SMTP banner timeout
Since last week I am fighthing with another host to send his SMTP banner
when connecting (MTA and telnet) from a debian box. When connecting to
port 25, it just does not send any banner nowether how long I'm waiting.
When connecting from non-debian boxes, everything runs fine.
This is, what I found out:
- No banner for debian boxes (tested different installations)
- No DNS problem (even tested their nameservers)
- No ident problem (even installed nullident to be sure, but there
seems to be no connection from their host anyway)
- No firewall problems
- When sending a SMTP command without waiting for the banner,
the hosts shows his banner and accepts the command
- The host runs plain SuSe 7.0 (well, that's what their admin say)
When comparing the tcpdumps of a successful connect from a non debian
box and unsuccessful connect from a debian box, the other host sends
one particular packet on and on but the debian box does not react:
12:54:59.892904 debian.1465 > them.smtp: S 2262479737:2262479737(0) win 16060 <mss 1460,sackOK,timestamp 103335313 0,nop,wscale 0> (DF) [tos 0x10]
12:54:59.924025 them.smtp > debian.1465: S 2951604287:2951604287(0) ack 2262479738 win 30660 <mss 1460,sackOK,timestamp 174627555 103335313,nop,wscale 0> [tos 0x60]
12:54:59.924064 debian.1465 > them.smtp: . ack 1 win 16060 <nop,nop,timestamp 103335316 174627555> (DF) [tos 0x10]
12:55:03.075899 them.smtp > debian.1465: S 2951604287:2951604287(0) ack 2262479738 win 30660 <mss 1460,sackOK,timestamp 174627872 103335313,nop,wscale 0> [tos 0x60]
12:55:09.590092 them.smtp > debian.1465: S 2951604287:2951604287(0) ack 2262479738 win 30660 <mss 1460,sackOK,timestamp 174628522 103335313,nop,wscale 0> [tos 0x60]
12:55:22.092523 them.smtp > debian.1465: S 2951604287:2951604287(0) ack 2262479738 win 30660 <mss 1460,sackOK,timestamp 174629772 103335313,nop,wscale 0> [tos 0x60]
and so on. This is for the standard debian 2.2.19 kernel. Now the same
with a redhat 7.0 box and 2.2.16 kernel:
13:00:30.296052 eth0 > redhat.1941 > them.smtp: S 2614152786:2614152786(0) win 32120 <mss 1460,sackOK,timestamp 163956531 0,nop,wscale 0> (DF) [tos 0x10]
13:00:30.345683 eth0 < them.smtp > redhat.1941: S 3358965424:3358965424(0) ack 2614152787 win 30660 <mss 1460,sackOK,timestamp 174667443 163956531,nop,wscale 0> [tos 0x60]
13:00:30.346156 eth0 > redhat.1941 > them.smtp: . 1:1(0) ack 1 win 32120 <nop,nop,timestamp 163956536 174667443> (DF) [tos 0x10]
13:00:33.607734 eth0 < them.smtp > redhat.1941: S 3358965424:3358965424(0) ack 2614152787 win 30660 <mss 1460,sackOK,timestamp 174667772 163956531,nop,wscale 0> [tos 0x60]
13:00:33.608085 eth0 > redhat.1941 > them.smtp: . 1:1(0) ack 1 win 32120 <nop,nop,timestamp 163956862 174667772> (DF) [tos 0x10]
13:00:33.656065 eth0 < them.smtp > redhat.1941: P 1:114(113) ack 1 win 31856 <nop,nop,timestamp 174667775 163956862> [tos 0x60]
13:00:33.656400 eth0 > redhat.1941 > them.smtp: . 1:1(0) ack 114 win 32120 <nop,nop,timestamp 163956867 174667775> (DF) [tos 0x10]
By the way, the redhat box masquerades one debian box and this debian box
does not receive a banner either.
Now I'm at the end of my knowledge and need some help :o) Is it a kernel
problem? Is it a library problem? Does debian has some default settings
which can cause this? What it the other host waiting for?
Thanks in advance!
jps
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