Linktrace

A linktrace message is originated by an MEP and targeted to a peer MEP in the same MA and within the same MD level (see Figure: CFM linktrace). Its function is similar to IP traceroute. Linktrace traces a specific MAC address through the service. The peer MEP responds with a linktrace reply message after successful inspection of the linktrace message. The MIPs along the path also process the linktrace message and respond with linktrace replies to the originating MEP if the received linktrace message that has a TTL greater than 1; the MIPs also forward the linktrace message if a lookup of the target MAC address in the Layer 2 FIB is successful. The originating MEP will receive multiple linktrace replies and from processing the linktrace replies, it can put together the route to the target bridge.

A traced MAC address (the targeted MAC address) is carried in the payload of the linktrace message. Each MIP and MEP receiving the linktrace message checks whether it has learned the target MAC address. To use linktrace, the target MAC address must have been learned by the nodes in the network. If the address has been learned, a linktrace message is sent back to the originating MEP. A MIP forwards the linktrace message out of the port where the target MAC address was learned.

The linktrace message has a multicast destination address. On a broadcast LAN, it can be received by multiple nodes connected to that LAN; However, only one node will send a reply.

Figure: CFM linktrace

The following linktrace-related functions are supported:

• Linktrace functions can be enabled or disabled on an MEP.

• A MEP supports generating linktrace messages and responding with linktrace reply messages.

• A MIP supports responding to linktrace messages with linktrace reply messages when encoded TTL is greater than 1; The MIPs forward the linktrace messages accordingly if a lookup of the target MAC address in the Layer 2 FIB is successful.

• The Sender ID TLV may optionally be configured to carry the Chassis ID. When configured, the following information will be included in LTM and LTR messages:

  • Only the Chassis ID portion of the TLV will be included.

  • The Management Domain and Management Address fields are not supported on transmission.

  • The LBM message will include the Sender ID TLV that is configured on the launch point. The LBR message will include the Sender ID TLV information from the reflector (MIP or MEP) if it is supported.

  • The Sender ID TLV is supported for service (id-permission) MEPs.

  • The Sender ID TLV is supported for both MEPs and MIPs.

The display output has been updated to include the Sender ID TLV contents if they are included in the LBR.

oam eth-cfm linktrace 00:00:00:00:00:30 mep 28 domain 14 association 2
Index Ingress Mac          Egress Mac           Relay     Action
----- -------------------- -------------------- ---------- ----------
1     00:00:00:00:00:00    00:00:00:00:00:30    n/a       terminate
SenderId TLV: ChassisId (local)
              access-012-west
----- -------------------- -------------------- ---------- ----------
No more responses received in the last 6 seconds.