Is loopback interfaces required for ospf?

[Keith9]

In Cisco world, you want to create a loopback IP address and advertise it in OSPF.  It's a virtual interface thats never down.

In EXOS however, it's a little different.  Vlan1 for example, isn't "down" if there are no active ports in it.  Is it still recommended to create a Loopback IP even if we already set a router ID, and advertise it in OSPF as a /32?


I mean I can hit a switch at its mgmt IP 10.1.0.254 for example, or also hit it via its Loopback 192.168.255.1 and OSPF finds the way to it either way.  The Loopback 192.168.255.1 in this example just seems redundant.

[Gabriel_G · Accepted solution]

Hello!

"Vlan1 for example, isn't "down" if there are no active ports in it."
-> This is incorrect. A VLAN with no active ports is operationally 'disabled' or 'down' unless loopback-mode has been enabled for that VLAN(enable loopback-mode vlan <VLAN>). This implies that a VLAN/Subnet with no active ports in it is not advertised to OSPF unless loopback-mode is enabled. This can be seen in 'show iproute' as the route to that directly connected VLAN with no active ports is not active (#).

"Is it still recommended to create a Loopback IP even if we already set a router ID, and advertise it in OSPF as a /32?"

-> A routerID is not advertised as a route to OSPF. If you want the IP that is the same as the routerID to be reachable/pingable, you would want to make a loopback VLAN that has the same IP as the routerID, enable loopback-mode for that VLAN, and add it to OSPF.

Hope that helps!