Archived from groups: comp.dcom.lans.ethernet (
More info?)
One related question from my side. Suppose i have 5 computers running at
100Mbps full duplex and then I plug in another system to the network which
is only 10 Mbps capable. would Autonegotiation be performed? if yes would
all the systems come down to 10 Mbps speed?
As I believe AN is performed between two link partners then how come all the
computers would talk to the new system at 10 Mbps
"Cisco_Kid" <cisco_kid_20000@hotmail.com> wrote in message
news:cc1f2d$e8l$1@home.itg.ti.com...
>
> "Rich Seifert" <usenet-@-richseifert-dot-com.invalid> wrote in message
> news:usenet--1C18C9.07594429062004@news-central.dca.giganews.com...
> > In article <cbrtqo$rb4$1@internal.wj.com>,
> > alan@internal.wj.com (Alan Strassberg) wrote:
> >
> > > I believe the spec says if one port is hard-coded full-duplex
> > > and the other isn't, then that port negotiates half-duplex.
> > > Is this correct ? Pointers to any RFC's or proof appreciated.
> > >
> >
> > If one side of a 10/100BASE-T link is manually configured for
> > full-duplex operation (by disabling Auto-Negotiation), and the other
> > side of the link is allowed to Auto-Negotiate, the negotiating side will
> > indeed resolve to half-duplex operation. This happens because the
> > negotiating side will "parallel detect" its link partner as operating in
> > either 10 or 100BASE-T. However, there is no way to determine that a
> > device is configured for full duplex absent some advertisement
> > (typically via Auto-Negotiation). Lacking any knowledge of the
> > duplexity, the "safest" route is to assume half-duplex operation.
> >
> > This algorithm is defined in IEEE 802.3 (Clause 28).
> >
> > "Hard coding" for full-duplex can also be achieved by forcing
> > Auto-Negotiation to advertise that the device can only (or is only
> > willing to) operate in full-duplex mode (as opposed to disabling A-N
> > altogether). This is a preferable method of forcing full-duplex
> > operation, since a negotiating link partner will resolve to full-duplex
> > operation (assuming it is capable of doing so), and thus avoid the
> > duplex mismatch.
> >
> > In Gigabit Ethernet (1000BASE-T) Auto-Negotiation is not optional; i.e.,
> > it cannot be disabled as in 10/100BASE-T. One side of a Gigabit Ethernet
> > link can be forced to full-duplex operation only by forcing A-N to
> > advertise that it is only willing (or capable) of operating in
> > full-duplex mode; indeed, this is commonly done. A negotiating link
> > partner will see this advertisement and configure itself for full duplex
> > mode in response, resulting in a properly operating full-duplex link.
> >
> >
> > > The question is: what happens on a VLAN on a switch with four
> > > ports but only one is hard-coded full duplex? Would the other
> > > 3 ports be forced to half?
> > > Would any other ports on the switch on different VLANs be affected ?
> > >
> >
> > Auto-Negotiation is performed on a link-by-link basis; the link
> > configuration on one port of a switch has no effect on the configuration
> > of other ports on that same switch. Note that this has nothing to do
> > with VLANs at all; the logical memberships of the ports on a switch with
> > respect to Virtual LANs is completely unrelated to the duplex
> > configuration of the ports.
>
> Just wanted to add that ports that are configured to be in the same Fast
> Etherchannel group will act as one.
> If a speed or duplex change is made to one port in a 4-port Fast
> Etherchannel group then all ports will convert
> to the new setting. Same with a 2-port FastEtherchannel group. Also, Cisco
> has a pretty good chart showing the
> resulting speed/duplex of NIC cards and switch ports related to hard-coded
> vs. auto-negotiate settings. Here's the
> URL (see Table 1).
>
>
http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note0918
6a00800a7af0.shtml
>
> Cheers!
>
> Cisco_Kid
>
>
>
>
> >
> >
> > --
> > Rich Seifert Networks and Communications Consulting
> > 21885 Bear Creek Way
> > (408) 395-5700 Los Gatos, CA 95033
> > (408) 395-1966 FAX
> >
> > Send replies to: usenet at richseifert dot com
>
>