What is the relationship between the MTU value of an S12700 interface
and the MPLS MTU value of an interface?
relationship between the MTU value of the interface and the MPLS MTU of the
interface is as follows:
1. If no MPLS MTU value is configured on an interface, the interface MTU is
used to control forwarding of MPLS packets.
2. If both an MPLS MTU value and an interface MTU value are configured on an
interface, the smaller value between the two MTU values is used to control
forwarding of MPLS packets.
informing the upstream device of the LDP MTU, an LSR calculates the LDP MTU by
selecting the smallest value among the MTU values used by all downstream
devices and the MTU of the outbound interface. A downstream LSR uses the preceding
formula to calculate an MTU value, adds it to the MTU TLV in a Label Mapping
message, and sends the Label Mapping message to the upstream device.
MTU value changes (for example, when the local outbound interface or its
configuration changes), an LSR recalculates the MTU value and sends a Label
Mapping message carrying the new MTU value to all upstream devices.