Core Switch Addressing

[Bakedgoods]

When you are using a layer 3 switch as your core, will each interface have its own address like it would on a typical router?

For example, a router occupying the last address on every sub network.

 

[bigredshark]

If the core switch is the only layer3 switch then yes, each interface leading to the l2 distribution/access switches will have the gateway address for that subnet. If the distribution/access switches are L3 as well then typically you'd have a /30 range linking them to the core switch and the gateway would be on the local switches.

 

[Bakedgoods]

The core is a 3 switch stack, which heads out to the L2 access switches. The only thing above the core is a router with a wan connection.

 

[dantheman213]

There are possibly 3 ways you could do this, all depends on whether your access switches can handle L3 or whether you simply want to run them at L2:

-On the core switch, you'd create multiple L3 vlans (eg default gateway for all the vlans on the access switches), then simply trunk the port from the core switch to the access switch, this way you're not limited to only having a single vlan on the access switch.

-Have a /30 connection between the core and access switches (1 interface on the core switch per access switch), and create the L3 vlans on the access switch, this would depend on whether the access switch can handle L3. Could also get a little messy as you'd possibly have routing going on within the access switches.

-Each interface on the core switch would have a L3 address and connect to the access switch, all devices connected to the access switch would then use the L3 address on the core switch interface as their default gateway. Limited to only a single vlan on the access switches though.

Limitation of the bottom 2 options is that you'll only be able to run a single vlan on the access switches, whereas the top option gives you the chance to have multiple vlans, which you'd need if you had IP phones etc.

Personally, I'd use option 1. Hope this helps......

 

[oddjob62]

I would have thought if your access layer switches are L3, you would be better with option 2, allowing for pure routing between the access and core. This would allow load balancing between equal cost paths, and remove the need for (wasteful) redundant links caused by using STP. Also convergence would be quicker (from what i've read) in the case of a broken link.

Option 2 should still give you the option to use multiple vlans (eg for voip), unless i've read dan's description totally wrong, it would just mean that the vlans are localized to the access switches.

Please correct me if i am way off in my train of thought.... should be in bed by now