nanog mailing list archives
Re: Computer systems blamed for feeble hurricane response?
From: Valdis.Kletnieks () vt edu
Date: Tue, 13 Sep 2005 16:35:47 -0400
On Tue, 13 Sep 2005 15:50:12 EDT, Joseph S D Yao said:
Oh, and also ... please consider that some firewalls try to discern whether the connection on port 25 is from a mail server or from Telnet.
OK, I'll bite. A long time ago, I saw code that would trap the fact that many telnet binaries would send option negotiation on ports other than 21. What are they keying off now? Since the host in question gave a 'Connection Refused', it obviously made its decision based on the initial SYN packet. So what are they looking at? TCP options? initial window? other? 16:25:37.240700 IP h80ad2467.async.vt.edu.43404 > listserv.vt.edu.smtp: S 1026334142:1026334142(0) win 5840 <mss 1460,sackOK,timestamp 3672334 0,nop,wscale 2> 16:25:57.420455 IP h80ad2467.async.vt.edu.45093 > listserv.vt.edu.smtp: S 1074086420:1074086420(0) win 5840 <mss 1460,sackOK,timestamp 3677379 0,nop,wscale 2> One was a telnet connection, one was Sendmail. Damned if I can tell.. ;) Of course, a busticated firewall trying to tell the difference *would* explain why they aren't accepting mail. :)
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- Re: Computer systems blamed for feeble hurricane response?, (continued)
- Re: Computer systems blamed for feeble hurricane response? Mike Tancsa (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Joseph S D Yao (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Steven M. Bellovin (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Joseph S D Yao (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Joseph S D Yao (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Joseph S D Yao (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Steven M. Bellovin (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Joseph S D Yao (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Eric A. Hall (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? William Allen Simpson (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Valdis . Kletnieks (Sep 13)
- Message not available
- Re: Computer systems blamed for feeble hurricane response? Mike Tancsa (Sep 13)
- Re: Computer systems blamed for feeble hurricane response? Suresh Ramasubramanian (Sep 14)
- Re: Computer systems blamed for feeble hurricane response? Mike Tancsa (Sep 14)
- mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) william(at)elan.net (Sep 13)
- mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) Roy Badami (Sep 13)
- Re: mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) william(at)elan.net (Sep 13)
- Re: mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) Adam McKenna (Sep 13)
- Re: mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) Crist Clark (Sep 13)
- Re: mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) Steven M. Bellovin (Sep 13)
- Re: mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?) Dave Crocker (Sep 13)