Question on half-duplex and full duplex

Question on half-duplex and full duplex

Post by Cheng Kwok Wing, Willi » Tue, 09 Jul 2002 11:40:15



Hi,

I've questions regarding half-duplex and full duplex of network cards.
What is the difference between these two modes??

How can I config it??

Is it set automatically according to the other end of the network,
i.e. NIC that you connect to ??

Thanks,
William

 
 
 

Question on half-duplex and full duplex

Post by Yuan Li » Tue, 09 Jul 2002 12:53:34



Quote:> Hi,

> I've questions regarding half-duplex and full duplex of network cards.
> What is the difference between these two modes??

Half duplex is like your FRS radio; full duplex is like your cell phone.

Quote:> How can I config it??

It used to be driver loading time only.  But other OS' have runtime tool
to configure this, I'd think that Linux should have.  Just don't see one.

Quote:> Is it set automatically according to the other end of the network,
> i.e. NIC that you connect to ??

> Thanks,
> William

Most cards attempt to auto negociate with its terminating party (not usually a NIC, but most often a hub or a switch).

Yuan Liu

 
 
 

Question on half-duplex and full duplex

Post by YAMABANA Kengo » Tue, 09 Jul 2002 14:30:30


Quote:> I've questions regarding half-duplex and full duplex of network cards.
> What is the difference between these two modes??

When full-duplex mode, collision-detection line is used for
data-transmission.
Full-duplex mode can theoretically be twice as fast as half-duplex.

Quote:> How can I config it??

If your nic driver is compiled in kernel, add parameter(s) to
/etc/lilo.conf and run lilo.
If your nic driver is linked as a module, add parameter(s) to
/etc/modules.conf.
Different nics have different parameter configs.

YAMABANA Kengou

 
 
 

Question on half-duplex and full duplex

Post by Eric P. McC » Tue, 09 Jul 2002 14:39:38



Quote:> I've questions regarding half-duplex and full duplex of network cards.
> What is the difference between these two modes??

Half-duplex means that only one side can be talking at a given time.
When both sides try talking at once, you get a collision.  Both sides
then wait a (more or less) random period of time, then try talking
again.  The wait interval increases (geometrically?) every time
there's another collision, until eventually only one side will be
talking at a particular time.

Full-duplex means that both sides can talk at once.  There are no
collisions and no fallbacks.

Quote:> How can I config it??
> Is it set automatically according to the other end of the network,

Yes.

Quote:> i.e. NIC that you connect to ??

If you're plugged into a hub, you are using half-duplex.  It is not
possible to use full-duplex on a hub, by definition.  If you're
plugged into a switch and your NIC supports full-duplex operation,
then your NIC should auto-negotiate to full-duplex (that is, it should
not require any configuration on your part unless something is
wrong).  One thing to note: there's no reason all NICs on a switch
_have_ to use full-duplex mode.

--

"Last I checked, it wasn't the power cord for the Clue Generator that
was sticking up your ass." - John Novak, rasfwrj

 
 
 

Question on half-duplex and full duplex

Post by Michael Heimin » Tue, 09 Jul 2002 15:18:35



[..]

Quote:> It used to be driver loading time only.  But other OS' have
> runtime tool
> to configure this, I'd think that Linux should have.  Just don't
> see one.

Try:
www.scyld.com

There are mii-diag/mii-tool and other diag tools, running on every
NIC/driver that is mii status register aware, enabling to set this
on the fly.

Case yours is not mii aware, you can set speed/FD/HD during module
load, try 'modinfo -p <Your_NIC_module>', you need to edit
/etc/modules.conf, (depmod -a), stop the network device, unload the
module and finally start the network device again, it should pick
the module, with the changed params now...

Good luck

Michael Heiming
--
Remove the +SIGNS case mail bounces.

 
 
 

Question on half-duplex and full duplex

Post by Joerg Morbitze » Tue, 09 Jul 2002 17:13:09



: Hi,
:
: I've questions regarding half-duplex and full duplex of network cards.
: What is the difference between these two modes??
:
: How can I config it??

With most cards you can use "mii-tool" to see/adjust the speed...

Regards, Joerg.

: Is it set automatically according to the other end of the network,
: i.e. NIC that you connect to ??
:
: Thanks,
: William
:

 
 
 

1. full-duplex / half-duplex switching, why?

i have rh 8.0 router with iptables and two nic's
eth0 is for local and eth1 for public network.

i can notice in messages something like this:
kernel: eth1: Setting half-duplex on MII #1 link partner capatibility
of 000
kernel: eth1: Setting full-duplex on MII #1 link partner capatibility
of 41e1

it happens more times per day, switching to half-duplex and then back
to full-duplex few minutes later.
why is that?

regards

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