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Cell Relay Retreat>MPLS-OPS Archive>month:2002-Mar> msg00105



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Tag-switching mtu doubt

  • From: Rui Francisco Negrão Valente <rui.valente@vodafone.pt>
  • Date: Thu, 14 Mar 2002 19:09:28 -0000
  • Resent-Date: Thu, 14 Mar 2002 15:12:07 -0500
  • To: mpls-ops@mplsrc.com

Hi all,

 

Imagine the following VPN scenario:

 

CE----PE---P---P---PE----CE

 

I have FastEthernet in all the links, and tag-switching mtu 1508 at the PEs

and Ps interfaces.

 

Due to the label stacking(2 labels) we have additional 8 bytes in the MTU

size. So, at the CPE the maximum datagram size I can send is 1500 (What I

did was pings with 1500 and with the DF=1).

 

My question is:

 

Why pings fail with datagram size of 1504 from PE to PE?

 From what I understand there will be only one label (4 bytes) pushed in the

packet, therefore the mtu size will be 1508...

 

 

 

Rui Valente

DRE-SE Vodafone(Portugal)

Tel: +351210914085

Mob: +351919513001

rui.valente@vodafone.pt

 


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