[j-nsp] Juniper Ethernet MTU question

[sthaug at nethelp.no]

> Adding a correction based on some actual testing.
> 
> It seems like when mpls mtu is automatically calculated that it subtract
> 12 bytes (for 3 level label stack) from device mtu. Testing shows that
> when you manually configure the mpls family mtu there is no such math,
> so you are actually configuring the mpls *pdu*, which includes data and
> headers.

It would be tremendously helpful if such things could be documented.

We have configured a number of MPLS interfaces with 12 bytes less than
the physical interface MTU - precisely because "show interface" seems to
suggest that is what you *should* configure. I guess we need to change
our configs...

Steinar Haug, Nethelp consulting, sthaug at nethelp.no