Date: Wed, 2 Aug 2000 15:50:23 -0400 (EDT) From: Clinton Xavier Berni <xavier@cs.duke.edu> To: freebsd-net@FreeBSD.org Subject: confused about th_ack Message-ID: <Pine.GSO.4.21.0008021450010.29950-100000@mackerel.cs.duke.edu>
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Hi, I'm confused about the values for th_ack and th_seq in the tcp header. First let me provide some background. I'm working at the ip layer, not tcp. Therefore in order to obtain tcp header information I use the mtod() and mpullup() routines. If I have a tcp header and source or dest. port is 80 then I print out the following packet header information: ip_src - the source ip ip_dst - the destination ip src_port - the source port dst_port - the destination port th_ack - the ack sequence number th_seq - the sequence id ip_id - the ip fragment id ip_off - the offset of the fragment I downloaded a large text file using http. Many of the packets exhibit the same value for th_ack and th_seq (100s of packets). Is there something wrong or are there really that many duplicated packets sent and dropped? Maybe I'm misinterpreting the meaning of th_ack and th_seq? Here is an example of the packet output: SYN packet: ip_src 949027736, ip_dst 93062040, src_port 2241, dst_port 80, th_ack 0, th_seq 31122, ip_id 50254, ip_off 64 SYN packet: ip_src 93062040, ip_dst 949027736, src_port 80, dst_port 2241, th_ack 31122, th_seq 44343, ip_id 48929, ip_off 64 packet: ip_src 949027736, ip_dst 93062040, src_port 2241, dst_port 80, th_ack 44343, th_seq 31122, ip_id 50256, ip_off 64 packet: ip_src 949027736, ip_dst 93062040, src_port 2241, dst_port 80, th_ack 44343, th_seq 31122, ip_id 50261, ip_off 64 packet: ip_src 93062040, ip_dst 949027736, src_port 80, dst_port 2241, th_ack 31122, th_seq 44343, ip_id 49185, ip_off 64 packet: ip_src 93062040, ip_dst 949027736, src_port 80, dst_port 2241, th_ack 31122, th_seq 44343, ip_id 49441, ip_off 64 packet: ip_src 93062040, ip_dst 949027736, src_port 80, dst_port 2241, th_ack 31122, th_seq 44343, ip_id 49697, ip_off 64 packet: ip_src 949027736, ip_dst 93062040, src_port 2241, dst_port 80, th_ack 44343, th_seq 31122, ip_id 50355, ip_off 64 ... It goes on like this (~120 packets) with ip_id being the only field that changes. Any help or explanation would be appreciated. thanks, Xavier To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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