[CentOS] 3Com 3c940 moel only giving me 100 mb throughput to network switch

Gilbert Sebenste sebenste at weather.admin.niu.edu
Mon Nov 23 18:59:59 UTC 2009


On Mon, 23 Nov 2009, Les Mikesell wrote:

> Gilbert Sebenste wrote:
>> Hello all,
>>
>> As the subject states, I have a 3Com 3c940 Ethernet card to a 1 gb network
>> switch. The switch detects it, but it only shows that it is giving me 100
>> mb/sec throughput. That card is rated for 1 GB...is there a way to force
>> it to try to use 1 GB/sec? System-config-network isn't helping me here.
>
> Does ethtool say it is running at 1Gb?  What is the source of the data?
>  Many things can't generate much more than 100Mb, especially going too
> or from a disk.

Nope, it says at 100 mb. I wonder why? Yep, I know I can only probably go 
somewhat faster, but it would be nice. Here's ethtool's output before I
did something below...

ethtool eth0
Settings for eth0:
         Supported ports: [ TP ]
         Supported link modes:   10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Supports auto-negotiation: Yes
         Advertised link modes:  10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Advertised auto-negotiation: Yes
         Speed: 100Mb/s
         Duplex: Full
         Port: Twisted Pair
         PHYAD: 0
         Transceiver: internal
         Auto-negotiation: on
         Supports Wake-on: g
         Wake-on: d
         Current message level: 0x00000037 (55)
         Link detected: yes


But then I tried this. Typing:

ethtool --change eth0 speed 1000 duplex full autoneg on

DID work! But I wonder why it didn't pick up on that automagically.

ethtool eth0
Settings for eth0:
         Supported ports: [ TP ]
         Supported link modes:   10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Supports auto-negotiation: Yes
         Advertised link modes:  10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Advertised auto-negotiation: Yes
         Speed: 1000Mb/s
         Duplex: Full
         Port: Twisted Pair
         PHYAD: 0
         Transceiver: internal
         Auto-negotiation: on
         Supports Wake-on: g
         Wake-on: d
         Current message level: 0x00000037 (55)
         Link detected: yes

And thanks, Les, for the ethtool reminder/tip!

*******************************************************************************
Gilbert Sebenste                                                     ********
(My opinions only!)                                                  ******
Staff Meteorologist, Northern Illinois University                      ****
E-mail: sebenste at weather.admin.niu.edu                                  ***
web: http://weather.admin.niu.edu                                      **
*******************************************************************************


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