I recently maintain one NT domain.
This domain encompasses two subnets separated by a T1 connection.
My subnet masks are 255.255.255.0 on both.
I use DHCP and TCP/IP.
About 8 PCS on office A and about 30 on office B.
PDC and BDC are in office B, authentication therefore happens
in office B.
The two offices are connected through routers with a T1 line.
Use ethernet within every office.

My problem: If I want to copy files from office A to office B
it takes very long. It makes sense as the T1 represents a bottleneck.
T1 at its best is 1.5MBS so I understand.
When I try to copy a 1MB file from one PC in office B to another PC
in office B it is instantenous, I don't even get a transfer file window.

When I try to copy a file from an office A PC to another office A PC
it also takes a long time, the 1MB file takes 10 seconds. I don't understand.
Maybe I have it set up wrong. Because as I understand it when PC1 in
office A tries to send a file to PC2 in office A it theoretically should
go from PC1 to Router in Office A and rerouted to PC2 in office A. That
would be instantenous. Yet what it seems to be happening is that the packets
travel all the way to office B and back to office A.
Can I avoid this?