I am currently studying for the ISCW exam and have a question regarding MTU. When studying GRE or IPsec tunnels the MTU size can be reduced to support links that do no support the additional overhead of the encapsulation through out the topology. This made perfect sense to me so things don't have to be fragmented and retransmitted.
Then I started reading the MPLS chapter and it stated with the additional overhead of the MPLS frame you could increase the mpls mtu size. So for example on an ethernet link it could go from 1500 to 1504.
Why would it be increased if there could be potential fragmentation and MTU issues with other links in the topology?