how to get layer 2 trough layer 3 ?

You could use tunneling with GRE and bridging (not very smart solution) or you could use one of the available methods like L2TP or AoMPLS, depends on your use and if it it just one rotuer or a number of them.

hi Ivan,

thank you for your help, its still all about my problem mentioned in the "Fallback bedween a Laserlink and a HDSL modem line" post.

ok, could you give me some hints where to start wenn i dlike to push dot1q traffic with your suggestions through this here

i think i have put a router there where my switches currently are, connect it to the laser /modem and then connect each router to my building switch. i'm still not getting this right.

how about taking two cat 3550 and use 802.1q tunneling on these tho

3550-SMIs in the middle witch are directly attached to the laser and the modem. As decribed here Updated version: the dot1q trunkport on the"edge" switches. then i just need a to give the two 3550er in the middle for each line a own vlan and a management ip. now via this management ips i could base my routing of that tunneling port. and like this i could make sure the traffic gets over the interface witch passes the traffic through. what kind of routing protocol could i use on a 3550er? if this should workout.

May I ask why you want to do that? Perhaps there is a better solution to what you are trying to do.

we got a vtp server in building A, and some departements in building B. both buildings need the same vlan definitions. the buildings are connected like the picture i put the link in the previous posts. now with fogy weather we got some real problems. And for that reason we need a automatic failover system. Spanntree does not workout for this, and so does etherchannel.

now, thats what im looking for ;-)

Picture:

Unless there is something very siginificant about your network setup that is not reflected in the graphics, I still don't understand why you need the same vlans in both locations. Each 3550 can be a vtp server for the location it is at. Don't use vlans between them, use L3 and a routing protocol. The routing protocol can be your failover. The end devices will be on separate subnets. Or, is there a reason that both ends will need to share a vlan/subnet? I'm not a fan of broadcasting over WAN links.

Jim

How often does your vlans change? How often do you delete or add vlans? It is a common thing to disable vtp because it can do much more trouble in networks than it makes administration easier.

I would still use L3 for laser and backup links and do the following:

If you need to have the same broadcast domains and still have routers in between, why not try to use GRE tunnel for every VLAN and do a bridging between VLAN and GRE? I've never tried it, but it might work (if I get some time, I will try it)....

we want to keep administration as little as possible. we get our vlan definitions from the main building, vlans change pretty fast at our place, so there is a lot of changes, and nobody likes to do the hole configs twice or three times... there are several buildings attached the same way via laser!

its about 250 up to 500 meters laser line ;-)

@ Ivan

what do i need for this suggestion?

another question about spanntree, what happens if you build up two 3550er connect each from fa0/1 to fa0/1 and fa0/2 to fa0/2. now each fa0/1 is in vlan 10 and fa0/2 is in vlan20. as vlan ip one would have a 192.168.10.2 the other .3 or of course for vlan 20 192.168.20.X would spanntree block one side or would both sides be up? physical its a loop, but since there are 2 diffrent vlans? since i then would have a layer 3 ip on the other side would this then not be posible to route it?

That should work ok.

There would be two different spanning trees (if using PVST) so both links should forward traffic.

IP address on vlan and physical interface are different things. You need vlan 1 to push vtp between switches. This might get really complex. You should probably search for some good consultant which has experience with such setup.

you said it should work, because there 2 spanntrees (VL10 / VL20), but what about vlan 1? !! there would be aloop not?

indeed i'm looking for one! or a way how to simulate my stuff.

hmm, ok, lets take a look at this MPLS suggestion.....

No, in vlan 1 some ports would be blocked to keep out of loops.

It's hard to find a good one...

MPLS solution would not be feasible in your envirnoment. I've recommended is as a transport solution while I haven't seen "the picture", so I belive this solution is out.