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New Member

vlan id in ospf AS


I just want to confirm something regarding the VLAN ID

Our customer is having an AS with some about 20 OSPF areas. I am now providing a CORE switch on 1 of this areas with a VLAN implementation on it.

The AS admin was saying;

1.He will only provide me with VLAN ID whom i could use. His idea was VLAN ID which is already used, say in the AREA 0 core couldnt be used in any of the areas, siting there will be a vlan mismatch.

2. The number of VLANS is Autinomous System significant telling the whole AS is limited to 1024 VLANS.

My comment;

1. vlan is layer 2 and is only locally significant and therefore not going to propagate throughout the ospf AS. So i could use any vlan id i want..and i dont care what vlan ids other areas have used.

2. Number of maximum vlans is again locally significant and is only dependent on the switch (not taking into account the number of vlans created by the other areas on the said AS).

Can I have your views on this. Because I wanted to get back to them as to what is the right idea.

Thanks a lot.

New Member

Re: vlan id in ospf AS


For point 1. I agree. The VLAN ID is only carried in an 802.1Q header, so if there is no 802.1Q between two switches, then they can use the same VLAN ID with no conflict. CDP reports native VLAN mismatches, but again this is between two switches running 802.1Q directly.

For point 2, I agree. I think current software supports 4096 VLANs.

Re: vlan id in ospf AS

From technical viewpoint you're of course right. But they may have administrative concerns. For ease of maintanence/troubleshooting etc. they may have preferred to use AS-wide unique vlan ids.


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