Author Topic: Incorrect analysis of ICMP packets (v3.0.8.214)  (Read 12496 times)

Offline egemen

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Re: Incorrect analysis of ICMP packets (v3.0.8.214)
« Reply #15 on: September 28, 2007, 02:58:20 PM »

I'm running Comodo in Win XP x64 with SP2. I observed an unusual behavior with respect to ICMP packets, and I'm not sure if this is a bug.

I'm using BitTorrent which causes a lot of outgoing UDP packets. Some of them are replied by an incoming ICMP packet of type 3, code 3 (Port unreachable). I have a rule which allows and logs these and blocks all other packets. They are logged as
ActionProtocolSource IPSource PortDestination IPDestination Port

Since ICMP has no ports, I assume that the shown values of source and destination port are equal to bits no. 0-15 and 16-31 of the incoming packet. These bits contain the port numbers for TCP and UDP. In ICMP, they contain type (0-7), code (8-15) and a checksum (16-31). I read somwhere that you have to divide the value by 256 if you run on an Intel platform. This would result in a type value of 3 which is perfectly right for unreachable-messages.

Besides the log entries shown above, there are some other entries like the following:
ActionProtocolSource IPSource PortDestination IPDestination Port

These are all PortUnreachable packets, too, but they are blocked. My assumption is that CFP analyzes bits 16-31 instead of bits 0-15, which would be incorrect.

Yep. It was a bug in displaying the logs. the latest beta should not behave like this. It is just about showing the logs. The firewall filtr is not related to this issue.



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