This is our old Q&A Site. Please post any new questions and answers at

Hi folks!

I have a strange issue. It seems that the GSM packets which I filter out by gsm_map are shown twice, as appears in the below screenshot: alt text

I use the following command from command line to capture the traffic:

tcpdump -i any -s0 -w test.cap

Any clue why such behavior could occur?


asked 19 Apr '12, 07:47

Eugene%20S's gravatar image

Eugene S
accept rate: 0%

If you are capturing of an interface connected to a monitor/span port of a switch you might get packets written to your trace file twice ingress/egress depending on how you have set up your monitoring.

permanent link

answered 19 Apr '12, 09:23

Anders's gravatar image

Anders ♦
accept rate: 17%


...or if you capture on the "any" interface of a Linux-based router and the traffic shows up on multiple physical interfaces.

(19 Apr '12, 10:16) Gerald Combs ♦♦

@Anders and @Gerald Combs, thanks a lot for your comments! However I'm still a novice in this area and I'm not sure I understand your answers completely. Could you please provide a bit more details about what causing this behavior and how to solve this problem. Maybe you can provide some links for further reading.. Thanks again!

(20 Apr '12, 01:32) Eugene S
Your answer
toggle preview

Follow this question

By Email:

Once you sign in you will be able to subscribe for any updates here



Answers and Comments

Markdown Basics

  • *italic* or _italic_
  • **bold** or __bold__
  • link:[text]( "title")
  • image?![alt text](/path/img.jpg "title")
  • numbered list: 1. Foo 2. Bar
  • to add a line break simply add two spaces to where you would like the new line to be.
  • basic HTML tags are also supported

Question tags:


question asked: 19 Apr '12, 07:47

question was seen: 5,509 times

last updated: 20 Apr '12, 01:32

p​o​w​e​r​e​d by O​S​Q​A