[j-nsp] Path MTU Discovery - MPLS VPN

masood at nexlinx.net.pk masood at nexlinx.net.pk
Wed May 27 11:46:01 EDT 2009

the vrf IP address is drawn from among the IP addresses associated with
interfaces configured for that routing instance. so you meet that

to enable path checks on the outgoing interface for unicast traffic routed
on a VRF routing instance, you may need to include the vrf-mtu-check
statement under chassis.

[edit chassis]

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

> 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.
> Cheers,
> Tim.
> -----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
> Cc:
> 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.
> BR//
> Masood
> 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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