IP routing with multi-layer switch

[dellpe]

I've read many IP routing examples where a single Layer 3 switch like S5700-28C-SI is used as the router in a network environment where all other switches are operating just at Layer 2. That's fine, I understand that.

However, what about if one has many Layer 3 switches?

Does one (a) simply choose one of the Layer 3 switches to be the router, or (b) do something more cunning, making use of the Layer 3 facilities of the other switches?

In the networks I'd be working in, the ports associated with each VLAN are fairly evenly scattered across all switches.

My thoughts on this stem from this problem: If one uses the simple approach of Choose Just One Switch To Be The Router, then all cross-VLAN traffic needs to pass across the LAN to that switch in order for routing to take place, which seems inefficient. As the size of the LAN grows, it becomes increasingly inefficient.

So, is the Just Choose One Switch To Be The Router approach the only option?

 

[theonlyski]

In the networks I'd be working in, the ports associated with each VLAN are fairly evenly scattered across all switches.

My thoughts on this stem from this problem: If one uses the simple approach of Choose Just One Switch To Be The Router, then all cross-VLAN traffic needs to pass across the LAN to that switch in order for routing to take place, which seems inefficient. As the size of the LAN grows, it becomes increasingly inefficient.

Well, if you have say vlan 10, 20, 30 and 40 and have 4-5 switches:

If all of the hosts for vlan 10 are on one switch, all of the hosts for vlan 20 are on another and so on and so forth, then enabling ip routing on each switch would work fine and keep the 'chatter' on the links down.

If you have several hosts from each vlan on each switch, then it would make more sense from a KISS principle to just use one switch doing layer-3 and home run each switch to it (if possible). This would also make restricting inter-vlan access easier (one choke point to manage).

 

[theonlyski]

So, is the Just Choose One Switch To Be The Router approach the only option?

Nope, but depending on your topology it may be a good option.

 

[stevech]

In consumer space, ethernet switches are not routers.