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?
If you increased the MTU for MPLS this will only have an effect within the MPLS network. Once it has left the MPLS network there is no label and so you don't need a larger mtu. So you send a normal ethernet frame of 1500. It gets to the first MPLS router/switch which sets the MTU to 1504, adds a label and switches it to the next MPLS device. This device also has the MTU size set to 1504 so no fragmentation is needed. When the frame is sent from the egress MPLS device to a non-MPLS device there is no label, because the label is only used within the MPLS network and so the frame is 1500 again.
So there is not fragmentation anywhere within the MPLS network.
" if the provider was provided an MPLS VPN wan solution would they change their MTU accordingly"
not quite sure what you are asking here. If a customer purchased an MPLS VPN solution from a provider then the customer would not have to change the MTU on any of their devices because none of the customer links would be running MPLS.
The MTU only becomes important within the provider MPLS network. And as previously stated the MPLS network is under the administrative control of the provider so they could set the MTU wherever they needed to.
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
Introduction Featured Speakers Luis Espejel is the Telecommunications
Manager of IENova, an Oil & Gas company. Currently he works with Cisco
IOS® and Cisco IOS XE platforms, and NX to some extent. He has also
worked as a Senior Engineer with the Routing P...
In this session you can learn more about Layer 3 multicast and the best
practices to identify possible threats and take security measures. It
provides an overview of basic multicast, the best security practices for
use of this technology, and recommendati...