Best way to find which networks I will need to include in ospf

[news2010a]

Good morning!

Imagine I have a Cat-3550-Old switch. Currently switch is configured with "ip default-gateway <IP_ExternalRouterDoingLayer3>. Such Cat-3550 switch is currently doing Layer 2 only.

My task:

I need to replace this switch Cat-3550-Old with a Cat-3750-new. I will make the Cat-3750-new do Layer 3 instead.

I should keep all existing VLAN configuration, routes, etc and keep my internal LAN workstations pointing to the same default gateway (currently the ip default-gateway IP.

My question is:

I see that I have only vlan1 and vlan2 configured with IP addresses in my Cat-3550-old.

I mean, considering that I have to make Cat-3750-new route the same networks the existing configuration is routing, is it right to assume that I only need to include in my 'route ospf #' network <defined_for_vlan1> and network <defined_for_Vlan2>. I would also include a loopback0 related network (which is not currently configured in the cat-3550-old switch).

I am just trying to see if there is an intelligent method to determine which networks I will need to include in order to cause minimal disruption when I get this replaced.

Thanks!!

[akachroo123 · Accepted solution]

Yes, you need to include network(Vlan1), Network(Vlan2)and loopback under Ospf.

Also you need to configure default gateway as the ip address configured under Vlan1 or Vlan2 on your LAN workstations depending upon the Vlan to which they belong.

Now you dont require ip default-gateway command on new switch.

Arun