Collapsed Core - Use Layer2 or Layer3 between Core/Access?

[tylerlucas]

Using two 3750's for the core. 

There are several routers connected - 1 with a PRI, 2 for MPLS, and a couple firewalls for internet access. 

Is it best practice to have these all connect to the 3750s using access links, or layer 3 /30 links and OSPF?

Or is it just personal preference?  I'm trying to keep scalability in mind.

[Reza Sharifi]

Whenever you can, it is a good idea to use routed interfaces with point-to-point /30s segments.  This way, you don't have to worry about VLAN, STP, BPDUs, etc...It also scales better.

HTH

Reza

[tylerlucas]

Reza - thanks for the response.

I plan on connecting a 2801 to my 3750 stack.  Since Etherchannel is not supported, what is the best way to connect this using multiple links (one to each switch)? Is this a typical setup? Or is the common solution to use a 2nd 2801 and configure HSRP?

Thanks again.

Mzinz

[Reza Sharifi]

Mzinz,

I would install a  2nd 2801 and do HSRP or VRRP.  This way, you have both switch redundancy and router redundancy.

Good Luck

Reza

[Dan-Ciprian Cicioiu]

Hi ,

I would install a second 2801 and a routing protocol without HSPR/VRRP, between the core and the wan router.

If you want to stick with the ideea of routed port and /30 class between the core and the edge wan router.

Dan

[tylerlucas]

Thanks again for the replies.

If I connect two 2801's to the 3750 stack using routed links, they must be in different subnets (so the switch doesn't have two L3 interfaces in the same subnet).  Since the interfaces are in different subnets, I can't do HSRP on the routers.

EDIT: Is it only possible to do HSRP when connected through a (L2) switch?

Thanks again,

Mzinz

[Dan-Ciprian Cicioiu]

Hi Mzinz,

The interfaces of the two devices that are configured for HSRP must comunicate with each other on layer 2.

So in the case of the routers, you will need a layer 2 connection (vlan) between the routers interfaces.

Dan