OTV Fragmentation

Eduard Gheorghiu · ‎01-29-2016

Hello experts,

The topic is OTV on Nexus 7k peered with ASR1k in unicast mode. I've configured it considering this useful document:

http://www.cisco.com/c/en/us/support/docs/switches/nexus-7000-series-switches/118917-configure-nx7k-00.html

There are however two more requirements:

1. Using multiple join interfaces on ASR 1000. Is it possible?

2. Allowing for fragmentation on WAN. Is it possible on Nexus 7000 F3?

For the first question, in ASR1000 documentation on the Restrictions chapter there is one listed.

Only one join interface can be configured on a router for all overlays.

I've tested on ASR1001-X with two Overlay interfaces using two different join interfaces and it works. It looks like the restriction is not valid maybe because of newer software version or because unicast mode is used.

interface Overlay2

otv join-interface GigabitEthernet0/0/0

interface Overlay3

otv join-interface GigabitEthernet0/0/1

ASR1K#show otv route 

Codes: BD - Bridge-Domain, AD - Admin-Distance,
 SI - Service Instance, * - Backup Route

OTV Unicast MAC Routing Table for Overlay2

 Inst VLAN BD MAC Address AD Owner Next Hops(s)
----------------------------------------------------------
 0 201 201 xxxx.xxcc.8301 40 BD Eng Gi0/0/3:SI201
 0 201 201 xxxx.xx94.8fbf 50 ISIS CORE_A-INTER_DC

2 unicast routes displayed in Overlay2

OTV Unicast MAC Routing Table for Overlay3

 Inst VLAN BD MAC Address AD Owner Next Hops(s)
----------------------------------------------------------
 0 301 301 xxxx.xxcc.8301 40 BD Eng Gi0/0/3:SI301
 0 301 301 xxxx.xx94.8fbf 50 ISIS CORE_A-INTER_DC

2 unicast routes displayed in Overlay3

For the second question, the WAN links cannot provide 1542 bytes MTU so we need to fragment.

There is a similar subject here: https://supportforums.cisco.com/discussion/11396566/otv-asr-1k

On ASR1k the otv fragmentation command is available but I cannot find a similar command for Nexus OS.

Thanks, kinds regards,

Eduard Gheorghiu

Rajeshkumar Gatti · ‎02-02-2016

Answers below-

1. Using multiple join interfaces on ASR 1000. Is it possible?

<Raj>I would follow what is in the config guide. If it is recommended to not use more then 1 join interface then I would stick to it to avoid any future issues. Also if you do run into problem then TAC will definitely indicate that the configured design has unsupported config.

2. Allowing for fragmentation on WAN. Is it possible on Nexus 7000 F3?

<Raj>No. Nexus does not have similar command. Please do not configure it on just one side.

-Raj