[c-nsp] vlan across a routed link

[Oliver Boehmer (oboehmer)]

> teklay gebremichael wrote:
> > i work in a university which has three campuses. on each campuse,
> > there is one cisco 6509 switch as a core switch. all other switches
> > (L2) are in vtp client except the core switches. the campuses are
> > connected with a routed link. so, one campuse, has 10.128.0.0/16
> > subnet and the others have a subnet of 10.129.0.0/16 and
> > 10.130.0.0/16. rip v2 is used on the intercampuse links to advertise
> > individaul vlans.
> >
> > here is my problem.
> >
> > i'm asked to create a vlan with a subnet id of 192.168.1.0/24. but
> > computers in this vlan are located in the 10.128.0.0/16 campuse and
> > 10.130.0.0/16 campuse.the link between the 10.128.0.0/16 and
> > 10.130.0.0/16 is not trunk it is routed with ip address. so can any
> > body suggest me how to implement such senario which allows one vlan
> > (in this case 192.168.1.0/24) to be visible from the two campuses?
> > i.e to propage that specific valn across a routed link not a trunk
> > link. thanks
> 
> You will need to convert the link from routed to switchport. That is,
> transform this:

right, but think about the implications before doing so. You will extend
your spanning tree domain over all the different sites, so this just
asks for disaster to happen. And don't mention "hey, I only do this for
a single Vlan". Once you start offering this "service", users will ask
for it, and you end up doing this for many.

Please consider technologies for this where you don't need to extend
spanning tree. for example L2VPN (EoMPLS, VPLS), or loop-free topologies
using VSS where you can disable STP between campuses..

	oli