WAN with 3 subnets

Not sure if this is the right place. Our WAN consisted of the following ranges:
10.100.120.0-10.100.120.255
10.100.121.0-10.100.121.255

this worked fine until we ran out of IP's. I have been forced to use 10.100.117 as the new subnet. Our switches/routers are all set up for the new subnet. I am giving out DHCP request to this subnet without any problems.

mask for all 3 is 255.255.254.0 - this was given by a proper network techy

But, when a PC with the new 117.x range opens a document from a file share, it can take 1-2 minutes for a 1Meg file.

pings take much longer - 128-256 ms instaead of the instant responses when on the 120/121 range

I am running a mixed Windows 2000/2003 domain with Active Directory - this is set up as a single site.

Any ideas as to where else I can look - as you can see I'm not a networky guru.

thanks

Are these ranges all in use at the one site?

With the subnet mask you described, the 10.100.120.* and 10.100.121.* addresses are all on the same subnet -- hosts can talk directly.

With the new 10.100.117.* addresses, that block is on a different subnet. To get from there to 10.12x and vice versa, all the traffic has to go through a router. Depending on the age and spec of the router, that can be crippling -- it was probably only spec'd to handle whatever WAN link you might throw at it, not 100 Mb/s or more of local traffic going in and out.

You probably need to think about renumbering that entire site. To keep with the 10.100.*.* system you'd need to find a block of four third octets together, where the third one is a multiple of four (ie 10.100.4-7.*, 10.100.8-11.*, ..., 10.100.248-251.*) and change the subnet mask to 255.255.252.0. That puts everything back on the one subnet again. If 122 and 123 are available you could use those and avoid renumbering the existing stuff, but you'd still have to touch the subnet mask everywhere and I'm guessing that 122 isn't which is why you picked 117.

I'm guessing a few things about your network there though; it's hard to be really specific without seeing a network diagram and stuff. If it's a non-trivial enterprise network they might not want you uploading that to a public site like this though. :)