETE(0)   Address: 7.7.7.2 
  Interface: GigabitEthernet0/0/2   Protocol: TAG 
  mtu:1500, flags:0x0, fixups:0x0, encap_len:14 
  Handles (adj_id:0x00000039) (PI:0x1041d410) (PD:0x10e63b38) 
  Rewrite Str: d0:c2:82:17:8a:82:d0:c2:82:17:f2:02:88:47
 
  HW Info:
    FID index: 0x0000f486    EL3 index: 0x00001003    EL2 index: 0x00000000
    El2RW    : 0x00000107    MET index: 0x0000400c    EAID     : 0x00008060
    HW ADJ FLAGS: 0x40
    Hardware MAC Rewrite Str: d0:c2:82:17:8a:82:08:00:40:00:0d:02

=== Adjacency OCE ===
  Adj State: COMPLETE(0)   Address: 7.7.17.9 
  Interface: GigabitEthernet0/0/7   Protocol: TAG 
  mtu:1500, flags:0x0, fixups:0x0, encap_len:14 
  Handles (adj_id:0x00000012) (PI:0x104acbd0) (PD:0x10e6e590) 
  Rewrite Str: d0:c2:82:17:c9:83:d0:c2:82:17:f2:07:88:47
 
  HW Info:
    FID index: 0x0000f49d    EL3 index: 0x00001008    EL2 index: 0x00000000
    El2RW    : 0x00000111    MET index: 0x00004017    EAID     : 0x0000807d
    HW ADJ FLAGS: 0x40
    Hardware MAC Rewrite Str: d0:c2:82:17:c9:83:08:00:40:00:0d:07

    Additional References

    Related Documents

    Related Topic

    Document Title

    Cisco IOS commands

    Cisco IOS Master Command List, All Releases

    MPLS commands

    Multiprotocol Label Switching Command Reference

    Technical Assistance

    Description

    Link

    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 Loop-Free Alternate Fast Reroute with L2VPN

    The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

    Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

    Table 1 Feature Information for Loop-Free Alternate Fast Reroute with L2VPN

    Feature Name

    Releases

    Feature Information

    Loop-Free Alternate Fast Reroute with L2VPN

    15.3(2)S

    Cisco IOS XE Release 3.9S

    This feature introduces loop-free alternate (LFA) fast reroute (FRR) support for Layer 2 VPN (L2VPN) and Virtual Private Wire Services (VPWS) to minimize packet loss due to link or node failure.

    No commands were introduced or modified.

    In Cisco IOS XE Release 3.9S, support was added for the Cisco ASR 903 Router.