layer 3 connection between core and distribution switch

[CSCO12233236]

Hello everyone,

Could someone please guide me on how to set up a layer 3 connection between a distribution layer and core layer switch?

The way I understand is that in order to set up a layer 3 link, the port needs to be a routed port. Does that mean that on distribution switch, it also needs to be a routed port?

If the port is acting as a routed port, do both ports on the each switch needs to be on the same subnet?  If I have suppose 30 vlans terminating on a distribution switch, how do I advertise them to a core switch through a routed layer 3 link?

A sample configuration of creating a layer 3 link between switches would be greatly appreciated.

Thank you gentlemen.

[Jon Marshall]

Doesn't have to be a routed port but it is best to make it one.

Basic configuration at either end of the link -

int <num>
no switchport
ip address x.x.x.x <subnet mask>

usually the subnet mask is 255.255.255.252 as you only need two useable IPs.

You advertise the IP subnets either using static routes or run a dynamic routing protocol.

If you use statics then the next hop IP is the IP address of the other end of the L3 link.

Jon

[CSCO12233236]

Thanks Jon

Much appreciated!!

[Reza Sharifi]

Hi,

Yes, you need a /30 (routed port) between the distro and the core switch and they need to be on the same subnet. Or you can use SVIs.

example:

on distro switch

interface gi0/1

no switchport

ip address 10.10.10.1 255.255.255.252

on core switch

interface gi1/1

no switchport

ip address 10.10.10.2 255.255.255.252

To advertise all 30 vlans from the distro to the core, you can simply turn on OSPF on both distro and core and add the above /30 to OSPF.  Once this step is complete, you should see OSPF peering between the distro and the core.  Verify with "sh  ip os nei"

after the peering is established on the distro switch add all 30 vlans to OSPF as passive. Now you should see all vlans on the core.  Verify with "sh ip route".

HTH

[CSCO12233236]

Thanks for the input Reza

Also, if I want the vlans to communicate on distro, I should simply set up layer 3 routing on distro and create SvI's.  Finally I should use an IGRP to advertise the vlans into core.  I really don't need to define the vlans on the core switch. Do I?

Muhammed