strange switching or routing issue

[netrusoff]

Hi, guys!

I'm experiencing a very strange issue. Let me describe topology first. So we have core switch ( it's a router as well) 4500 stacked via VSS with the another 4500 (ios bootfile is cat4500e-universalk9.SPA.03.09.00.E.152-5) on which nested /23 network let it be 192.168.0.0/23 interface vlan 2, interface vlan3 with network 192.168.50.0/30 is using for connection between core switch and border router. And we have another(remote) network nested on remote router let it be 172.16.0.0/24. So, in  192.168.0.0/23 we have numbers of hosts and we have full access to them from 172.16.0.0/24. But one host, let it be 192.168.0.194, is loosing connectivity in about 10 mins without anyone's attemtps to connect to it from remote network 172.16.0.0/24.For example, i'm trying to ping host 192.168.0.194 from 172.16.0.160 and got timeout response. But if some host from 192.168.0.0/23 gonna ping it, immediatelly i have successfull pings response on 172.16.0.160. I've done monitor capture on core switch, who is a gateway for 192.168.0.0/23 and seen strange things. Packets successfully arriving on interface vlan3 that connected to border router but they don't routed to vlan2   192.168.0.0/23. How it could be possible? vlans 2 and 3 r directly connected. No access-list is used. Help please!

[brselzer · Accepted solution]

Hello,

There is a known issue on 3.9.0 where when we don't learn the mac, we don't flood the packet. I would guess once you ping from another device in the same subnet, you learn the mac again. Can you see if when you start having issue, the mac is not learned?

Can you post the output of the following commands?

show plat hard floodset vlan 2

show plat soft floodset vlan 2

Or whichever vlan the device with the issue is in. Here is the info on the bug:

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvb78700/?referring_site=bugquickviewredir

Unless you have a specific feature you need 3.9.0 for, I would recommend moving to 3.8.5. 3.8.x is our standard maintenance train. 

Hope that helps. Thanks!

[netrusoff]

Thank you very much! Indeed, mac appears right after ping.

I appreciate your help!