Date: Sun, 23 Oct 2005 13:19:20 +0300 From: Giorgos Keramidas <keramida@freebsd.org> To: kamal kc <kamal_ckk@yahoo.com> Cc: freebsd <freebsd-net@freebsd.org>, freebsd <freebsd-hackers@freebsd.org> Subject: Re: in_cksum() for ip packets with multiple mbufs Message-ID: <20051023101919.GA9957@flame.pc> In-Reply-To: <20051023083015.18292.qmail@web35705.mail.mud.yahoo.com> References: <20051023083015.18292.qmail@web35705.mail.mud.yahoo.com>
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On 2005-10-23 01:30, kamal kc <kamal_ckk@yahoo.com> wrote: > i come across this unusual problem. > > i changed the ip_tos field of the struct ip and computed the checksum > by using in_cksum(). > > when the packet uses only one mbuf the computed checksum is ok but > when the packet uses more than one mbuf then the computed checksum is > wrong. Note that the IP header contains a checksum of the IP header only. A common mistake is to calculate the checksum of data too, which results in an invalid IP header checksum. > eg. pinging with payload less than 1470 bytes is ok but with payload > greater than 1480 bytes does not work. (the error being bad checksum > --that i knew by capturing network packets by ethereal) > > is it a real problem or i have made some mistake. > > i put the code before the if_output() in the ip_output() function. Show us the diff, if possible :)
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