Help diagnosing a slow inter-network connection.
 

I have three different LANs setup. Let me call these networks FNET, WNET, and DNET. The network response time internal to each of these three networks is great... no problem at all.

Additionally, the connections between FNET and DNET work fine. Also, the connections between WNET and DNET are cool.

Now the problem: The connection between FNET and WNET is slow - in one direction. If I ping one box in WNET from FNET some packets are lost. File transfers between servers on these two networks are very slow (in the indicated direction) as well. However, neither ifconfig nor netstat report any errors, overflows, or drops.

I'll draw this out:



FNET ---- slow ---> WNET
FNET <--- fast ---- WNET
^................/
|.............../
|............./
fast........fast
|........./
|......./
V...../
DNET


More detail:

FNET actually consists of two different multi-homed servers. These servers each have 3 different NICs, one for each network. One of the boxes acts as a router to route traffic between the three networks.

There is no semantic difference between the routes configured for WNET and DNET - at least that I can see. Yet, I cannot figure out what is causing the slowness. (The entire setup is using GB ethernet - routers and NICs.)

I thought for awhile that I had a cabling problem or a hardware problem. So I installed all new cat6 cabling and still have the problem. I then considered a WNET switch problem. But file transfers between boxes within WNET work fine. I even swapped machines used as the router in the FNET network and still have the problem.

All these machines are running Redhat (kernel 2.4).

Does anyone have any diagnostic suggestions?

Additional info
 

I just discovered this information that might be helpful:

It turns out that transferring files from FNET to WNET is slow; HOWEVER, transferring files FROM WNET back to FNET is fast.

In other words, transferring files in one direction is slow but transferring them back in the other direction is fast.

This has me stumped.

Any suggestions?

see traceroute or tracepath from one host to another ...

WNET# traceroute FNET

FNET# traceroute WNET

do you have asimetric routes ?

do you use an asimetric internet connection at FNET (ADSL for example)

Thanks for the response.

No, the routes aren't asymmetric - just one hop in each direction.

The only thing I can figure is that I have a driver problem or something.