Solutions for slow Ethernet networking under Mac OS X 10.3.x

We continue to investigate issues with Ethernet speed under Panther, particularly with problems enabling full-duplex (simultaneous bi-directional transfer).

Enabling Spanning Tree Protocol Some readers have reported that enabling the Spanning Tree Protocol option on their managed switches allows proper full- duplex transfer. One reader writes "I was informed that I had to disable the Spanning Tree Protocol on our managed switches, in order to get NetBoot to behave. Oddly enough, that also appeared to help file copying across the network."

The primary purpose of Spanning Tree Protocol is to eliminating loops in bridged networks. Loops create never-ending data paths, resulting in excessive system overhead.

In some cases, you may need to turn on the "Fast Start" option (Nortel) or "Portfast" (Cisco) option on your spanning tree. One reader writes:

"I have yet to see this problem on an managed switch, where the problem was anything other than spanning tree not having the 'Fast Start' (Nortel) or 'Portfast' (Cisco) options turned on. By default spanning tree turns off the port until a check for a network loop has been run. This causes the port to not auto-negotiate properly.

"Portfast or Fast Start enables the port and then only disables it if a loop is detected and therefore avoids the problem at a slightly increased risk of a short lived network loop...."

Meanwhile, Tom Johnson points out that there may be some negotiation problems between networking equipment from different vendors:

"Some gear just doesn't seem to negotiate well with other gear/software driver versions. Model and vendor matter (not saying one is better than another, but you will get different results based on model and vendor). In our machine room the server and network folks have for years hard set everything on both ends since that worked more often than negotiation. In the last 2 years that has begun to change - the negotiation works more and more. Indeed, there have been several cases where we ended up using auto negotiate for both speed and duplex (on both ends of the connection of course) since that worked and better than hard set duplex. Very much an area of trial and error."

UPDATE: MacFixIt reader Aaron Adams points to an Apple Knowledge Base article (#42665) which states: '"Your computer performs best when the Ethernet port to which it is connected is set to auto-negotiate. Ask your network administrator to verify this setting.

"Important: If you experience connection problems on your network, make sure your network switch is set to auto-negotiate, if possible. If a switch's port is not auto-negotiating, your computer detects the appropriate speed but defaults to half-duplex mode. If the switch's port at the other end of the link is configured for full-duplex, a large number of late events can occur on the link. If it isn't possible to set the switch to auto-negotiate, then set the switch's port to half-duplex. For more information, see the documentation that came with the Ethernet switch."

Feedback? Late-breakers@macfixit.com.

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