[j-nsp] GRE problems

Jonathan Looney jonlooney at gmail.com
Thu Feb 1 10:21:07 EST 2007

If you have enabled PMTUD under the tunnel interface, it seems odd that it
is not working.  Is your network blocking the ICMP fragmentation needed
messages from the upstream router?  However, another option is to manually
lower the MTU under the [edit interfaces gr-x/x/x unit 0 family
(inet|inet6|etc)] hierarchy to account for times when the resilient link is
in use.  You would need to lower it on both ends of the tunnel.  And, this
would be slightly suboptimal in that it would potentially cause
fragmentation of large packets when none is needed; however, at least they
should get through.



On 2/1/07, laura.mcdonnell at canterbury.ac.uk <
laura.mcdonnell at canterbury.ac.uk> wrote:
> I currently use a GRE tunnel to transit traffic from one site to
> another.  However, this tunnel traverses another network which also uses
> a GRE tunnel to transport their traffic over their resilient path.
> I do know when using our GRE tunnel over the providers native primary
> link, there are no problems.  When traffic traverses the resilient link
> (GRE over GRE) large packets do not get through.
> All routers are setup to use PMTUD and given that the routers are using
> the built in tunnel interface I believe setting the TCP MSS value is not
> achievable.
> Does anyone know a work around to this problem?
> Regards,
> Laura McDonnell
> Network Analyst
> Canterbury Christ Church University
> North Holmes Road
> Canterbury
> Kent
> CT1 1QU
> Tel: +44 (0) 1227 782945
> Email: laura.mcdonnell at canterbury.ac.uk
> http://www.canterbury.ac.uk
> http://www.kentman.ac.uk
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> juniper-nsp mailing list juniper-nsp at puck.nether.net
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