Linux, FreeBSD, Juniper, Cisco / Network security articles and troubleshooting guides

icmp port unreachable error message

Hello,

I am sending UDP packets from one PC to another. I am watching the the whole activity using Wire Shark. I notice that for some time there is smooth transmission of packets from one system to the other. Then suddenly ICMP packets with error 'port unreachable' starts to appear. Then they disappear for some time and there is again smooth transmission of UDP packets. Then these ICMP packets again appear with the same 'port unreachable' error. Then these ICMP packets disappear again and so on. And this continues in a periodic manner.

Please see the wire shark pic as below:
http://i.stack.imgur.com/w2oy5.png

Can anybody please shed some light that what could be the reason for it. and how to avoid it.

Hi,

Few questions for you before going further:
Do you have a name ?
Why are you using link local ip addresses ? ( are you missing a DHCP server ?)
What OS are you using ?
What application are you running on udp 7609 ?

Hello,
Thanks for the reply .

- Yes I do . I am gajj

- No I am not missing a DHCP server.

- My both pc are using windows 7.

- For clearity my set up is as follows. On first pc I have an application (I made using C#) which is sending udp
packets to the second pc on 7609 port. On second pc I open wireshark and observe what I explained in the last
post.

I was thinking this error might be becasue that the process in question was swapped out of memory and was not able to swap back in quickly enough to avoid the unreachable indication. But I am not sure how to solve it

Hi Gaji,

Check if the application crashes on the server side and then restarts (use "tasklist" command and check pid of the application before and after an episode of icmp unreachable).

Thanks a lot mate. It helped