I will give some examples of changing MTU on Juniper MX.
The MTU range can be specified from 256 to 9500 bytes for the MX series.
An example of changing the MTU on an aggregated interface (no need to change on child interfaces):
set interfaces ae0 mtu 9000
An example of a change on the physical interface:
set interfaces et-0/0/2 mtu 9000
Change MTU for vlan 100:
set interfaces et-0/0/2 unit 100 family inet mtu 1500
Apply changes:
commit check
commit
Let’s check the changes:
run show interfaces ae0 extensive
run show interfaces et-0/0/2 extensive
run show interfaces et-0/0/2.100 extensive
See also my article:
Juniper MX204 setup