L2 vs L3 between 1002 and 3750X Core

[Patrick McHenry]

Hi,

we are replacing network equipment at one of our sites. The network will have 12, 3750X switches(6 stacks) - one stack will be the core. A 1002 will be the WAN router to the Main campus. The 1002 will connect to the core via 2 ethernet cables. I'm debating whether to use L3 or L2 between the router and Core. I've heard that routing is more efficient if L3 is used and also I will be able to create an L3 etherchannel  between the 1002 and Core switch. See the attached doc.

Does anyone have any docs on the subject or comparisons.

Any opinions would be appreciated.

Thank you, Pat.

[Reza Sharifi]

Hi Pat,

Since you connecting to a router (1002), you would need a layer-3 Etherchannel using LACP.

routers usually don't support layer-2 Etherchannel.

see example in this link:

http://www.cisco.com/en/US/docs/ios/ios_xe/cether/configuration/guide/ce_lnkbndl_xe.html

HTH

[Patrick McHenry]

Reza

Yes but, I could just use one of the links as a backup and have the switch interfaces connecting to the router be a layer 2 switchport. The router interface could be the gateway for the connecting VLAN.

My question is should I make the switchport connecting to the router a layer 2 interface and connect as I just mentioned or should I create a /30 network between the router and the switchport? I've heard that traffic flows more efficiently this way.

Thank you, Pat.

[Reza Sharifi]

Pat,

I go with Layer-3. This way no need for stp.

HTH

Reza

[Patrick McHenry]

Reza,

I'm going to need to use spanning tree on the switches but anyway, if the switchports connecting to the router were layer 2, spanning-tree wouldn't come into play on those ports because I would configure one of the router interfaces as a backup. I'm really after what is most efficient and what is best practices as far as the config between the router and switch? Layer 3, /30 network between them or, switchports as layer 2 and router as gateway to a VLAN on the switch.

Thank you, Pat.

[Reza Sharifi · Accepted solution]

Pat,

In you design the 3750s are your layer-2/ layer-3 boundaries with SVIs on the 3750 stack switches.  Conversation between vlans will be routed using the 3750s.  If you make the link between the stack and the router layer-2, you will need to extend all your vlans all the way to the router and there is no need for that.  In addition, switches are usually faster then routers. So, I would keep the intervaln routing on the 3750s and have a /30 with portchannel between the 3750s and the router.

HTH

Reza

[Patrick McHenry]

Thanks Reza