Hi, I am facing a starnge problem regaridng PPP connection from Windows machine to the linux server. I am seeing lots of Incorrect TCP Checksum packets on the PPP windows client. I am connecting from the Windows 2000 machine. I am trying to connect using PPP connection and connecting to the FTP server on the Linux machine. The problem is once in a while on the client machine I see lots of packet with Incorrect TCP checksum error. Normally I receive the TCP packets properly, but suddenly it starts showing the packet with having WRONG TCP checksum. And this continues until the receive window size - and all those packets willbe shown as having WRONG TCP checksum. And then FTP Server on linux machine will start retransmission of all those lost packets - and due to what my downloading BW is going down. I read so many mails in the previous mailing list and found out that this problem is due to the VJ Compression - and if I turn of this feature in Windows machine - then everything seems to be working fine - except little bit lower downloading speed. Now this is a very strange problem. The project we are working requires the FTP DOWNLOADING TESTING with IP Compression on on the client side while connecting to the server. So I have to resolve this problem without disabling the IP Compression on Windows client machine. Alos - one INTERESTING observation I have made is - if we TURN ON the tcp_timesstamps flag in /proc/sys/net/ipv4 then everything seems to be working fine - bi=ut if we TURN OFF the flag then only this INCORRECT (BAD) TCP CHECKSUM error will show up on the client side. But somehow we have to TURN THIS OFF - as enabling it would cost some time and we dont want that. I have taken a TCP dump on the client machine and found out that - the first packet it evaluates as havin BAD CHECKSUM - has the CORRECT CHECKSUM of the folloing packets and so on unitl the whole chunk of BAD CHECKSUM finishes. I mean the checksum of the first BAD CHECKSUM PACKET is the correct checksum of the THIRD BAD CHECKSUM PACKET, checksum of 2nd if the correct checksum of 4th paqcket and so on... Now this is a kind of big trouble for us - as we have to overcome this problem and show the downloading performace without turning of the IP COMPRESSION AND WITH DISABLING THE tcp_timestamps flag. So, not the problem is whaqt can be wrong and how to deal with this issue.... Our configuration of the Linux machine is : ---------------------------------------------- RedHat 7.3 Kernel - 2.4.18-3smp initrd - 2.4.18-3smp.img 1 GB RAM Machine is running with SCSI Hardisks. Client Side -------------------- Windows 2000 Dial-up conection using Cellular phone (with IP COMPRESSION ON) - we have to turn this on only - requirement We rae using the Cellular phone as we are working on improving the perfornce over Wireless NW. Also below is the copy of the dump having this problem ---------------------------------------------------------- 10.100.5.1 - Linux FTP server 10.103.33.16 - Windows Client 18:15:41.775278 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 826177:827637(1460) ack 1 win 5840 (DF) (ttl 59, id 33654, len 1500) 18:15:41.795307 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 827637:829097(1460) ack 1 win 5840 (DF) (ttl 59, id 33655, len 1500) 18:15:41.795307 10.103.33.16.1100 > 10.100.5.1.2369: . [tcp sum ok] 1:1(0) ack 829097 win 64512 (DF) (ttl 128, id 4657, len 40) 18:15:41.805321 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 829097:830557(1460) ack 1 win 5840 (DF) (ttl 59, id 33656, len 1500) 18:15:41.805321 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 830557:832017(1460) ack 1 win 5840 (DF) (ttl 59, id 33657, len 1500) 18:15:41.805321 10.103.33.16.1100 > 10.100.5.1.2369: . [tcp sum ok] 1:1(0) ack 832017 win 64512 (DF) (ttl 128, id 4658, len 40) 18:15:42.536372 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 832017:833477(1460) ack 1 win 5840 (DF) (ttl 59, id 33658, len 1500) 18:15:42.576430 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 833477:834937(1460) ack 1 win 5840 (DF) (ttl 59, id 33659, len 1500) 18:15:42.576430 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 834937:836397(1460) ack 1 win 5840 (DF) (ttl 59, id 33660, len 1500) 18:15:42.576430 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 836397:837857(1460) ack 1 win 5840 (DF) (ttl 59, id 33661, len 1500) 18:15:42.586444 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 837857:839317(1460) ack 1 win 5840 (DF) (ttl 59, id 33662, len 1500) 18:15:42.586444 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 839317:840777(1460) ack 1 win 5840 (DF) (ttl 59, id 33663, len 1500) 18:15:42.586444 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 840777:842237(1460) ack 1 win 5840 (DF) (ttl 59, id 33664, len 1500) 18:15:42.606473 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 842237:843697(1460) ack 1 win 5840 (DF) (ttl 59, id 33665, len 1500) 18:15:42.606473 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 843697:845157(1460) ack 1 win 5840 (DF) (ttl 59, id 33666, len 1500) 18:15:42.606473 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 845157:846617(1460) ack 1 win 5840 (DF) (ttl 59, id 33667, len 1500) 18:15:42.626502 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 846617:848077(1460) ack 1 win 5840 (DF) (ttl 59, id 33668, len 1500) 18:15:42.626502 