[SOLVED] Empty lines in output of tcpdump

hua · 05-17-2012, 08:20 AM

I can see strange output of tcpdump. Occasionally I use the tcpdump to monitor the network traffic. I am on the public net and connecting to the server with ssh so my command is:

Code:

tcpdump not port 22 and not multicast

The network has a huge multicast traffic so I filter this out and the ssh too.
The output contains cca. 5-10% of empty lines. The line contains only the date and time and nothing more. What can cause this?
This is the sample of the empty lines:

Code:

15:18:10.195434
15:18:20.195831
15:18:30.196248
15:18:40.196659

nikmit · 05-17-2012, 08:31 AM

See the mac of the sending machine by adding -e to your command line.
I believe they are cisco loopback packets - see https://supportforums.cisco.com/thread/5466

hua · 05-23-2012, 01:00 AM

Quote:

Originally Posted by nikmit

See the mac of the sending machine by adding -e to your command line.
I believe they are cisco loopback packets - see https://supportforums.cisco.com/thread/5466

Thank you it works and those packets are exactly as you told.