Native Vlan Mismatch

[frenzeus1881]

I have a Cat4506 with a SupII running CatOS 7.6. The 10/100 modules with their ports configured into respective vlans. Trunking has been set to off on the ports. So when i plug in Catalyst 2950 switches, it forms an access link, not a trunk but on the Cat4506 it receives msgs like such:

%CDP-4-NVLANMISMATCH:Native vlan mismatch detected on port 2/11

I only find that the C2950 switches running 12.1(19)EA1c plugged into the Cat4 has the Cat4 producing error msgs of native vlan mismatch. Other C2950 switches running slightly older version is not having the Cat4 producing the errors. I couldn't find any bugs on the IOS version. The configuration of the switches is a simple one, nothing fancy.

 

[bierhunter]

The newer 2950 may be running cdp v2, and the older ones running v1. CDP v2 has more features.

In any case, I've run into the same thing before. It sounds like this is happening.

4506 port is set to a vlan (let's say 5) and configured as an access link.

2950 still set to default out of box (vlan-1).

4506 (vlan-5)<---[access link]--->2950 (vlan-1)

That will technically work and allow traffic to pass, but it will cause the error you are getting. The vlans on each end do not match. It still works, because the 2950 ports are still part of the native vlan.

I would recommend setting up a trunk between switches. Then assign the 2950 ports to the appropriate vlan needed.

4506 (vlan-1)<---[802.1Q trunk]--->2950 (vlan-1) [set individual ports to vlan-5 or whichever is needed].

The benefits aren't always immediately apparent, but this will give you more flexibility and control over your network if you ever have to make changes.

I usually keep a separate subnet for vlan-1 used to managed all my switches. I can then also control who has access to the management subnet.

Example:

vlan-1 (mgt) = 172.16.0.0 /24 (All switches' vlan-1 assigned to this subnet.
Host vlans = 10.x.x.x /xx (subnetted as required for the other vlans)

Only my network guys have access to vlan-1 that way. Just a thought.

BierHunter
CNE, MCSE, CCNP

 

[frenzeus1881]

Thanks for the suggestion. But it would mean a major reconfiguration for the entire network if i were to change to such config. As the thought of having to manage only the distribution and core switches, the 2950 access switches are juz more of a plug and play thing. Will try out the cdp version and see how it goes!

thanks again!