Technology moves at a frighteningly fast pace, but sometimes old habits become ingrained. Take Ethernet Auto-negotiation for example. Policies and procedures that require administrators to use hard-coded "forced" or "fixed" Ethernet speed and duplex rates still exist at the too many of companies, ISPs and data centers we work with every day.
Just minutes ago, I overheard a colleague on the phone (we're in a 'cube farm', so that is unavoidable) with a customer having a connectivity issue that is a common scenario:
Interface showing errors in netstat. /var/adm/messages shows the interface linking up at 1000FDX during boot, then messages show that same interface linking up at 100FDX. Diagnosis: mismatch caused by a startup script changing/hard setting the speed/duplex on the interface post-boot, where the switchport is set to auto-negotiate. Corrective action: remove the startup script, allow the interface to auto-neg with it's link partner (the switch).
Forcing Ethernet speed/duplex is so 1994! See the "Ethernet Auto-negotiation Best Practices" blueprint and note that "Auto-neg" provides benefits that go beyond the bootup and initial startup of the interfaces, as noted on page 2 of the blueprint:Autonegotiation on the link is exchanged when:* Link is initially connected* Device at either end of the link is powered up* Device is reset or initialized* Renegotiation request is madeGigabit ethernet requires auto-negotiation to operate properly. From the Best Practices blueprint: "although autonegotiation (Clauses 22 and 28) is optional for most variants of Ethernet and manual configuration (forced mode) is allowed, this is not the case for Gigabit copper (1000BASE-T)." Note those last 2 bullets and here's another "war story":
Customer wants a root cause for a "network fault". Seems that there was a major Cisco switch upgrade over a weekend on his network and all the Sun systems were unable to communicate on the network at the end of the upgrade period. Customer is certain this is a "major flaw" in the driver and "needs it fixed right away", since "none of the other system OS' connected to the same switch saw the problem". Diagnosis: the Cisco switch sent a reset/renegotiation request to all connected systems at the end of the upgrade, but since the customer had configured all his Sun ethernet interfaces to be forced to 100FDX, they were not configured to respond/react to the request. Corrective action: configure the systems to use auto-neg. The other non-Sun systems that were unaffected were already using auto-neg.
Here are some other references on this topic:
"Configuring and Troubleshooting Ethernet 10/100/1000Mb Half/Full Duplex Auto-Negotiation" from Cisco:
"One of the most common causes of performance issues on 10/100 Mb Ethernet links occurs when one port on the link operates at half-duplex while the other port operates at full-duplex. This occurs when one or both ports on a link are reset and the auto-negotiation process does not result in both link partners having the same configuration. It also can occur when users reconfigure one side of a link and forget to reconfigure the other side. Both sides of a link should have auto-negotiation on, or both sides should have it off. Cisco recommends to leave auto-negotiation on for those devices compliant with 802.3u. "
"Gigabit Ethernet Auto-negotiation " from Dell.
Foundry Networks (maker of Brocade switches) statement on Auto-neg: " . .. .Many Ethernet products older than mid-year 1997 do not support auto-negotiation. These issues have created a situation where the new standard compliant products appear to be creating a problem, when in fact it is the older non-compliant hardware that cannot take advantage of this new valuable feature."
"Using Ethernet Auto-negotiation protocol to avoid slow network connectivity or application time outs" while the link to this whitepaper requires a subscription, the abstract reads: "In this white paper N-TRON discusses the details of Auto-negotiation protocol and how to properly configure Auto-negotiation settings for maximum performance of industrial Ethernet networks. "
Fast Ethernet is well matured and Gigabit Ethernet is becoming commonplace. 10Gigabit is increasing in usage. It's high time to dump forced ethernet connections and policies in the dustbin of computer networking history along with 2400 baud modems, Thicknet, IRQ jumpers on interface cards and dumb hubs.

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