James Carlson wrote: > Steven Stallion writes: > >> Garrett D'Amore wrote: >> >>> en_xxx set the bits used in 802.3u (MII) configuration. Directly >>> setting the duplex and speed properties would be a subset of >>> functionality. (Because using the en_xxx bits, you can offer to support >>> more than a single configuration ... e.g. you could offer to support 100 >>> FDX *and* 10 FDX.) >>> >> Okay, so lets say that en_10fdx_cap and en_100hdx_cap are set; does this >> affect negotiation? Is there a heuristic for choosing the correct cap? >> > > It's a strict priority defined by 802.3 section 28.2.3.3 and Annex > 28B.3. It has to be -- otherwise, there'd be no hope of > interoperability when a pair of systems have two or more modes in > common. > > For those two, 100Mbps half-duplex has higher priority than 10Mbps > full-duplex. In general, it's speed first, then duplex. > > As for "why," this is much better than bluntly disabling > autonegotiation. With autonegotiation disabled on just one side of > the link (the common installation error case), the partner is forced > to fall back to its lowest setting (10Mbps half-duplex), and nothing > works. > > Better still, of course, is not to touch the fiddlin' bits. ;-} >
Right, see http://gdamore.blogspot.com/2008/08/why-you-dont-want-to-force-link-modes.html for my most recent rant on this particular topic. -- Garrett _______________________________________________ networking-discuss mailing list [email protected]
