[j-nsp] MTU issues.

sthaug at nethelp.no sthaug at nethelp.no
Tue Mar 17 10:23:08 EDT 2009

> Nilesh is right  I think , in juniper you specify only payload size ,
> in cisco you specify full frame size (ip header+icmp header+Payload)

If you specify the MTU on the physical interface it definitely 
includes L2 overhead. For example, this is a GigE link with 4470

ge-0/2/0 {
    mtu 4484;
    unit 0 {
        family inet {
            address a.b.c.d/30;
        family iso;
        family mpls;

And "show interfaces" shows the IP etc MTU. Extract:

sthaug at cr1.osls> show interfaces ge-0/2/0
Physical interface: ge-0/2/0, Enabled, Physical link is Up
  Logical interface ge-0/2/0.0 (Index 77) (SNMP ifIndex 300)
    Protocol inet, MTU: 4470
    Protocol iso, MTU: 4467
    Protocol inet6, MTU: 4470
    Protocol mpls, MTU: 4458

Steinar Haug, Nethelp consulting, sthaug at nethelp.no

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