[c-nsp] Secondary IP address causing MTU reduction?

Eric A Louie elouie at yahoo.com
Wed Dec 17 05:58:18 EST 2014

ME-3600X Version 15.2(4)S, RELEASE SOFTWARE (fc1)ASR1001 Version 15.3(1)S1, RELEASE SOFTWARE (fc1)
ME-3600X G0/1 is connected to ASR 1001 G0/0/1
ME-3600Xinterface GigabitEthernet0/1
 description uplink-nav-oxr-core1
 switchport access vlan 100
 mtu 9200
interface Vlan100
 description nav-oxr-base1-mgmt
 mtu 9200
 ip address XXX.209.96.102
 ip ospf cost 10

ASR 1001interface GigabitEthernet0/0/1
 description uplink-nav-oxr-base1
 mtu 9200
 ip address XXX.209.96.97
 ip flow ingress
 ip flow egress
 ip ospf cost 10
 negotiation auto
 mpls ip
 cdp enable


     On Tuesday, December 16, 2014 6:28 PM, David Coulson <david at davidcoulson.net> wrote:

 What platform? What code?

Can you post your interface config?

Sent from my iPhone

> On Dec 16, 2014, at 9:22 PM, Eric A Louie via cisco-nsp <cisco-nsp at puck.nether.net> wrote:
> I encountered a strange problem that I'm hoping is a bug.
> Directly connected routersMTU 9200Works fine with single IP addresses
> As soon as I put a secondary address on both interfaces (one VLAN, one physical interface), the MTU allowed magically decreased to 1477.  1500 byte packets with DF set would not pass.
> Removing the secondaries fixed the problem.
> Anyone seen this before?
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