Benefit/reason for setting Loopback address on Interface? 1

[GeneralDzur]

Is there a benefit or reason to set a loopback address on an interface?

The only thing I could think of was to use PBR to route illegal traffic to a null address?

- stephan the confused

 

[lambent]

Imagine you have multiple paths to reach your router. If you use an IP address of one of the physical/sub-interfaces to use as...say router-id of your routing protocols, SNMP source, or whatever processes, when that particular interface is down, all of these processes will not work even if you have redundant paths to reach the router. That's why we need loopback since it's always on.

If you have just 1 outgoing interface then loopback may not help in this case, but it's always harmless to set one. Take it as one of the best practices.

 

[GeneralDzur]

Oh, ok thanks. Like you said, we have a single link to the internet (e1/0). Should my loopback address be the same as the Interface's IP address?

Also, change of topic, but set the Interfaces bandwidth to 2048 Kbits/sec, because that's what our ISP's d-load rate is. I then changed the queueing method to WFQ. Any thoughts on that?

- stephan

 

[lambent]

for the loopback, give it a different IP subnet

Usually we use a /32 mask for that. Say your network has 10.0.0.0/24 and 10.0.1.0/24, then assign one more subnet 10.254.0.0/24 for the loopback of all devices. E.g. 10.254.0.1/32 for Router1, 10.254.0.2/32 for Router2...etc.

For QOS, it depends whether you want to shape outbound traffic or police inbound traffic. Also there are additional options on frame-relay traffic shaping. And as of 12.2 we can even have nested class-based policy-maps so that you can use shaping on the parent policy-map and CBWFQ on the child maps.

But....if you do this on low-end routers, your CPU utilization may burst above 50%. You can try it if you feel comfortable with this 50% threshold.

And by the way, WFQ seems to be the default queueing mechanism on serial links with <=2Mbps. It's just a little bit better than FIFO I believe.