MPLS Point-to-Multipoint Traffic Engineering Support for Static Pseudowires

The MPLS Point-to-Multipoint Traffic Engineering: Support for Static Pseudowires feature transports Layer 2 traffic from a single source to one or more destinations. This feature has the following characteristics:

• It uses L2VPN static PWs to provide point-to-multipoint Layer 2 connectivity over an MPLS network to transport Layer 2 traffic.
• The segmentation for MPLS P2MP TE tunnels provided by this feature allows for applications such as video distribution and clock distribution (mobile backhaul).
• This feature is compatible with Cisco nonstop forwarding (NSF), stateful switchover (SSO). See NSF/SSO--MPLS TE and RSVP Graceful Restart and MPLS Point-to-Multipoint Traffic Engineering for information on configuring NSF/SSO with this feature.
• In this implementation, the PW is bidirectional, in accordance with the Framework and Requirements for Virtual Private Multicast Service .

This feature does not support context-specific label spaces. When configuring the MPLS Point-to-Multipoint Traffic Engineering: Support for Static Pseudowires feature, ensure that local bindings are unique. Otherwise, traffic unintentionally merges. In the figure below, both PWs share router PE 3 as an endpoint. The local label on each PW is 16, which causes a collision.

Figure 1

Avoiding VC Label Collisions

For P2MP static PWs, there is no signaling protocol to verify that the labels are configured correctly on either end. If the labels are not configured correctly, traffic might go to the wrong destinations. Because the traffic going into wrong destinations is a multicast confutation, scalability might be impacted.

The P2MP static PW does not have a context-specific label in the upstream direction and does not use a signaling protocol. Therefore, it is possible to spoof a PW label and route the traffic to the wrong destination. If a PW label is spoofed at the headend, it cannot be validated at the tailend, because the MPLS lookup at the tailend is performed on the global table. So if a spoofed label exists in the global table, traffic is routed to the wrong destination: customer equipment (CE).

The same situation can happen if the user incorrectly configures the static PW label. If the wrong PW label is configured, traffic goes to the wrong destination (CE).

The figure below shows PW label allocation with no context-specific label space.

Figure 2

PW Label Allocation with No Context-Specific Label Space

1.    enable

2.    configure terminal

3.    pseudowire-class class-name

4.    encapsulation mpls

5.    protocol none

6.    preferred-path [interfacetunneltunnel-number][disable-fallback]

7.    exit

8.    interface tunnel number

9.    ip unnumbered loopback number

10.    tunnel mode mpls traffic-eng point-to-multipoint

11.    tunnel destination list mpls traffic-eng {identifierdest-list-id | namedest-list-name}

12.    exit

13.    interface loopback number

14.    ip address [ip-addressmask [secondary]]

15.    exit

16.    interface ethernet number

17.    no ip address [ip-addressmask [secondary]]

18.    no keepalive [period [retries]]

19.    xconnect peer-ip-address vcid encapsulation mpls manual pw-class class-name

20.    mpls label local-pseudowire-label remote-pseudowire-label

21.    mpls control-word

22.    end

1.    enable

2.    configure terminal

3.    pseudowire-class class-name

4.    encapsulation mpls

5.    protocol none

6.    exit

7.    interface loopback number

8.    ip address [ip-addressmask [secondary]]

9.    exit

10.    interface ethernet number

11.    no ip address [ip-addressmask [secondary]]

12.    no keepalive [period [retries]]

13.    xconnect peer-ip-address vcid encapsulation mpls manual pw-class class-name

14.    mpls label local-pseudowire-label remote-pseudowire-label

15.    mpls control-word

16.    end

1.    show mpls l2transport vc detail

2.    ping mpls pseudowire ipv4-address vc-id vc-id

Router# show mpls l2transport vc detail
Local interface: Et1/0 up, line protocol up, Ethernet up
  Destination address: 10.0.1.1, VC ID: 200, VC status: up
    Output interface: Et3/0, imposed label stack {17}
    Preferred path: not configured  
    Default path:
    Next hop: 10.0.0.2
  Create time: 00:27:27, last status change time: 00:27:24
  Signaling protocol: Manual
    MPLS VC labels: local 17, remote 17 
    Group ID: local 0, remote 0
    MTU: local 1500, remote 1500
  Sequencing: receive disabled, send disabled
  VC statistics:
    packet totals: receive 193, send 193
    byte totals:   receive 19728, send 23554
    packet drops:  receive 0, send 0

Router# ping mpls pseudowire 10.7.1.2 vc-id 1001
Sending 5, 100-byte MPLS Echos to 10.7.1.2,
      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 label entry,
   '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 = 1/2/4 ms