MTU problem in MPLS cloud

[eecwkac]

PE1-P1-P2-P3-P4-PE2

if we know that the MTU in one of the backbone link srunning mpls is smaller than of ther others. then we want to check the MTU workable on this MPLS cloud,then we ping from PE1 with different packet size and DF set to PE2, then should we increase the packet size until we cannot ping to PE2, or at the very begining, we should use largest packet size and then decrease the packet size until we find out the suitable MTU?

[sbilgi]

The procedure for calculating the MTU sizing in MPLS network is the same as any normal Ip network.

The following document will help you: http://www.cisco.com/warp/public/105/38.shtml

We should use a larger MTU for the packet to see if it exceeds the MTU on the intermediate links. IfICMP error is received, we have to reduce the MTU and see at what size the ICMP error is not reported.