[CentOS] Ethernet poor performance

Robert Moskowitz rgm at htt-consult.com
Wed Jul 2 16:40:15 UTC 2008

nate wrote:
> Robert Moskowitz wrote:
>> Any Idea where I should look to fix this?
> - What version of CentOS?


> - What type of network card?

Intel the first time, DLink (Realtek) currently. Both 10/100Mb

> - What driver is it using?

How do I tell?

> - What type of device is on the other end of the network card?(Switch, hub,
>   router etc)

The card is plugged into a switch. All boxes plugged into the switch get 
similar PING results. Good with the internal (also Intel) card, 
bad/very_bad with the PCI ethernet card.

> - Can you verify that the speed and duplex settings match on both ends of
>   the connection?

The switch has its 100Mb LED on. One of the switch ports has my 
Speedstream router which is only 10Mb, so we can believe the 100Mb LED. 
This is a dumb switch (my public network, so I am not going to plug into 
one of my Procurves).
> - I assume the ping you are running is only 1 or 2(if there's a hub/switch
>   in between) hops away?

I have done it 1 hop (directly attached boxes), 2 hops, and somewhere 
out there on the net (, a great system to use as an emergency 
DNS server).

> - Any errors reported by ifconfig ? any collisions?

No and no.

eth1 Link encap:Ethernet HWaddr 00:50:BA:42:82:49
inet addr: Bcast: Mask:
inet6 addr: fe80::250:baff:fe42:8249/64 Scope:Link
RX packets:1709 errors:0 dropped:0 overruns:0 frame:0
TX packets:1033 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:535351 (522.8 KiB) TX bytes:117321 (114.5 KiB)
Interrupt:10 Base address:0xa000

ho, ho. MTU of 1500. Is this not doing MTU path discovery? But these are 
little PINGs so there should not be any frag problems (my WAN link is 
PPPoE, so you want pathMTU or have to hard config everything to 
1415bytes per the pppoe man pages).

> - Try replacing the card itself? maybe it is bad.
On my 2nd card already.

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