Loopback address

Unanswered Question
Jun 19th, 2008

ok I thought I fully understood the use of loopback addresses but I have one question I notice during an IP accounting I see that my core routers loopback address talk to the edge routers loopback address. the question is what is the reason why the loopback addresses would be talking to each other?

I mean when I do an IP accounting I see the source as my core router loopback and the destination is one of the edge routers loopback address. At first I thought this is because of the tacacs and logginging purposes but then I see the edge loopback addresses going to the tacacs server ip address so not sure why there is a loopback to loopback communication on the routers with each other?

Thank you in advance

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Edison Ortiz Thu, 06/19/2008 - 05:50

Very hard to tell without seeing the actual configuration but for instance with BGP, you can configure neighbors to source from their loopbacks and point to remote device's loopback.

Perhaps, that's the traffic you are seeing if you have BGP configured.

As a side note, I recommend implementing NetFlow instead of IP Accounting as NetFlow is more descriptive on the type of traffic flow traversing the interface.




wgranada1 Thu, 06/19/2008 - 05:55

There is no BGP configured, they are all connected via frame relay circuits. I will try Netflow as you suggested and see what kind of traffic is going between the loopback addresses.

Kevin Dorrell Thu, 06/19/2008 - 06:48

It could be anything really. NTP perhaps? Is the core router providing an NTP service with its loopback address as the source?

Kevin Dorrell


wgranada1 Thu, 06/19/2008 - 07:05

Your probably right as I went on one of the edge router to check NTP:

ntp server source Loopback0

ntp server source Loopback0

and the above are the loopback0 address of the 2 core routers


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