ATMARP (loopback) Frames being broadcast – Cisco Catalyst 3750 12.2-40 (advipservicesk9)   Leave a comment

I’ve noticed one of my switches is broadcasting ATMARP frames every 10 seconds to all switchports.. I had no idea why, as the switch has no ATM interfaces (naturally) nor does the IOS support ATM/LANE. CDP and STP was disabled.

I think these frames are being mis-decoded in Network Monitor – they also showed as loopback frames in the trace (even though classified as ATMARP), which led me to this page

Aha! These frames are sent by default every 10 secs on each ethernet interface as a soft connectivity testing mechanism.

This is an example of someone seeing this kind of traffic –

To disable an interface’s soft loopback diagnostic frame capability, configure "no keepalives" on the interface.

The downside to configuring this is the interface will always show UP/UP when any media is connected – speed/duplex issues will not trigger UP/DOWN.

Wonderful mysteries and magics of IT :)


Posted May 28, 2008 by benryanau in Cisco

Tagged with ,

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: