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-   -   new nics - lost d/l speed (https://www.linuxquestions.org/questions/linux-networking-3/new-nics-lost-d-l-speed-620646/)

slackhack 02-12-2008 02:52 PM
new nics - lost d/l speed
 
I just put two 3com 3c905b nics in my router, and everything seemed to be working fine until I moved it back to the garage.

Now I'm getting dload speeds of less than 100K/s. Lan speed is 10M/s -- (that's normal for 10/100, right? or should it be 100M/s? or does it depend on the nics in the PCs?)

The only difference between when I was getting 1000K/s and now is 1) the cables, and 2) originally eth0 was booting up in HD mode and I changed it to FD (and then back again, but no difference).

The cables I'm using now are the same ones I've always used and gotten 500K/s download (a limitation of the old 16-bit ISA nics). I tested those cards again in the permanent router location, and they still get normal speed.

When I was installing the cards and setting everything up, I used two 5 or 6 ft. cables, and the permanent ones I think are 50ft. Could there be some issue with the cable distance (50ft. out, 50ft. back)? In that case, I just wonder why the old ISA cards don't have the same problem.

here's the info from mii-tool:

Code:
root@lou:~ # mii-tool -v
eth0: 100 Mbit, full duplex, link ok
  product info: vendor 00:00:00, model 0 rev 0
  basic mode:  100 Mbit, full duplex
  basic status: link ok
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
eth1: no autonegotiation, 10baseT-HD, link ok
  product info: vendor 00:00:00, model 0 rev 0
  basic mode:  autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  link partner: 10baseT-HD
ifconfig sometimes shows some collisions, but only like 10 or 20, not sure if that's significant or not.

What else should I check?

>>>>>>edit:

Okay, I think the link wasn't established right for some reason. I reset it to FD again with the full --force= option and rebooted, and now internet d/load speed is back to around 1000K/s.

One question I have is why does eth1 say 10baseT if it's the same card as eth0? When I change it to 100baseT it says "no link" and doesn't seem to work. I guess it's supposed to be that way since it appears to be working correctly, but is it limiting me in any way? thx.

slackhack 02-12-2008 08:22 PM
now after a while the speeds are down again. I checked a "tcp/IP analyzer" at speedguide.net and it said the rwin was too low:

Code:
Default TCP Receive Window (RWIN) = 5888
RWIN Scaling (RFC1323) = 6 bits (scale factor of 12)
Unscaled TCP Receive Window = 92

Under many Linux distributions readings in the Analyzer only show the Current TCP Window.
RWIN seems to be set to a very small number. If you're on a broadband connection, consider using a larger value.
For optimum performance, consider changing RWIN to a multiple of MSS.
Other RWIN values that might work well with your current MTU/MSS:
513920 (MSS x 44 * scale factor of 8)
256960 (MSS x 44 * scale factor of 4)
128480 (MSS x 44 * scale factor of 2)
 64240 (MSS x 44)
bandwidth * delay product (Note this is not a speed test):

Your TCP Window limits you to: 236 kbps (29 KBytes/s) @ 200ms
Your TCP Window limits you to: 94 kbps (12 KBytes/s) @ 500ms
Consider increasing your RWIN value to optimize TCP/IP for broadband.
So why did it apparently change, and how can I change it to be what it should be? Could the network card that won't switch to 100baseTx be bad?

slackhack 02-13-2008 07:51 AM
hello? no one on LQ Networking knows anything about routing or network cards? :confused:


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