Default Route vs IP Default Gateway

[Mokhalil82]

Hi 

Now I know a default route works on L3 and IP Default Gateway on L2. What I want to know is can I use both on a L3 switch which is enabled for routing, i have this setup, please see attachment

So both 3750 switches have a default route to their gateways. Switch at site 2 also has a ip default-gateway statement pointing to the switch at site 1. 

Will the switch at site 2 pass layer2 traffic to site1 and forward any layer3 traffic to its gateway. Thats the objective

So the access switches at both sites are using the gateway at site 1 for external traffic, when the external link at site 1 fails it needs to be routed to site 2. The question is not regarding the failover but instead will traffic at L2 just route through the switch at site 2 to site one under normal operation

Thanks

[Jon Marshall · Accepted solution]

It doesn't really work that way but it doesn't need to.

If switch is sending traffic within the same vlan/IP subnet then it doesn't need a default gateway or a default route because you only need those to send traffic to another IP subnet.

If the switch is sending traffic to another IP subnet then if it is a L2 switch it simply sends it to it's default gateway.

If it is a L3 switch it uses the default route.

So you only need one or the other and if your switch is acting as a L3 switch it should be the default route.

Jon

[Mokhalil82]

Thanks Jon

I was making sure that the L2 traffic will just pass through the switch at site 2 to site 1. It is just acting as a transit switch for L2 traffic.