[j-nsp] Path MTU Discovery - MPLS VPN

tim.hunt at bt.com tim.hunt at bt.com
Wed May 27 10:31:03 EDT 2009

Thanks Masood, I have an FE associated with the VRF on the CE/PE router
with a /26 assigned and so I assume I meet that requirement?

Should path MTU check work within the MPLS cloud ie. Say a link from the
P to PE has a reduced MTU? IS there any general info out there that
would help? I had a look at the RFC.


-----Original Message-----
From: masood at nexlinx.net.pk [mailto:masood at nexlinx.net.pk] 
Sent: 27 May 2009 16:28
To: Hunt,TJ,Tim,DMH2 R
Subject: Re: [j-nsp] Path MTU Discovery - MPLS VPN

path mtu check requires at least one IP address must be associated with
each vrf. If an IP address is not associated with the routing instance,
icmp reply messages cannot be sent.

Blog: http://weblogs.com.pk/jahil/

> Hi,
> I've been trying to  get Path MTU Discovery working for M/J-series, 
> appreciate that the M-series requires vrf-mtu-check <id-10380545.html>

> setting. Having done this I've tried testing it by launching Pings (DF
> set) with a larger MTU than the link, but I'm getting no response at 
> all
> - expecting ICMP response.
> Has anyone any experience of the above? What stops it from working? - 
> I have vrf-table-label set on some CE/PE devices. Is my test valid?
> Thanks,
> Tim.
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