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 848077:849537(1460) ack 1 win 5840 (DF) (ttl 59, id 33669, len 1500) 18:15:42.626502 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 849537:850997(1460) ack 1 win 5840 (DF) (ttl 59, id 33670, len 1500) 18:15:42.626502 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 850997:852457(1460) ack 1 win 5840 (DF) (ttl 59, id 33671, len 1500) 18:15:42.626502 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 852457:853917(1460) ack 1 win 5840 (DF) (ttl 59, id 33672, len 1500) 18:15:42.626502 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 853917:855377(1460) ack 1 win 5840 (DF) (ttl 59, id 33673, len 1500) 18:15:42.646531 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 855377:856837(1460) ack 1 win 5840 (DF) (ttl 59, id 33674, len 1500) 18:15:42.646531 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 856837:858297(1460) ack 1 win 5840 (DF) (ttl 59, id 33675, len 1500) 18:15:42.656545 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 858297:859757(1460) ack 1 win 5840 (DF) (ttl 59, id 33676, len 1500) 18:15:42.656545 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 859757:861217(1460) ack 1 win 5840 (DF) (ttl 59, id 33677, len 1500) 18:15:42.656545 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 861217:862677(1460) ack 1 win 5840 (DF) (ttl 59, id 33678, len 1500) 18:15:42.666560 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 862677:864137(1460) ack 1 win 5840 (DF) (ttl 59, id 33679, len 1500) 18:15:42.666560 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 864137:865597(1460) ack 1 win 5840 (DF) (ttl 59, id 33680, len 1500) 18:15:42.666560 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 865597:867057(1460) ack 1 win 5840 (DF) (ttl 59, id 33681, len 1500) 18:15:42.666560 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 867057:868517(1460) ack 1 win 5840 (DF) (ttl 59, id 33682, len 1500) 18:15:42.666560 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 868517:869977(1460) ack 1 win 5840 (DF) (ttl 59, id 33683, len 1500) 18:15:42.686588 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 869977:871437(1460) ack 1 win 5840 (DF) (ttl 59, id 33684, len 1500) 18:15:42.686588 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 871437:872897(1460) ack 1 win 5840 (DF) (ttl 59, id 33685, len 1500) 18:15:42.686588 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 872897:874357(1460) ack 1 win 5840 (DF) (ttl 59, id 33686, len 1500) 18:15:42.706617 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 874357:875817(1460) ack 1 win 5840 (DF) (ttl 59, id 33687, len 1500) 18:15:42.706617 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 875817:877277(1460) ack 1 win 5840 (DF) (ttl 59, id 33688, len 1500) 18:15:42.706617 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 877277:878737(1460) ack 1 win 5840 (DF) (ttl 59, id 33689, len 1500) 18:15:42.706617 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 878737:880197(1460) ack 1 win 5840 (DF) (ttl 59, id 33690, len 1500) 18:15:42.706617 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 880197:881657(1460) ack 1 win 5840 (DF) (ttl 59, id 33691, len 1500) 18:15:42.726646 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 881657:883117(1460) ack 1 win 5840 (DF) (ttl 59, id 33692, len 1500) 18:15:42.726646 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 883117:884577(1460) ack 1 win 5840 (DF) (ttl 59, id 33693, len 1500) 18:15:42.726646 10.100.5.1.2369 > 10.103.33.16.1100: P [bad tcp cksum 680b!] 884577:885913(1336) ack 1 win 5840 (DF) (ttl 59, id 33694, len 1376) 18:15:42.726646 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 885913:887373(1460) ack 1 win 5840 (DF) (ttl 59, id 33695, len 1500) 18:15:43.617928 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 887373:888833(1460) ack 1 win 5840 (DF) (ttl 59, id 33696, len 1500) 18:15:45.480606 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 888833:890293(1460) ack 1 win 5840 (DF) (ttl 59, id 33697, len 1500) 18:15:48.364753 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 890293:891753(1460) ack 1 win 5840 (DF) (ttl 59, id 33698, len 1500) 18:15:51.359059 10.100.5.1.2369 > 10.103.33.16.1100: . [bad tcp cksum 680b!] 891753:893213(1460) ack 1 win 5840 (DF) (ttl 59, id 33699, len 1500) 18:15:54.363379 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 832017:833477(1460) ack 1 win 5840 (DF) (ttl 59, id 33702, len 1500) 18:15:54.563667 10.103.33.16.1100 > 10.100.5.1.2369: . [tcp sum ok] 1:1(0) ack 833477 win 64512 (DF) (ttl 128, id 4659, len 40) 18:15:55.084416 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 833477:834937(1460) ack 1 win 5840 (DF) (ttl 59, id 33703, len 1500) 18:15:55.094430 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 834937:836397(1460) ack 1 win 5840 (DF) (ttl 59, id 33704, len 1500) 18:15:55.094430 10.103.33.16.1100 > 10.100.5.1.2369: . [tcp sum ok] 1:1(0) ack 836397 win 64512 (DF) (ttl 128, id 4660, len 40) 18:15:55.104444 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 836397:837857(1460) ack 1 win 5840 (DF) (ttl 59, id 33705, len 1500) 18:15:55.224617 10.100.5.1.2369 > 10.103.33.16.1100: . [tcp sum ok] 837857:839317(1460) ack 1 win 5840 (DF) (ttl 59, id 33706, len 1500) Does anybody have any ide regarding this issue and what could be wrong and what could be solution for this. Tejas Vora
