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New to this software, trying to diagnose issues with new isp


Hi, I'm new to trying to diagnose networking issues, but I'm having lots of trouble with skype and games disconnecting briefly. I just moved, and my apartment complex provides Comcast Xfinity. I've been running WireShark for about 20 minutes and I've already hit 18 Errors and 13 Warnings, which seems like a lot. I'm not sure where to start in diagnosing these issues, but my goal is to establish a really solid connection. Most of my errors list either Malformed Packet or Unexpected EID Prefix AFI. Can anyone help me out? If so, do you need any more information? Thanks for your time :)

asked 16 Jun '13, 17:59

legendml's gravatar image

accept rate: 0%

Assuming there's nothing sensitive or confidiential in the trace, can you start by saving the packets you captured as a file (File > Save As), and upload it ( then post the URL to the capture?

The warnings and errors you see might not actually be a problem. With default settings there are a few common false-positives that Wireshark will complain about. The malformed packet complaint may just mean that it's trying to decode it as the wrong protocol for example.

(16 Jun '13, 18:30) Quadratic

Sure, is there any way to parse these recordings? The recording I have is far too large to upload.

Here's a 2nd scan with 15 errors in under 3 minutes

(16 Jun '13, 20:44) legendml

2 Answers:


There are a lot of ICMP Destination unreachable messages in your capture ("Host unreachable", "Port Unreachable", "Communication administratively filtered"). That could be either your own (misconfigured) firewall, or a (misconfigured) firewall at the ISP that drop some UDP connections.

After you have checked your own Firewall, please contact your ISP and ask them for help.


answered 17 Jun '13, 06:31

Kurt%20Knochner's gravatar image

Kurt Knochner ♦
accept rate: 15%


Looking at your capture file, I see about 250 Kbit of uplink traffic (mostly bittorrent). I also see quite a few retransmissions. Some of the retransmissions are caused by the ACK from you back to the server not reaching the server, others seem to be caused by data segments that you send but we're not received by the remote end. It looks like your uplink is having problems.

What are the specifications of this internet connection with regards to up/down speed? And are you the only sharing the Internet connection with others in your apartment complex? You might (collectively) saturate your uplink.

answered 17 Jun '13, 07:06

SYN-bit's gravatar image

SYN-bit ♦♦
accept rate: 20%