1921 VLAN

[JayNEC]

I want to have a 1921 router with an HWIC-1FE, and have routing and VLAN's. Do I just do this with a subinterface and encapsulation?
I'll end up with a pair of 1921 routers with a route between them over an ethernet pipe, and I need to trunk a vlan across that same pipe. Actually two ethernet pipes - one redundant, and I need to carry the VLAN across both.

That's the reason for the HWIC - there's two WAN links that are presented as ethernet, and one LAN port so I need the three ethernet interfaces.

The two WAN links will either be load-balance or failover, not sure which yet.

 

[baddos]

Why do you want to trunk your vlans across your wan?

 

[unclerico]

Are you sure that the circuit is Ethernet end-to-end or is it just an Ethernet handoff?? If it is something along the lines of Switched Ethernet/NLAN/<insert provider Ethernet offering here> then, yes, you would create subinterfaces on the router. As baddos says, why are you doing it this way though?? While you'll successfully configure dot1q encapsulated subinterfaces between the two 1921's, you will still have different network ranges on each side of the 1921's unless you configure IRB or implement tunnels. A better option would be to place a switch on each side of the link and create trunks on there, that way you can extend your VLANs between sites. Also, your physical design is more aligned with load-balancing than failover as your 1921's still present single points of failure.

 

[JayNEC]

This network is already in existence. It's a wireless radio shot which is just layer 2. Currently there is a router (Adtran) on only one end of the wireless and it owns an IP in both subnets. Obviously this sucks.

There is a specific application that needs to be trunked across a VLAN (separate IP subnet from the rest of the network but it spans the VLAN and is outside my control). The wireless shot is currently carrying the VLAN successfully.

I'm putting in the pair of routers to get the L2 traffic off the wireless as well as to provide failover to a ethernet WAN link that's being added for redundancy (I'm assured it can carry the VLAN tagging as well). I just want the VLAN pass a specific set of devices traffic as L2 (very limited) and the rest will be L3 on the regular vlan.

So, the ethernet interface would be configured as normal between the two routers, then I can create a subinterface and assign a vlan tag to it? I don't beleive I need a special IOS version - AFAIK you used to need IP Plus.

 

[VinceWhirlwind]

I can understand the need to trunk VLANs across a WAN link - people need this for VMotion, for example, where they have a cluster of VMWare servers with half of them on a DR site. I'm sure other clustered applications are similar. Storage and backups, for example.

The new WAN link either supports Layer2 or doesn't.
- If it does, then you don't need routers for the link itself. You obviously need a router on each site for you inter-VLAN routing.
- If it doesn't, then you can't trunk a VLAN across it without doing some sort of horrible tunnel.

 

[JayNEC]

I definitely want routers on each side of a WAN link. I don't want to treat a skinny WAN pipe like a L2 link and allow those broadcasts across there.

 

[VinceWhirlwind]

Like any good network design, you should avoid trunking VLANs across links they're not needed on. You only need one subnet to exist in both places, the rest of the VLANs you trunk across should be point-to-point subnets only.
But I don't think we've established your WAN link supports L2 end-to-end yet?

 

[JayNEC]

Yes, it does. the existing one does (and is carrying a VLAN) and the additional new one the provider assures us it will carry a VLAN tag as well.

I agree with the fact that carrying a VLAN trunk across the WAN is not good, but it's needed in this case and it's a very limited number of devices that exist in this VLAN (only 3 devices), and they are not broadcast chatty PC's.

 

[VinceWhirlwind]

So on the two routers that face each other across the new WAN link, you create two subinterfaces - one each for VLANs 10 & 20.

VLAN 10 is a point-to-point subnet linking the two routers across the WAN.
VLAN 20 is then trunked out the "inside" of each router into the internal LAN to be your Layer2 subnet that spans both sites.

 

[unclerico]

Just to make sure, you are terminating the Ethernet handoff on switches that support dot1q??

 

[JayNEC]

I am terminating the Ethernet handoff directly on the routers Ethernet port