Slow DNS Lookups after connecting via PPP VPN

Question

I have this very annoying problem and just can't seem to find a method to resolve it.
When I connect to my work network via a PPP VPN connection, all internet connectivity thereafter takes forever to do a DNS lookup. So when I browse the internet it takes ages before the page is displayed back.
If I also do a ping in finder for a random URL, www.google.com for example, it sits there for nearly a minute before I get a response. If I then immediately perform the ping again, I get a response straight away. So it seems once it's resolved the domain name, it gets stored in a cache somewhere. If I try another domain name, I get the same delay and then it eventually gets through.
As soon as I close the VPN connection, service is resumed and DNS lookups work fast.
I've also made sure I've unchecked the option to "Send all traffic over VPN connection".
I've also set my 'Service Order' to have my wireless Airport connection in the No #1 position.
The other thing I've tried is deleting the default route (via Terminal) and adding one manually that points to my wireless router, again without success.
Does anyone have any other ideas I could try? I've also recently re-installed a fresh copy of Leopard in case something was stuffed up, but the problem is still there after installation.
Hoping someone has an easy solution!
Many thanks

Answer 1

I seem to have found a work-around. There is probably a neater way of doing this but here goes.
Here is my setup:
Airport Wireless to my home router
PPP VPN connection to my office windows network
3G connection via mobile phone
My aim was to be able to connect to my office network via wireless at home or via my cellular data connection, but continue to route all non-work traffic via the main connection (wireless/3G).
The #1 problem I had once I connected to my office VPN on either wireless or 3G, was that DNS lookups to general internet sites took forever. So to get around this, I created TWO VPN connections to my office network in Network Preferences and in both connections I made sure the option to send all traffic over VPN was left UNCHECKED.
The first connection I then designated for use when connecting wirelessly at home. Here I manually added the IP address of my home router as a DNS entry.
The second connection I did the same by adding a new DNS entry, except here I used the DNS server of my cellular data connection, in this case T-Mobile UK.
When connecting to my office network I just use either of the above connections depending on whether I am connecting wirelessly at home or via my mobile phone.
It seems a bit long winded I grant you, but after literally months of trying to resolve this annoying problem, this appears to be the only fix that works.
The downfall of this would be that DNS resolution to any servers on your office network might not work, but that isn't a problem for me since I manually add any servers I use at work to my local hosts file. This negates any need for DNS lookups and actually speeds up access to my work servers.
In amongst this I did several reboots, so you give your machine a reboot once you've completed the above steps, just in case.
The 3G connection won't work for you if your provider changes the DNS server every time you connect, but this is unlikely.
If anyone's got any comments, I'd love to hear them.
Cheers
Phil