Re-using same vlan number at different distribution blocks

[Madura Malwatte]

Just wanted to know what is the best practice in terms of reusing vlan numbers in different distribution blocks in a 3 tier network. ie layer 2 from access to distribution and layer 3 between distributions and core.

access--L2---distribution1---L3---core---L3---distribution2---L2--access

Is it best practice to use the same vlan numbers (obviously they will have a different ip subnet) in each of the 2 distribution blocks? Say distribution1: vlan 10 mgmt & vlan 20 data and distribution2: vlan 10 mgmt & vlan 20 data. 

[Seb Rupik]

Hi there,

If it brings uniformity to your network topology then it can only be a good thing. I certainly have employed the same practice at remote sites, but safe in the knowledge that these Layer2 segements will never meet.

Doing the same, from what you describe on a campus network is slightly more risky. So long as the existing core-distribution L3 links never start carrying these shared VLAN IDs your design will be fine. I assume you have used routed interfaces to try and mitigate accidental trunking?

cheers,

Seb.

[Philip D'Ath]

I'd do it for remote sites where their layer 2 can never meet, but not in a campus in case a misconfiguration occurs and you end up bridging between them instead of routing.

[Joseph W. Doherty]

As the others have noted, across remote sites where there's almost no chance you'll ever mix such numbered VLANs, reusing the VLAN numbers, for the same purpose, probably makes the most sense.

For same site network, where you may need to mix VLANs on the same device, yet you don't want them to be the same VLAN, you'll want to keep the series different. In these cases, you might be able to use part of the VLAN number for the "group" and part of the VLAN number of the function. E.g. (11, 12, 13), (21, 22, 23) or (11, 21, 31), (12, 22, 32) etc.