This section provides an overview of the association signaling methods for the bidirectional LSPs. Two unidirectional LSPs can be bound to form an associated bidirectional LSP in the following scenarios:

• No unidirectional LSP exists, and both must be established.

• Both unidirectional LSPs exist, but the association must be established.

• One unidirectional LSP exists, but the reverse associated LSP must be established.

This section provides an overview of associated bidirectional co-routed LSPs. Establishment of MPLS TE-LSP involves computation of a path between a head-end node to a tail-end node, signaling along the path, and modification of intermediate nodes along the path. The signaling process ensures bandwidth reservation (if signaled bandwidth is lesser than 0 and programming of forwarding entries).

Path computation is performed by the head-end nodes of both the participating LSPs using Constrained Shortest Path First (CSPF). CSPF is the 'shortest path (measured in terms of cost) that satisfies all relevant LSP TE constraints or attributes, such as required bandwidth, priority and so on.

Associated Bidirectional Co-routed LSPs: A co-routed bidirectional TE LSP denotes a bidirectional tunnel where the forward direction LSP and reverse direction LSP must follow the same path, for example, the same nodes and paths. Here is an illustration.

In the above topology:

• Paths at the top of the figure (in green) indicate working co-routed LSP pairs.

• Paths at the bottom of the figure (in red) indicate protecting co-routed LSP pairs.

• Router 1 sets up working LSP to Router 3 (in green) after performing bidirectional CSPF and sends reverse explicit route object (ERO) to Router 3. Node Router 3 uses the received reverse ERO to set up reverse green working LSP to Router 1.

• Router 3 sets up protecting LSP to Router 1 (in red) after performing bidirectional CSPF and sends reverse ERO to Router 1. Node Router 1 uses the received reverse ERO to set up reverse red protecting LSP to Router 3.

• Exp-null over Flex-LSP is not supported.

• 50 msec convergence is not guaranteed without WRAP protection. WRAP protection is mandatory to achieve 50 msec convergence for remote failures.

• TE NSR and IGP NSR are mandatory for RSP switchover.

• VPLS over Flex-LSP is not supported.

• Non-co routed Flex LSP is not supported.

• Sub interface shut will not guarantee 50 msec convergence.

• MPLS forwarding table stats is not supported.

• 1000 tunnels are supported with wrap protection and path protection.

Following list outlines key features supported:

• Protection -

  Following Protection features are supported:

  • Lockout: Using Lockout feature, user can perform lockout protection on a selected LSP and can switch traffic to protecting LSP, if the selected LSP carries the traffic. LSP on locked out interface remains up but no traffic flows on the locked out path. To configure lockout under an MPLS-TE enabled interface:

    
    RP/0/RP0/CPU0:router# configure
    RP/0/RP0/CPU0:router(config)# mpls traffic-eng
    RP/0/RP0/CPU0:router(config-mpls-te)# interface tenGigE0/1/0/1
    RP/0/RP0/CPU0:router(config-mpls-te-if)# fault-oam lockout

  • Wrap Protection: Using Wrap Protection, each LSP signals unique wrap label for head-end to identify lookback traffic and sends it over protect LSP. To configure Wrap Protection:

    
    RP/0/RP0/CPU0:router# configure
    RP/0/RP0/CPU0:router(config)# interface tunnel-te1
    RP/0/RP0/CPU0:router(config-if)# ipv4 unnumbered Loopback0
    RP/0/RP0/CPU0:router(config-if)# destination 49.49.49.2
    RP/0/RP0/CPU0:router(config-if)# path-option 10 explicit name PATH1-2-3 
    RP/0/RP0/CPU0:router(config-if)# bidirectional association id 100 source-address 49.49.49.2
    RP/0/RP0/CPU0:router(config-if)# bidirectional association association type co-routed
    RP/0/RP0/CPU0:router(config-if)# wrap-protection
    RP/0/RP0/CPU0:router(config-if)# fault-oam 
    

• MPLS-OAM: MPLS-OAM supports single segment pseudowire going over the associated bidirectional TE tunnels. This support includes pseudowires signaled dynamically, statically, or using a mix of both modes. To configure MPLS-OAM, use the following command:

  
  RP/0/RP0/CPU0:router# configure
  RP/0/RP0/CPU0:router(config)# mpls oam
  RP/0/RP0/CPU0:router(config-oam)# echo reply-mode control-channel allow-reverse-lsp
  

  Following features are supported:

  • LSP Ping: Using LSP ping, use can enable on demand ping. It supports IP encapsulation for both request and reply messages. It also performs reverse path verification.

    Following is the example of LSP Ping configuration:

    
    RP/0/RP0/CPU0:router# ping mpls traffic-eng tunnel-te 1 reply mode control-channel
    
    Tue May 21 11:04:12.211 EDT
    Sending 5, 100-byte MPLS Echos to tunnel-te1,
          timeout is 2 seconds, send interval is 0 msec:
    
    Codes: '!' - success, 'Q' - request not sent, '.' - timeout,
      'L' - labeled output interface, 'B' - unlabeled output interface,
      'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,
      'M' - malformed request, 'm' - unsupported tlvs, 'N' - no rx label,
      'P' - no rx intf label prot, 'p' - premature termination of LSP,
      'R' - transit router, 'I' - unknown upstream index,
      'X' - unknown return code, 'x' - return code 0
    
    Type escape sequence to abort.
    
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 3/4/5 ms

  • Traceroute: Traceroute supports IP-encapsulation but not for echo reply. Following is the example of Traceroute configuration:

    
    RP/0/RP0/CPU0:router# traceroute mpls traffic-eng tunnel-te 1
    
    Tue May 21 11:06:16.056 EDT
    Tracing MPLS TE Label Switched Path on tunnel-te1, timeout is 2 seconds
    
    Codes: '!' - success, 'Q' - request not sent, '.' - timeout,
      'L' - labeled output interface, 'B' - unlabeled output interface,
      'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,
      'M' - malformed request, 'm' - unsupported tlvs, 'N' - no rx label,
      'P' - no rx intf label prot, 'p' - premature termination of LSP,
      'R' - transit router, 'I' - unknown upstream index,
      'X' - unknown return code, 'x' - return code 0
    
    Type escape sequence to abort.
    
      0 10.10.10.1 MRU 1500 [Labels: 16005 Exp: 0]
    L 1 10.10.10.2 MRU 1500 [Labels: implicit-null Exp: 0] 11 ms
    ! 2 13.13.13.4 4 ms
    

Scale details for Flex LSP:

A co-routed bidirectional packet LSP is a combination of two LSPs (one in the forward direction and the other in reverse direction) sharing the same path between a pair of ingress and egress nodes. It is established using the extensions to RSVP-TE. This type of LSP can be used to carry any of the standard types of MPLS-based traffic, including Layer 2 VPNs.

The configuration includes the following steps:

1. Enable basic MPLS Traffic Engineering on hostname PE1 and RSVP Configuration.

2. Configure Flex LSP.

3. Enable Wrap Protection.

4. Enable Fault OAM.

5. Map pseudowire to a specific Flex LSP tunnel.