[c-nsp] Router or Layer3 Switch

[Justin Shore]

Duracom Lists wrote:
> Arie thanks for the information.  I have another thing before I make a
> decision.  I have my network setup as follows:
> 
> 7206VXR
> Int f0/0 has several (50 or so) /28 subnets 
> 
> F0/0 <--------> 2950 port 1
> 
> Now if I had a L3 Switch (in place of the 2950) can an interface on an L3
> switch have multiple subnets?  If I put a router in place of the 2950 switch
> I could easily define multiple subnets per Interface like I do on my edge
> router. I am just trying to look for the best way to do this since I have
> never dealt with any L3 switches.

You could create "routed" interfaces on the L3 switch which is where you 
assign an IP to the physical interface (no switchport).  You could also 
create SVIs or Switch Virtual Interfaces.  These are the layer-3 
interfaces for VLANs.  Then you assign the VLAN to the physical 
interface (switchport access vlan X).

I'm not aware of any performance problems between the 2 options.  I 
utilize both methods.  One problem with SVIs is that support for BFD on 
SVIs is questionable (see recent threads).  If you aren't using BFS then 
that doesn't matter.  SVIs would allow you to assign multiple physical 
interfaces to the same VLAN obviously so that may be useful depending on 
your needs.  The SVI option would also let you create 802.1Q trunks for 
attaching multiple VLANs to a single physical interface.  Depending on 
your wireless backhaul radios you might be able to carry 1Q trunks over 
them.  Again that depends on your needs.

When you run low on physical interfaces on your L3 switch (assuming you 
buy a 3750 of some sort) you can introduce another L3 switch to create a 
stack using Cisco's StackWise-compliant switches (3750, 3750E, maybe the 
ME3750 plus some EtherSwitch *Service* Modules for the ISRs)

Justin