We we use Layer 2 or Layer 3 as a medium to route traffic

[Loc120287]

Hi,

I have a client has network degin similar to Option A as below:

It use a route subnet 10.33.201.0/8 for Routers that do routing job.
R1, R2,R3,R4 have Layer 2 connection with each others
Route uses EIRGP

I wonder if it is better if we use option B: 

Option B: use point to point /30 for each connection between two Routers
Route uses EIRGP

I think Option A better because it use Layer 2 CEF to forward packets while Opion B Router need to route packets. 

All Routers here are actually Cisco Layer 3 switches.

Could you advise?

Thanks

Loc

[MHM Cisco World]

For me using L3 öp B is better

Because l2 is hard to troubleshooting if something happen. 

So go with L3. 

For cef both use cef. 

MHM

[Flavio Miranda]

@Loc120287 

 I dont think option A uses Layer2 CEF. They are acting as router not switches as they have routing table and ip address and routing protocol. They will use Layer3 CEF.

 There will always be layer2 connection even though you were working with Router. 

 The advantage of option A is that,  in the event you need to work with vlan and trunk, that scenario would allow it. One disavantage is that there will be spanning-tree running on that topology and if you change the topology you may be risking a loop.

If routing is the only goal, option B seems to be better in my opinion. 

[Joseph W. Doherty]

"I dont think option A uses Layer2 CEF."

Actually, there's no L2 CEF (to my knowledge).

"They are acting as router not switches as they have routing table and ip address and routing protocol. They will use Layer3 CEF."

Correct for R1 and R4, but in option A, R2 and R3 will pass transit traffic just like a L2 switch.

[Joseph W. Doherty]

In practice, a L3 switch forwards L3 just as about as quickly as it does for L2.  So, R2 and R3 would benefit very, very little doing L2 rather than L3, regarding forwarding performance.

There are more issues that might be considered between the two approaches, from broadcast issues within a L2 domain, to size of route tables, to multicast (route) flooding, trouble shooting (as mentioned by @MHM Cisco World ), etc.  Usually such issues, their cost vs. benefit, favor L3.

Of course, for the topology shown, if the decision was whether to purchase more expensive L3 switches, rather than less expensive L2 switches, possibly that would be a valid reason to use option A, but if you already have L3 switches, again, L3 designs usually are "better".