SBS2003 with ISA jamming ADSL router

We have a network with a SBS2003 server that connects to an ADSL router and clients connect to the internet via ISA. My PC connects directly to the router (in case of server failure). It has been running this way for 18 months or so just fine but in the last few weeks internet access has been very slow. Any site that requires much bandwidth times out.

A repeatable website indicator is youtube (No significance to youtube except that I can get it to reliably repeat my experiments).  With the server connected to the router even my pc (which is not connected through the server) cannot view a youtube video. If I unplug the server my pc gets straight through. This is the same for many other websites.

The server is not using much bandwidth. I have noticed that if I disable the Microsoft firewall service then my pc can get through but I suspect this is just because nothing can get to the router without this running.

I have changed the ADSL router for another unit and there was no change. Our router download speed is around 25 MB/s if the server is not connected.

 I have had a suggestion that something in the server may be pinging the router continously which won't show up as bandwidth use but will keep the router busy? If so what would do this? Any other ideas?
RogerNZAsked:
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pwindellConnect With a Mentor Commented:
Millions of people world wide are using SBS with ISA in an identical setup and none of them are having this issue.

This will require analyzing to a level that is just not possible with Forum Messages on a web site.  You need to get MS Support SBS Premium & ISA on the phone.  They are the only ones going to be able to analyze this the way it needs to be.

You d realize that you "router" is just a NAT-based Firewall and is redundant?  Meaning that it is not needed?  You can throw it out and the ISA will be the "router" and it is a much higher quality Firewall Product than a simply $80 NAT device is ever going to be (in spite of it running on SBS).
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RogerNZAuthor Commented:
Got an external company in to analyze as suggested. Turned out to be a forwarding DNS entry which was delivering incorrect records(?) back to us. For reasons unknown the DNS didn't seem to try the other entries.
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pwindellCommented:
Ok, very good.
Glad it worked out for you.

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