[j-nsp] Layer 2 ethernet redundancy?

[Jeff Wheeler]

On Wed, 2004-01-21 at 21:50, Tony Frank wrote:
> The specific concerns I guess are more to do with the practice of having the
> two interfaces into separate switches carrying the same logical vlan.
> 
> eg other routers have only single interface, so it's simple to use the 
> interface IP as the BGP neighbour address - if either interface or router
> fails the path is gone (and BGP goes away)
> 
> On m20 we have two interfaces with two IP.
> Currently we spread the BGP sessions across the two interface IP addresses.
> Another point that was not mentioned originally is that each 'customer' has
> two routers, one on each l2 switch.

Perhaps you can explain more comprehensively how your BGP sessions are
setup from your m20 to your routers. I don't understand your problem as
well as I'd like, but I'm willing to bet that layer 2 redundancy on your
m20 is not what you actually need.

Seems to me like your "routers" 1 - 4 should be speaking BGP to your
m20s on loopback addresses which participate in your IGP, for example
OSPF / ISIS / RIP2. In this instance, it doesn't matter if one of your
FE interfaces fails, because you'll have two or more layer 3 subnets on
different physical interfaces participating in your IGP, and any of
those can and will carry the route to your loopback address.

This is what your IGP is for. Do you have one now? If not, get one. Pick
OSPF because it works with a lot of devices, unless you are already more
familar with another IGP that you prefer over OSPF. No holy war, please.

When you follow-up, include example AS numbers for "routers" 1 - 4. If
you are using a route-reflector or confederation, send details on that
as well. You will probably be asking more specific questions that will
be best answered if the list readership understands your topology.

-- 
Jeff at Reflected Networks