Beating The Dead Horse Known as Gigabit Auto Negotiation

August

20th

2008

Beating The Dead Horse Known as Gigabit Auto Negotiation

If you’ve read my original post on Gigabit Autonegotiation, you already know how I feel. Today, this hit me smack dab in the face. We were on a conference call with EMC. We are about to install a very expensive EMC NAS and were going over all the settings and details.

Right there on the worksheet, it said to use hard coded Gigabit Full. I couldn’t believe my eyes. This thing cost as much as a Lexus and EMC is suppose to know their stuff. When I told them I wanted to use Gigabit Autonegotiation, they balked. I couldn’t believe what I was hearing. They said they tested and found it worked best. I call bull shit on that one. Then they had the nerve to ask what Cisco thought.

Screw what Cisco thinks, this is an IEEE Standard, IEEE 802.3ab to be exact. Then they came back and said they had seen network performance problems when using Autonegotiation because it would slow down to 100Mbps on just one of the Etherchannel links. Well of course that’s a problem, but if you hard set it, then you’ll never know you have a problem, which in itself will create a bigger problem because now you have bad data constantly streaming across your lines.

Anyway, I know I’m worked up over this, but I see this all the time and it is so frustrating to me how many people just don’t get it.

If you don’t believe me, then please read this IEEE Interpretation Request on using hard coded Full Duplex Gigabitethernet. Remember, I am talking specifically about 1000Base-T “Copper” Gigabit Ethernet configuration.

All 1000BASE-T PHYs shall provide support for Auto-Negotiation (Clause 28)
and shall be capable of operating as MASTER or SLAVE. Auto-Negotiation is performed as part of the initial set-up of the link, and allows the PHYs at each end to advertise their capabilities (speed, PHY type, half or full duplex) and to automatically select the operating mode for communication on the link.

This indicates that although operating speed is allowed to be manually selected by disabling Auto-Negotiation in Control Register 0, selecting 1000BASE-T mode of operation still requires that Auto-Negotiation be used.