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Setting jumbo protocol MTU in Cisco IOS

IOS has two forms of the "MTU" interface command: one for all protocols and separate explicit commands for each layer-3 protocol, i.e.:

interface pos 0/0
mtu 9000


interface pos 0/0
ip mtu 9000

The first example sets the MTU for all layer-3 protocols, including for example ipv4 and ipv6, to 9000; the second command sets it only for the IP protocol. The first form is generally sufficient. NOTE: not all interfaces and versions of IOS support large MTUs. Check with the Cisco TAC if you're not sure.

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