Guys one of my friend is hosting a cs 1.6 server with friend using vps , both are having they are own server .His friend is using bots and has been ranked "nr" by gt but what if he continues using bots will gametracker ban just by ip or ip+port coz Even my friend has the same ip except for port ,will even my friends ip will get a bann?

Gametracker does not de-rank for using 'bots'.
One of the most frequent causes of de-ranking is fake players.
I am not aware of any server being outright IP banned simply for using fake players.
Repeatedly being de-ranked could result in an IP:port ban however and...
The Not Ranked ('NR') status may however be, or become permanent for the IP:port combination.
Multiple abuses by from a single IP may result in an IP ban or constant 'NR' status.

There are to my knowledge quite a few 'NR' servers using fake players at the bottom of ranking lists.
Not all servers have been added by their owners, and therefore not all 'NR' servers are specifically attempting to break Gametracker ranking rules.

This link makes it all quite clear;
http://www.gametracker.com/forums/forum.php?site=1&thread=108517

so basically gametracker bans with port !!?and other servers having same ip(except port) wouldnot be harmed??

There are both IP and IP:Port bans. We cannot guarantee you would remain unaffected by other servers on your same IP. For example, if there are too many issues on the IP, the entire IP may be banned.