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Date:      16 Feb 2003 23:20:13 +1100
From:      "Alastair D'Silva" <deece@newmillennium.net.au>
To:        freebsd-current@freebsd.org
Subject:   Libalias Corruption
Message-ID:  <1045398012.846.21.camel@picard>

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I've had a weird problem since installing 5-CURRENT on my gateway,
traffic originating from the gateway is fine, as is UDP from the
unregistered network behind it, however, TCP traffic from the
unregistered network is dropped.

It seems that natd/libalias is corrupting the tcp header.

The firewall works fine, and I have IPFW and divert sockets compiled
into the kernel. The same behaviour is exhibited regardless of whether I
have my own firewall rules loaded, or am using 'sh /etc/rc.firewall
open'.


Outputs below:

picard# uname -a
FreeBSD picard.dyn.newmillennium.net.au 5.0-CURRENT FreeBSD 5.0-CURRENT
#11: Sat Feb 15 17:51:58 EST 2003    
root@picard.dyn.newmillennium.net.au:/usr/obj/usr/src/sys/PICARD  i386


picard# netstat -s | grep 'bad header checksums'
Warning: sysctl(net.inet6.ip6.rip6stats): No such file or directory
	49 bad header checksums



picard# tcpdump -i rl2 host dhcp-194.nmn.cafn (FTP from windows box
behind the gateway)
23:11:55.075298 dhcp-194.nmn.cafn.1047 > ftp.beastie.tdk.net.ftp: S
2949494356:2949494356(0) win 64240 <mss 1460,nop,nop,sackOK> (DF)
23:11:58.076300 dhcp-194.nmn.cafn.1047 > ftp.beastie.tdk.net.ftp: S
2949494356:2949494356(0) win 64240 <mss 1460,nop,nop,sackOK> (DF)
23:12:04.085186 dhcp-194.nmn.cafn.1047 > ftp.beastie.tdk.net.ftp: S
2949494356:2949494356(0) win 64240 <mss 1460,nop,nop,sackOK> (DF)


picard# tcpdump -i tun0
23:11:55.075912 ppp82.act.padsl.internode.on.net.1047 >
ftp.beastie.tdk.net.ftp: S 2949494356:2949494356(0) win 64240 <mss
1460,nop,nop,sackOK> (DF)
23:11:55.699558 ftp.beastie.tdk.net.ftp >
ppp82.act.padsl.internode.on.net.1047: S 1498138710:1498138710(0) ack
2949494357 win 57344 <mss 1452> (DF)
23:11:58.076850 ppp82.act.padsl.internode.on.net.1047 >
ftp.beastie.tdk.net.ftp: S 2949494356:2949494356(0) win 64240 <mss
1460,nop,nop,sackOK> (DF)
23:11:58.652724 ftp.beastie.tdk.net.ftp >
ppp82.act.padsl.internode.on.net.1047: S 1498138710:1498138710(0) ack
2949494357 win 57344 <mss 1452> (DF)
23:11:58.653300 ftp.beastie.tdk.net.ftp >
ppp82.act.padsl.internode.on.net.1047: S 1498138710:1498138710(0) ack
2949494357 win 57344 <mss 1452> (DF)
.23:12:04.085667 ppp82.act.padsl.internode.on.net.1047 >
ftp.beastie.tdk.net.ftp: S 2949494356:2949494356(0) win 64240 <mss
1460,nop,nop,sackOK> (DF)
23:12:04.585676 ftp.beastie.tdk.net.ftp >
ppp82.act.padsl.internode.on.net.1047: S 1498138710:1498138710(0) ack
2949494357 win 57344 <mss 1452> (DF)
23:12:04.664324 ftp.beastie.tdk.net.ftp >
ppp82.act.padsl.internode.on.net.1047: S 1498138710:1498138710(0) ack
2949494357 win 57344 <mss 1452> (DF)
23:12:16.672935 ftp.beastie.tdk.net.ftp >
ppp82.act.padsl.internode.on.net.1047: S 1498138710:1498138710(0) ack
2949494357 win 57344 <mss 1452> (DF)


picard# netstat -s | grep 'bad header checksums'
	55 bad header checksums




-- 
Alastair D'Silva           mob: 0413 485 733
Networking Consultant      fax: 0413 181 661
New Millennium Networking  web: http://www.newmillennium.net.au


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