My customer has bought a layer 2 WAN service from a service provider and already purchased 3750 switches to act as CE devices. They now want me to specify a design of how to implement what they have bought. They have about 50 sites but due to QoS limitations of the service provider they need to use 1 physical interface to route voice traffic towards the WAN at each site and a different interface for data traffic. They wish to have a dynamic routing environment so in my opinion they have two basic options for routing protocols that could send the voice and data out of different interfaces:-
1) Run EIGRP and use distribute lists to advertise voice subnets out of 1 link and data subnets out of the other.
2) Run 2 different routing protocols, e.g. OSPF for data and EIGRP for voice. I don't think there should be any need to redistribute between them.
I think that either of these solutions is likely to give me scalability issues due to the number of neighbors required (ie approximately 100 per switch) but I haven't managed to find any numbers for what should be achievable. Can anyone give me any indication of the likely number of eigrp neighbors I could reasonably support? I have seen some people mention best practice is 20 but I have also seen references to a Networkers presentation where they discussed a live environment with 800 neighbors on a 7200.
I have also been considering ways to improve scalability. I have identified the following:-
1) Most sites can run as stubs because there is only a single switch per site.
2) I am not sure yet but I am hoping that the LAN addresses within the sites can be summarised towards the WAN so instability in the LAN will not cause instability in the WAN.
3) I think I could possibly reduce the number of neighbors required on some devices by configuring static neighbors and configuring switches at key sites as hubs for the smaller sites. I think this would probably require me to turn off split horizon. I think I could also use the 'no ip next-hop-self eigrp' command to stop traffic having to route via the hub site. I am nervous of turning off split horizon and using this command in an environment with multiple hubs. Please could you give me any guidance?
4) I could implement multiple VLANs within the WAN and implement a hierarchical design over the top of the layer 2 WAN. I am sure I could get a solution like this to work and it is the one I will most likely fall back on if I don't get an answer to this query, but the exact solution would also depend on how many neighbors I could configure on the 3750s. The main problem with this solution, however, is that traffic will route via the hub sites rather than going directly to the destination site. This will cause an overhead on the WAN connections at the key sites, which is exactly where I don't want it.
Failing all of the above, I could push back on the customer's requirement to have dynamic routing and suggest static routing over half or all of the network. I obviously don't want to do this if these is a feasible solution.
All suggestions appreciated.