Nmap Development mailing list archives
[PATCH] UDP --badsum fix
From: doug () hcsw org
Date: Mon, 22 Jan 2007 12:07:45 -0800
Hi nmap-dev! Small fix. I was reading the UDP RFC http://www.ietf.org/rfc/rfc768.txt and noticed the following: "If the computed checksum is zero, it is transmitted as all ones (the equivalent in one's complement arithmetic). An all zero transmitted checksum value means that the transmitter generated no checksum (for debugging or for higher level protocols that don't care)." The problem is that with --badsum if a packet ends up with a checksum of 1 Nmap's --badsum will subtract 1 from it and the packet will be sent with a checksum of 0 which actually means that UDP checksums were turned off and this packet will not technically have a bad checksum. This will only happen in, on average, 1 in 65535 packets, but why send incorrect packets when you can send correct packets? Best, Doug
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Current thread:
- [PATCH] UDP --badsum fix doug (Jan 22)
- Re: [PATCH] UDP --badsum fix Fyodor (Jan 22)
- Re: [PATCH] UDP --badsum fix Kris Katterjohn (Jan 22)
- Re: [PATCH] UDP --badsum fix Andreas Ericsson (Jan 23)
- Re: [PATCH] UDP --badsum fix Kris Katterjohn (Jan 22)
- Re: [PATCH] UDP --badsum fix Fyodor (Jan 22)