MTU Signaling in RSVP Limitations

The following are limitations to MTU signaling in RSVP:

• Changes in the MTU value might cause a temporary loss of traffic in the following situations:

  • For link protection and node protection, the MTU of the bypass is only signaled at the time the bypass becomes active. During the time it takes for the new path MTU to be propagated, packet loss might occur because of an MTU mismatch.
  • For fast reroute, the MTU of the path is updated only after the detour becomes active, causing a delay in an update to the MTU at the ingress router. Until the MTU is updated, packet loss might occur if there is an MTU mismatch.

    In both cases, only packets that are larger than the detour or bypass MTU are lost.

• When an MTU is updated, it triggers a change in the next hop. Any change in the next hop causes the route statistics to be lost.
• The minimum MTU supported for MTU signaling in RSVP is 1,488 bytes. This value prevents a false or incorrectly configured value from being used.
• For single-hop LSPs, the MTU value displayed by the show commands is the RSVP-signaled value. However, this MPLS value is ignored and the correct IP value is used.