Experts say to keep an eye on throughput, availability when rolling out copper Gigabit Ethernet.
As higher speeds and falling prices lure some to 1000Base-T technology, users need to be wary of an old Ethernet bugbear – port autonegotiation issues.
IT professionals deploying Gigabit Ethernet switches and network interface cards (NIC) that can communicate with 10/100M bit/sec Ethernet links – a common feature called autonegotiation – should be vigilant watching for throughput drop-offs and connection failures, experts say.
Part 1: Getting down to the wire with copper Gigabit
“Autonegotiation is the source of more connectivity problems and troubleshooting issues than just about anything,” says David Newman, president of network product evaluation firm Network Test.
In the past, glitches in switch autonegotiation have prompted users to disable the feature, Newman says.
“The most surefire way to eliminate connectivity problems is to force both sides of a link to the same speeds,” he says.
Setting a port to accept only one speed is done on most switches either through a command-line interface or management software embedded in the product. Software on PC and server NICs also allows speeds to be set, overriding autonegotiation features.
The added element of 1000M bit/sec connectivity to devices that support 10/ 100M bit/sec makes things trickier, Newman says.
“There’s just more stuff to go wrong,” he says. “The problem is not the specification. The problem is more with faulty implementations of the specifications in vendors’ products.”
Autonegotiation was built into Ethernet chips in 1996 to let variously configured Ethernet devices interoperate by agreeing on the fastest commonly supported speed, along with other settings such as flow control or full- or half-duplex setting. Some say problems can arise when two LAN nodes have different autonegotiation settings or if only one is enabled to autonegotiate. More issues can arise when older gear running a proprietary technology called autosensing – which only detects speeds and not duplex or flow-control settings – is thrown into the mix.
One engineer who helped write the autonegotiation standard says problems are often the result of bad software drivers or management applications that control autonegotiation settings.
“It’s not that the [autonegotiation] mechanism isn’t trustworthy. It’s the software behind it,” says Bob Noseworthy, 10 Gigabit Ethernet Consortium manager at the University of New Hampshire’s InterOperability Lab in Durham and an author of test suites for standardized autonegotiation technology. “That’s why a lot of people turn it off.”
Noseworthy says that while turning off autonegotiation might seem like a good idea, this practice can be time-consuming. And as 10/100/1000Base-T proliferates across enterprise networks to servers and even desktops, the task of having to adjust settings on ports individually could overwhelm an IT staff.
“It’s not that that 1000Base-T can’t work without autonegotiation,” he says, “Some users might be annoyed by having to use autonegotiation . . . but life is much more of a nightmare without it.”
Noseworthy says one reason autonegotiation is useful in 1000Base-T networks is that the high-speed Ethernet introduces a new “master/slave” concept to switch ports and end nodes, such as servers and PCs. Switches must broadcast as masters while NICs on end nodes must broadcast slave messages for a 1000M bit/sec Ethernet link to run at full speed. These messages are built into the autonegotiation function in 10/100/1000Base-T chips, he says. Shutting autonegotiation off would force users to manually configure ports on switches as master and PCs and servers as slaves.
Some IT professionals familiar with Ethernet troubleshooting say autonegotiating links can be a source of trouble, but the problem is not widespread.
At manufacturing company Sierra Nevada in Sparks, Nev., 1000Base-T switches are deployed to connect servers on the network. The switches, from Cisco, support only 1000M bit/sec Ethernet, so autonegotiation is not an issue, says Craig Cuthbert, a network engineer.
“We’ve deployed the Gigabit copper on the connections between switches where we know it will be 1000M bit/sec period or on servers where 1000M bit/sec will be the connection speed no matter what,” he says.
While Gigabit to the desktop is not in the firm’s immediate plans, he says it would be nice to have switches that can efficiently connect devices from 10M bit/sec printers to Gigabit workstations.
St. John’s Hospital in Springfield, Ill., plans to install 10/100/1000M bit/sec Ethernet switches from Enterasys Networks soon to support its database and e-mail servers. James Labonte, network engineer at the hospital, says those links probably will be set manually to Gigabit-only.
“Typically what we’ll do with our servers is set the connection speed manually anyway, even with the newer-generation switches,” Labonte says. He says autonegotiation is used on 10/100M bit/sec client connections and that he has seen some issues with performance on older network gear. Nevertheless, he is not turned off about having to configure individual server links.
“It’s OK to do that if you’re dealing with a server room that has maybe 100 servers, instead of dealing with manually configuring thousands of workstations,” he says.
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