mpls sr ttl-mode

Usage Scenario

TTLs in packets transmitted over SR-MPLS TE and SR-MPLS BE LSPs are processed in either of the following modes:

• Uniform Mode
  The IP TTL value reduces by one each time it passes through a node in an MPLS network.
  When IP packets enter the MPLS network, the ingress reduces the IP TTL value by one and copies the IP TTL value to the MPLS TTL field. Each transit node only processes the MPLS TTL. The egress reduces the MPLS TTL by one, compares the MPLS TTL with the IP TTL, and obtains the smaller value to map it to the IP TTL.
• Pipe Mode
  The IP TTL value decreases by one only when passing through the ingress and egress.
  The ingress reduces the IP TTL value in packets by one and sets the MPLS TTL to a specific value. Transit nodes only process the MPLS TTL. When the egress receives the packets, it removes the MPLS label carrying the MPLS TTL from each packet and reduces the IP TTL value by one.
  When Virtual Circuit Connectivity Verification (VCCV) tracert is used to trace routes of MS-PWs, all nodes on an LSP must use the same TTL processing mode. A mode inconsistency causes a tracert failure.
  When the SR-MPLS TE tunnel is established using the Node label, it is controlled by the command and supports the uniform or pipe modes.
  When the SR-MPLS TE tunnel is established using the Adjacency label, it currently only supports the uniform mode and is not controlled by the command.

Configuration Impact

If the TTL processing mode is changed to pipe on a node of an MPLS network, the tracert and tracert lsp command output does not contain information about this node.