[CentOS] force 10 megabit full duplex

Mon Apr 17 11:41:21 UTC 2006
William L. Maltby <BillsCentOS at triad.rr.com>

On Sun, 2006-04-16 at 14:42 -0700, centos at 911networks.com wrote:
> William Warren wrote:
> > 
> > William L. Maltby wrote:
> >> On Sat, 2006-04-15 at 19:41 -0500, Ryan Lum wrote:
> >>> Is the ethernet port in question connect to a switch?  Might try 
> >>> forcing the
> >>> port on the switch to 10 Mbit full duplex.  If it is on default the 
> >>> switch
> >>> will negotiate the speed.
> >>
> >> Not if it's an old 3Com 3C509. They don't negotiate. I have a few of
> >> those I use with an unmanaged switch. I was planning on someday seeing
> >> if just forcing them to full duplex would work (hoping the switch was
> >> smart enough to recognize the need: decent SMC with auto wire adjust ,
> >> etc., so I'm hopeful). I "programmed" the eproms, but the Linux drivers,
> >> in their infinate wisdom, force them back to half duplex. *sigh*.
> > 
> > this is a dell PE850 with intel gigabit nics.
> > 
> There are various scenarios with 10Mbps/full duplex:
> 1. 10/100 Hub: Not possible
> 2. Modern cheap switch [linksys/dlink...] On auto negotiate: The 
>   card will send a 5bit: 1000Full, 100full, 100half, 10full and 
> 10half and the switch will take whatever is the highest that it has.
> Why 10baseT usually because the wiring is Cat3 or poor wiring 
> [leads in the wrong slot] or the wiring is too close to 
> fluorescents with dying ballasts. 10baseT works with a twisted 
> pair [the T in 10baseT]. Today all modern switches assume that if 
> you use 10baseT is that's a twisted pair, therefore 10full is not 
> possible.

Drat. Well, good to know info!. I make my own wires. Cat 5 (solid core,
plenum) until I run out of the 1,000 feet I bought. Wired 568B (or A? I
can't remember which. I have to look at my diagrams). Anyway all 4 pair

Twice I end with alliterations. Maybe I should become a poet?

> No un-managed switch will negotiate to 10full. Never happened & 
> will not happen. When 10baseT was implemented Cat3 was standard 
> and you could not get 10full reliably. The drivers were not that 
> great either, even the 3com drivers were lousy under DOS.
> Today, the only way to get 10baseT full duplex is with a managed 
> switch [Cisco and the likes or web managed interfaces] and locked 
> on BOTH sides [the DTE and the DCE].
> BTW, 1000baseT is ONLY full duplex and you will need the wiring 
> to support the 8 leads. The wiring will have to be at least Cat5e 
> or Cat6

Well, I'm set to get what I can out of my SMC GB switch and cables (some
purchased "350" multi-strand patch cords claiming "350" MHz and/or my
hand made solid core ones). The 3Com and other old ISA based are used
only in my firewalls (IPCop) to the cable modem and to the switch.
Between my other nodes and the switch, I get good throughput.

Oh! I get download from good sites appx 600K *bytes* per second (+/- 30K
or so) on the gateway with a 100MHz AMD 5x86 (equiv. 486 in a 386
package) and 477K bytes through an old 66MHz Aptiva. So I am happy with
it all.

I do have an IBM Etherjet (Crystal Systems CX8920 based) nic than can do
full duplex. I want to get that in talking to the modem and see if I
gain. But I had to modify the driver for it during the 2.4 days to get
it to work in my setup at that time (coax) and I need to find the
default settings again to see if I can use the current unmodified
drivers in my twisted pair environment now.

Thanks for taking the time and effort. I always like to learn new stuff...
even if it is for my old stuff!

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL: <http://lists.centos.org/pipermail/centos/attachments/20060417/b86cbb9b/attachment-0005.sig>