[c-nsp] Number of MPLS labels and MTU

Piotr Marecki peter at mareccy.org
Sun Feb 5 05:29:49 EST 2006

> Hi,
> Reading Troubleshooting Virtual Private Networks, by Mark Lewis, he states
> that if using VPN MPLS + TE, a label stack depth of three is used  (RSVP
> signaled TE label + TDP/LDP signaled IGP label + VPN label).
> Considering an application generates a packets with higher number of bytes
> (1472) and DF bit set, the packet will have 1514 bytes without label and
> 1514 + 4 + 4 +4 bytes travelling through the network. Do you agree?

I quess you are talking here about entire L2 PDU size on core ethernet  ( 
without 802.1q ) .
If so , 1526 is really minimum that would not be enough if you enable other 
, like 802.1q subinterfaces , FRR , not to mention L2 PWE transport.
> Would it be enough to configure jumbo frame support and mpls mtu under the
> physical interface or it would be necessary any command under the TE
> tunnel interface?

You need only mpls mtu command on your core interfaces ( in this example 
1512 ) , additional
mtu size increase on swicthes ( if any ) . There is no need to increase 
tunnel mtu .


Piotr Marecki

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