[c-nsp] Multiple 802.1q subinterfaces with the same vlan underthesame physical interface

[Oliver Boehmer (oboehmer)]

luismi <mailto:asturluismi at gmail.com> wrote on Wednesday, July 02, 2008 11:23 AM:

> What I was thinking in assign different subinterfaces (from different
> physical interfaces) to the same vlan in the same chassis.
> 
> I think that the router will be able to manage that configuration, for
> example: fa0/0.1 and fa1/0.1 working in different vrfs but in the same
> vlan, with different IP address from the same subnet.
> 
> Is that correct?

yes, this will work on most platforms. The 6500/7600 uses system-wide vlans (with a few exceptions), so this won't work there..
Tom's comment on the (possibly connected) switched infrastructure still applies, but if you are "only" consolidating the router part, it should work.

	oli


> 
> El mié, 02-07-2008 a las 08:22 +0200, Oliver Boehmer (oboehmer)
> escribió:
>> luismi <> wrote on Monday, June 30, 2008 8:15 PM:
>> 
>>> Hi there,
>>> 
>>> I have a dude I could solve using a lab enviroment but for several
>>> reasons I don't have enought time at this momment, neither I have
>>> the correct equipment here. 
>>> 
>>> I am thinking on collapse several routers configurations in new
>>> equipment, deploying subinterfaces with 802.1q and VRFs.
>>> 
>>> The situation is that for the same physical interface I would have
>>> several subinterfaces, working in the same vlan but diferent vrf,
>>> with also diferent ip addresses but all of them are in the same
>>> subnet. 
>>> 
>>> The question is, is the router going to be enough clever to deliver
>>> the packet in the correct interface? Take note that the IP address
>>> use as destination in the incoming packet is not going to be ip
>>> address of the interface since the router and its vrfs.
>> 
>> This is not going to work. The router needs the vlan tag to associate
>> the appropriate (sub)interface with the packet, so the vlan tag has
>> to be unique on the interface (some platforms like the 6500 even ask
>> for a unique tag per system). VRF association comes later and is
>> based on the vrf configured on the (sub)interface.
>> So if you want to consolidate multiple vlan/.1q connections, you will
>> need to change vlan IDs in order to make them unique.
>> 
>> 	oli