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

Les Mikesell lesmikesell at gmail.com
Mon Nov 23 19:16:33 UTC 2009


Gilbert Sebenste wrote:
> 
>>>
>>> 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

I'd expect that to mean that it was connected to a 100Mb switch port or 
a managed switch configured to force 100Mb.

> 
> 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.

But then that wouldn't have worked either.

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

Mii-tool does some of the same things but won't show/force 1000BaseT. 
Also, you can put ETHTOOL_OPTS=... in your ifcfg-eth? files if you need 
to force something odd.

-- 
   Les Mikesell
    lesmikesell at gmail.com



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