Layer 3 IP routing with bridging between VLANs for DECnet

dave.thornton · ‎10-26-2001

Suppose a CAT4006 with 2 VLANs (and 2 IP subnets)

also has a Layer 3 router blade WS-X4232-L3 which is routing IP between the VLANs.

Now suppose a non routable protocol like LAT or DECnet requires bridging *BETWEEN* vlans?

Is this possible? what are the issues if any?

thanks

dave

bfeeny · ‎10-26-2001

Yes this is possible. What you want to happen is for some protocols to be routed (IP for instance) and others to be bridged (DECnet for example). Read up on CCO about Integrated Routing and Bridging (IRB). It involves the use of BVI's (Bridged Virtual Interfaces) and using "bridge-groups". There is alot of good information on CCO regarding this, possibly even a cookbook recipe for what you're trying to do.

Brian

ajay.singh · ‎10-29-2001

Dave,

You do not need to bridge in order to route DECNET. Just enable the decnet protocol and then assign a cost to a particular VLAN interface.

If you want to bridge LAT traffic you can use bridge group and assign the two bridge interfaces to a bridge group. But be careful of the spanning tree topology. By bridging two VLAN interfaces you might create a loop, spanning tree will shutdown one of the links which may not be one that you want to be turned off. Other than this, LAT kinds of defeats the purpose of a VLAN. Best thing to do is to keep the Terminal Servers and VAXes in the same VLAN. This is fairly easy because all you have to do it is to make the port that the terminal server is attached to belong to the same VLAN as the host VAX.

I have implemented this in my designs and it works perfectly. Please send me e-mail if you have any questions. Thanks,

Warm Regards,

Ajay Singh.

rfroom · ‎10-29-2001

DECnet routing is not supported on the 4232-L3 and you will have to bridge between the VLANs. Keep in mind, that when you bridge between VLANs you will create a single instance of the IEEE STP. Make sure the router is the root bridge for the Spanning-tree Topology.