Media for Speed Mismatch?!?

Speed Mismatch?!?

I've been banging my head on this one for weeks.

Can someone help me understand why network performance between Windows

2k/xp/2k3 hosts with a gigabit interface, and those with a 100/full interface are slow so?

Now, 100/full to 100/full transfers are plenty fast. Very. And 1000 to 1000 transfers outright smoke...as gigabit should.

But, for large TCP transfers from a 1gbit host to a 100mbit host it goes very Slow...

1) No matter what NIC used. Intel, Broadcom, D-Link, 3COM....or driver version. 2) No matter what version of windows to other version of windows...or different motherboards, etc...the slowness is very predictable no matter what hardware involved. 3) No matter what type of gigabit switch....Cisco 3750, several Netgears, some managed others not. 4) No matter how the switches involved are used...host and server in same switch, slow. Host and server in different switches...linked straight...routed between them...I even tried trunks between switches together w/ link ag....always slow. Always the same. 5) No matter how many times I try different Ethernet cables...Cat5, 5e, 6...some pre-made, others made by hand. 6) No matter what TCP window sizes are set to anywhere, be it client or server side or both.

I put gbit adapters in the servers, thinking they could use them to sever files to all the workstations that have 100mbit NIC's. I mean, it was logical...a gbit server "should" be able to handle 10x the throughput to 100mbit clients, right???? Nope.

Note again that the performance problem is only one way. When I push files FROM the 100mbit hosts, to the 1gbit servers, speed is expected: fast, about 80mbit/sec. When I pull files form the 1bitg servers, to the 100mbit PC's...speed is absolutely terrible. I'm taking

5mbit/sec, if that.

Looking at the packets...I'm seeing gobs and gobs of TCP retransmit frames. It's like the switches (even the fancy Cisco one) are sending data to the PC's faster than the PC's can take it....but only when moving data from 1gbit to 100mbit. (So much for "store and forward" switching.)

Also, in addition to the TCP re-Trans frames, the Cisco switch (when I put in the patch between these hosts) is telling me I've got "late collisions" on the gbit interface during the slow transfers. WTF? The PC's are all 100/full, in auto. Everything is full duplex, so why am I seeing ANY collisions of any kind at all???

Duplex mismatch, sure, I've dealt with that nastiness before, and I think I understand how that messes things up....but I've NEVER heard of a SPEED mismatch on Ethernet. Have You?

I'm coming to the conclusion that if I want to have gbit NICs around, AND use them at that speed...I have to dedicate a totally separate fabric for them. Great...so all my servers can talk to one another at

1000...at least backups will still smoke...but they must all serve at the same speed as clients? Why did I even bother buying any gbit switches if I can't really use them?

Help? What else can I try?