Geek Speak

The value of manging via loopback addresses...

I got involved in a conversation at the whiteboard the other day where we were talking about the value of managing network devices via their loopback address. It occurs to me that this may be a best practice that many of you haven't implemented so I thought I'd write a little bit about why it's important and how it can help you.

For the sake of keeping things simple, let's talk about managing/monitoring routers. As you know, a router will typically have several IP addresses - at least one per interface and you can usually use any of these addresses to communicate with the router from your NMS. Now, let's assume that you use the IP address of interface serial 1/0/1.1 for monitoring of the device. What happens if that interface is down? Suddenly, your NMS thinks that the entire device is offline and you'll get alerts that the router is down and the NMS will stop collecting the data for the other interfaces as well as the router level statistics like latency, CPU, memory, and buffer usage.

So, how do you get around this issue? You implement a loopback addresss on all of your routers and you be sure that these addresses are reachable throughout the network. A loopback address is basically a virtual interface at the core of the device. As long as you have a path to the device, the loopback address should be reachable.

This best practice can save you a lot of time and effort down the road if you implement the loopback addresses before upgrading or deploying a new NMS.


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Published Sep 30 2008, 10:13 AM by Josh Stephens

Comments

 

redpineapple said:

I agree 100%. Loop addresses are easier to secure and make more sense in a table. Also if you change interfaces in a router there is no reconfiguration required. Sometimes it might be required to shape or police NMS traffic and this makes the task easier. However, you need to configure the router to tell it to use the loopback address for SNMP or your traps won't be associated with the router in your NMS!
October 1, 2008 1:38 PM
 

Josh Stephens said:

Great point. You should also think about this when sourcing NetFlow/SFlow traffic...

Josh

October 2, 2008 2:35 PM
 

jswan said:

There's lots of weird stuff that can happen if you don't configure your management protocols to source from the loopback address. Here's my usual template: ip ssh source-interface Loopback0 ip urlfilter source-interface Loopback0 ip flow-export source Loopback0 ip tacacs source-interface Loopback0 ip radius source-interface Loopback0 logging source-interface Loopback0 snmp-server trap-source Loopback0 ntp source Loopback0
November 13, 2008 12:28 PM

About Josh Stephens

Josh Stephens is a Vice President – and Head Geek – at SolarWinds, where he plays an integral part in the development and delivery of our award-winning network management products. Josh has extensive experience in network management systems, network engineering, and software development. His 15-plus years of experience in technology include designing and deploying advanced networks and network management systems within organizations including the US Air Force, Sprint, MCI/UUNET, and Wal-Mart. He has received several industry certifications including those from Cisco Systems, Microsoft, and HP.