Ok in case I have some eoip tunnel or MPLS/VPLS interface and some vlan I have to modify only the L2mtu without change MTU, because are all protocol that use L2 stack..exactly?
In what case is necessary to increase MTU??Can you ask me an example?
Here is a presentation that deals with MTU when using MPLS/VPLS: http://tiktube.com/video/KHhE3aEKdDoDEJ ... sDlIoFqoq=
After watching that, if you still have any questions, ask.
As for increasing MTU, it is only usefull when you need to route packets larger then 1500 on L3. Meaning, if you need to route jumbo packets.
Usually, jumbos do not leave the L2 segment, meaning communication between 2 hosts with jumbos is usually direct host-to-host traffic, without being routed.
There is nothing preventing you from routing jumbos if you need it tho. As mentioned, watch out for MTU issues over longer routed paths, and make sure PMTUD works, or use other work-arounds, such as changing MSS.
I have not yet seen a network that routes jumbos, but there are valid reasons and scenarios to do so.
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