[c-nsp] MPLS VPN over mGRE - PMTUD?

[Alasdair McWilliam]

Thanks for the heads up on that.

My 'PE' routers will be 7200-NPE400 FE in/out or ASR1k GbE in/out (and possibly ISR 3945s if/when the feature is available..) all with standard 1500MTU. Inside LAN interfaces will be subinterfaces (one per VRF) and outside WAN interfaces will be access ports running IGP into IP core. Providing I can ensure ICMP Unreachables through the client/server end to end path, I guess I should be OK. Would you recommend setting anything like mss adjust on the inside sub-interfaces if I can't? (Or as well as?!)

Do you (or anyone...) think there would be any noticeable performance penalty (latency, throughput) with this scenario?

I have not yet investigated the possibility of simply increasing the MTU on all my outside core interfaces but that is most likely out of my control!

Any help/comments/suggestions appreciated! :-)

Cheers
Al


On 29 Sep 2010, at 21:40, Benjamin Lovell wrote:

> If you are looking to do this for setting the MPLS MTU dynamically then I don't think this will help as starting with our forwarding infrastructure rewrite in 12.4(20)T (I would need to check to be sure when/if in other code trains) we lost the ability to set the MPLS MTU on tunnel interfaces. 
> 
> See CSCth11646.
> 
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>           .            .          Benjamin Lovell
>           |            |          AS Video Practice
>          |||          |||         Cisco Customer Advocacy
>        .|||||.      .|||||.       Research Triangle Park, NC
>     .:|||||||||:..:|||||||||:.    Email:  belovell at cisco.com
>              cisco            desk:919.392.8255 cell:203.509.1562
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> On Sep 29, 2010, at 3:17 PM, Alasdair McWilliam wrote:
> 
>> Hi List,
>> 
>> Apologies if this is hidden in the list somewhere, but I've done a bit of Googling and can't find too much.. so here goes!
>> 
>> I'm looking at implementing an MPLS VPN over mGRE solution to facilitate routing instance segregation across multiple, geographically separate sites, across a third party Layer 3 infrastructure. (12.2SRE for 7200, IOS-XE 3 for ASR1k and looks to be coming into ISR G2 in 15.1T.) However given the mix of GRE encapsulation to provide the PE-PE connectivity, I'm a bit worried that apps might have a hissy fit.
>> 
>> My question is, does anyone know if it's possible to enable PMTUD with this feature? I've got it setup in a lab and the Tunnel0 and Tunnel1 interfaces cannot be directly modified from the CLI (they don't appear in config either...)
>> 
>> The next best thing I can see would be Dynamic L3 VPNs over mGRE, but that isn't available on the platforms I use, and I really don't want to go as far as to enable full blown MPLS over point to point GRE tunnels if I can at all avoid it!
>> 
>> Any tips? :-)
>> 
>> Cheers
>> Al
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