I recently upgraded 3 of my 5 servers to 7.0. Two of them are on
new hardware and one is on hardware that used to run 6.2. Since
then, 2 of my thousands of users are unable to access the servers
running 7.0. They can access the server running 6.2 just fine.
What happens is the server receives the SYN packet from the client
properly and then responds with the SYN packet. Nothing more is
heard from the client. The server sends a few duplicates of the SYN
and then drops the connection.
At this point I am not able to verify that the client receives the
SYN. Neither of them has a clue about tcpdump. The packets look
fine on this end (included later). Both are using Windows,
including XP and Vista. I suspect they are receiving it and not
accepting it for some reason. However, I don't really see anything
that would cause that behavior in the packets. I can't reproduce
the problem here. Every computer I can try works just fine.
Here is one of the packet traces:
11:59:00.630414 00:00:0c:38:6f:e1 (oui Cisco) > 00:a0:cc:3e:87:9e
(oui Unknown), ethertype IPv4 (0x0800), length 66:
cpe-76-169-78-119.socal.res.rr.com.59025 > zool.lafn.org.8000: S
2779920420:2779920420(0) win 8192 <mss 1460,nop,wscale
2,nop,nop,sackOK>
11:59:00.630634 00:a0:cc:3e:87:9e (oui Unknown) > 00:00:0c:38:6f:e1
(oui Cisco), ethertype IPv4 (0x0800), length 66: zool.lafn.org.8000
> cpe-76-169-78-119.socal.res.rr.com.59025: S
2480373222:2480373222(0) ack 2779920421 win 65535 <mss
1460,nop,wscale 3,sackOK,eol>
11:59:03.613011 00:00:0c:38:6f:e1 (oui Cisco) > 00:a0:cc:3e:87:9e
(oui Unknown), ethertype IPv4 (0x0800), length 66:
cpe-76-169-78-119.socal.res.rr.com.59025 > zool.lafn.org.8000: S
2779920420:2779920420(0) win 8192 <mss 1460,nop,wscale
2,nop,nop,sackOK>
11:59:03.613194 00:a0:cc:3e:87:9e (oui Unknown) > 00:00:0c:38:6f:e1
(oui Cisco), ethertype IPv4 (0x0800), length 66: zool.lafn.org.8000
> cpe-76-169-78-119.socal.res.rr.com.59025: S
2480373222:2480373222(0) ack 2779920421 win 65535 <mss
1460,nop,wscale 3,sackOK,eol>
Checking with the 6.2 server I see there are some differences in the
TCP options. 7.0 includes wscale 3 where 6.2 does not. Is there a
way to disable that feature using sysctl to see if thats the issue?
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