Multiple DNS Connections Bogging System

I have a linux box running RedHat 6.0 which is an e-mail server for 60 Win95 PCs using Netscape Communicator as a e-mail client.  The linux box has its own gateway with a dedicated ISDN line and entries for our ISP's (ISP "A") DNS.  All of the client's server settings in Netscape contain the IP address of the linux box so that the name doesn't have to be resolved.  The clients who have internet access have a different gateway from a different ISP(ISP "B") with DNS settings for that ISP.

Most of the time the system works great, very fast and reliable.  Sometimes, however, the linux box gets very slow both sending and retrieving mail, making telnet connections etc. When this happens, if I check the active connections with netstat there are multiple udp connections to the ISP's DNS (ISP "A").  After a while (sometimes hours) the connections will close and things go back to normal.

Can anyone suggest a reason for this and a possible fix.  Any help would be appreciated.
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Setup local DNS on the Linux box. Then make sure the the linux box is using its own DNS and then for all local machines set all of the Windows boxen to use the Linux box for DNS. This will build up a LARGE rich cache of DNS information locally and much of the time you will not need to go across the ISDN line. This will result in much faster DNS and more bandwidth avalible for other purposes.

Given the version of RedHat you are using, DO NOT, I repeat DO NOT install bind (DNS) off the the RedHAt 6.0 CD-ROM. It has security problems, get a fresh new copy directly from the RedHat updates site.

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joetubalubeAuthor Commented:
Thanks for the quick response, them.  I have a couple of things that I hope you could clarify for me.  If I set the linux box to be its own DNS should I remove the address for the ISP's DNS from the linux settings?  And if I change all of the client's DNS settings to point to the linux box will heavy duty web surfing turn the box into more of a name resolver than an e-mail server or can it handle both?
No don't remove it, in the resolv.conf file add another line (it should be the first line in the lines of namserver lines "nameserver localhost". That way first the machine will use its own DNS server if that fails it will continue to use the ISP's which will keep mail moving in the event the local DNS fails (this is highly unlikely to happen though). The machine is going to use the local DNS 99.9999% of the time but can fall back if need be.

I would expect the machine can easily handle both email and DNS, however if you will give me the specs of the machine I can give you a much better answer.

Linux servers are VERY robust and efficient, as the local cache builds up the DNS will become larger and larger which will greatly reduce the traffic on your ISND line.
Fixed the -1 problem on this question.
Escrow points corrected.

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