3

Given:

  • A typical collapsed core design where there are X number of L3 access switches connected to one L3 distribution switch.
  • VLAN trunking is enabled between the various AS and the DS.
  • A router that is the default gateway is connected to the DS.

Should the GW on the clients connected to various AS be set to a VLAN subinterface on the specific AS they are connected to?

Or, should the GW for all be set to a VLAN subinterface on the DS?

I think the latter, but I am uncertain that my understanding is complete.

1
  • Did the answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. – Ron Maupin Aug 1 '17 at 12:40
1

The host gateways needs to be set to the gateway, which is the address on that network of the device that will route traffic to other networks.

If your access switches are running layer-3, then they should be using routed links to a layer-3 distribution switch. That means the distribution switch does not have addresses in the access networks.

If your access switches are only running at layer-2 (even if they are layer-3 switches), then you have trunks to the layer-3 distribution switch, and the gateway for a client would be the address in its network of the layer-3 distribution switch.

What you really don't want to do is to trunk all the networks to all the switches and set up all the access and distribution switches as layer-3 switches on all the networks. That really defeats the whole purpose of using layer-3 in the first place.

2
  • If I understand what you are saying, we should either route everything with no trunks - or, trunk from each AS to the DS and route only in the DS. Correct? – Xevious Mar 4 '17 at 14:52
  • Right. If you put a bunch of gateways on the networks, you are really creating problems. You will certainly have asymmetric routing, and that could be a source of problems. A newer best practice is to run layer-3 on the access switches up to the distribution switch, with layer-2 to the hosts. This eliminates STP problems. If you use layer-2 from the access switches to the distribution switch, then you should limit a VLAN to a single switch. You can have multiple VLANs on a switch, but they will not extend to any other switch. This also eliminates STP problems. – Ron Maupin Mar 4 '17 at 15:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.