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Cell Relay Retreat>MPLS-OPS Archive>month:2001-Oct> msg00173



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Re: Fragmentation in MPLS network BGP problem

  • From: Robert Raszuk <raszuk@cisco.com>
  • Date: Sun, 21 Oct 2001 09:03:56 +0200
  • CC: mpls-ops@mplsrc.com
  • Organization: Signature: http://www.employees.org/~raszuk/sig/
  • Resent-Date: Sun, 21 Oct 2001 04:43:03 -0400
  • To: Marcelo Blanes <mblanes@larc.usp.br>

Marcelo,

> I have PE - P - PE router. If I do a ping in PE to PE if datagram size for
> example 2000 (PE to P router has ether interface if tag mut 1526) with DF
> bit not set, I got I timeout answer. For 1500 it work fine.

You would need to narrows down where your packets are being lost. Maybe
you have a bug of not bumping to process switching (some platforms like
GSR don't support that at all),

> Ok Robert, but iBGP messages ( session VPNv4 ) is exchange between
> loopacks. Will iBGP looks to MTU in the loopback?!

No it does not matter what it the IBGP update-src or dst. It matters via
what PHYSICAL interface the packets are going out of your router, IBGP
is not aware about any MTU issue. It just passed the generated updates
to TCP/IP stack and all fragmentatation is done there.

R.

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