On Tue, 12 Aug 2003, andy law (RI) wrote: > Donald Becker wrote: > > That is a very bad solution. If you must must disable autonegotiation > > because of flawed hardware, disable the broken end and allow > > the link to use half duplex. ... > > Bottom line: Auto-negotiation works. If you turn it off because of > > broken switches, never set the port forced-full-duplex mode. > > But from reading Table 1 in the article on the cisco site, if the > problem is at the switch end, And it usually is.. > the *ONLY* way to get a 100MB connection > is to manually configure both ends. No! The transceivers on almost all boards will fall back to autosensing the link speed if autonegotiation fails. If the link speed and duplex is configured manually, autonegotiation is implicitly turned off. The link partner will assume a 100Mbps CSMA/CD ("half duplex") link if it detects a 100baseTx link beat. > Now I'm not au-fait with the reasons to choose half-duplex or > full-duplex so I could be missing the point, > but I do know that if it comes to a choice between a 10MB link, a 100MB > link with a mismatched duplex or a working 100MB link then I'll choose > the 'bad solution' of manual configuration. That is a flawed statement of the choices. The choice is between Always configuring equipment to forced 100baseTx FULL duplex (Cisco's old advice, reinforced by years of training courses) Using autonegotiation by default, and configuring the older flawed switches to forced 100baseTx half duplex A half duplex link performs within a few percent of a full duplex link for most applications. A link with mismatched will work without apparent problems when lightly loaded, but have severe, mysterious problems when the workload increases. If you follow Cisco's old advice of forced full duplex, you've just committed your installation to long-term administrative problems and expense. Every piece of equipment that is added or moved must be manually configured or verified by a knowledgeable person. (The cynical can read the last as "trained CCNE".) And increasingly you will encounter problems with equipment that cannot be manually configured. If you use autonegotiation mixed with 100baseTx half duplex, you never have to configure new or moved equipment. -- Donald Becker becker@scyld.com Scyld Computing Corporation http://www.scyld.com 914 Bay Ridge Road, Suite 220 Scyld Beowulf cluster system Annapolis MD 21403 410-990-9993