Quoting "Thomas M. Albright" <[EMAIL PROTECTED]>: > I'm checking my network with nmap, and i keep getting thie following > message: > [root@blood root]# nmap -sS -O 192.168.0.1 > Starting nmap V. 2.54BETA7 ( www.insecure.org/nmap/ ) > RTTVAR has grown to over 2.3 seconds, decreasing to 2.0 > what is RTTVAR?
RTTVAR stands for round-trip time variation. It's something that the TCP stack keeps track of and uses to compute the retransmission timer. Also used is SRTT, or smoothed round-trip time. These two things, and a variety of magical equations, are used by the TCP stack to figure out how long it should wait for an ACK before resending a packet. This allows the TCP stack to tune itself for a given network 'connection', and not put more burdon on a possibly already saturated network. A rather short, yet fairly detailed description can be read at http://www.ietf.org/rfc/rfc2988.txt if you REALLY want to know, but that sums it up. Most of the time, in general, the TCP stack would keep track of such alchemy itself, however, setting the RTTVAR to a lower number can hypothetically, at least, fool the TCP layer into retransmitting sooner then it might do otherwise. I'm not sure I'd take that approach myself, but.. 8-) Personally, I'd like to assume that the TCP stack was written by individuals smarter then myself, and leave the alchemy up to them.. 8-P -- Thomas Charron ***************************************************************** To unsubscribe from this list, send mail to [EMAIL PROTECTED] with the text 'unsubscribe gnhlug' in the message body. *****************************************************************
