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Double Reverse DNS Strikes Again

From Nelson Carvalho on Tue, 18 Jan 2000

hello
im contacting regarding linux. i have linux box with apach and fpt and sendmail (pop3,smtp) and a dns server and dhcp server and it work fine and fast from linux machine to linux machine. now i also have this linux box connected to a few windows machines, now i try to ftp from the windows machine to the linux box and it takes at least 90 seconds for it to connect to it, once connected it is fast and good. it also does the same thing if i try using outlookexpress to check email on the linux box. it takes about 90 seconds for it to connect and send messages, just wondering if you have any suggestions on what might be happening?
the web browser for www works with no hesitation, only ftp and mail take 90 seconds or more to establish a connection.
also these computers are not connected to the internet, its a private network.

i appriciate any help u could give me
thanks.

It sounds like you don't have DNS nor /etc/hosts entries for your MS Windows clients. If you add the IP addresses and some names for those clients to one or the other of these then your problem will probably go away.

Search my back issues on the string "double reverse dns" or "double reverse lookup" for the gory details. (Hint: it has to do with TCP Wrappers and how it figures how "who" is connecting so that it can log the connection and so that it can make policy decisions according to the content in your /etc/hosts.allow and /etc/hosts.deny files).

The easiest and smartest solution is to make sure that you have proper reverse entries in your DNS zones and/or your /etc/hosts files for all of your systems.

Copyright © 2000, James T. Dennis
Published in The Linux Gazette Issue 50 February 2000

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