[c-nsp] MTU packet loss problem 12410 XR and 6509

[Gustav UHLANDER]

Hello.

In ios-xr the mtu is the L2 mtu while in vanilla ios the mtu is L3 mtu. 
This gives that XR is including L2 headers in the mtu setting. So in reality you have matching MTUs at present but when you configure XR with an mtu of 1500 you get a mismatch. 
How is the etherchannel configured? Is the 6509 routing anything or are you using it as a switch? 

Bästa hälsningar / Best regards,

Gustav Uhlander
Senior Communication & Infrastructure Engineer

Steria AB
Kungsbron 13
Box 169
SE-101 23  Stockholm
Sweden

Tel: +46 8 622 42 15
Fax: +46 8 622 42 23
Mobile: +46 70 962 71 03
gustav.ulander at steria.se 
www.steria.se

-----Original Message-----
From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Lee Starnes
Sent: den 20 maj 2014 23:00
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] MTU packet loss problem 12410 XR and 6509

Hello everyone,

A strange MTU issue has popped up and for the life of me I am unable to figure out why. This seems to only affect one Metro-E carrier and only when the traffic passes between the 6500 and the 12410.

ME Carrier A ---> 10G 6509 ----bundle-ether1(4G)--->12410A
ME Carrier B ---/                 \-----bundle-ether2(4G)--->12410B
ME Carrier C --/

Traffic that passes from either 12410 to customer links on ME carrier A are seeing MTU issues and packet loss. Traffic across those same links for carriers B and C have no issue. To test this, we can ping from from the
12410 to a site on ME carrier A with 1500byte packet size and get packet loss. The same test to clients on ME carrier B and C have no issues. Now, since no changes were made on our end and the carrier states no changes were made on their end, we are at a standstill.

However, I did see that the MTU size on the 12410's is by default 1514 and the MTU on the 6500 is 1500. Changing this to match 1500 on both sides causes no traffic to pass. I'm not sure why both sides of the bundle-ether interfaces matching MTU causes 100% packet loss.

Anybody have any ideas on why matching MTU size would cause no traffic to pass? Ultimately the carrier will need to fix their issue, but I would like to understand why this problem of matched MTU sizes causes no traffic.

Thanks.

-Lee
_______________________________________________
cisco-nsp mailing list  cisco-nsp at puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/

-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2014.0.4570 / Virus Database: 3950/7522 - Release Date: 05/19/14