Two switches, two trunks

[jcopley01]

Hi all,

I hope this isn't doubling up somewhere.  A few minutes ago I posted a discussion but after clicking the Post Discussion button my post wasn't posted!

I have a site with two switches; a CE520 and a C2960.

The switches have two trunks between them as so:

    one trunk configured with native vlan 100 (voice vlan) on both ends
    one trunk with native vlan 1 on the CE520 port and 100 on the 2960 port - this is generating vlan mismatch erros

I assume whoever set it up perhaps wanted two trunks with two different native vlans.  Only two vlans are used, 1 for the PC network and 100 for our voice (Cisco IP phones).

Is there any benefit to this?  Are two trunks between just two switches totally redundant? Should I match the vlans on the mismatched ports

The network is running fine otherwise.

thanks

Justin

[petenixon]

You should definitely match the native vlan on both ends of the trunk ports, and good practice dictates that the native vlan should be something other than vlan1.

There are reasons for having two separate trunks for vlan traffic and largely depends on your environment. However there is no reason why you couldn't bundle both links into an etherchannel and carry all your vlans across it.

[Joseph W. Doherty]

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Posting

Normally, the only reason to have two different distinct trunk links between switches would be to manage traffic for specific VLANs across each link.  For example, in your case, perhaps the intention was to guarantee one trunk link's bandwidth for VoIP.  This might make sense if one of your switches cannot support QoS.

Another possible reason might be for redundancy, if one of your switches doesn't support Etherchannel.

That said, from what you've described, I think it more likely whoever set up these two trunks wasn't really sure about what they were doing as using VLAN 1 for users is considered a poor practice, generally you don't need to reconfigure native VLANs on trunks, you have the native VLAN mismatch on one trunk, etc.