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Re: Problems connectivity GE on Foundry BigIron to Cisco 2950T
From: Kevin Day <toasty () dragondata com>
Date: Sun, 15 Jan 2006 18:22:26 -0600

On Jan 15, 2006, at 6:02 PM, Sam Stickland wrote:

Replying to my own email..

I've found some sites that suggest it's not possible to disable auto-negotiation on 1000Base-T since other operational parameters are negotiated including selection of the master clock signal. I was aware that flow control was negotiated, but not the clock signal.

Can anyone elaborate?


802.3ab claims that you can't disable autonegotiation on 1000Base-T, but lots of vendors allow you to anyway.

In 100 and 10Base-T, autonegotiation decides speed, phy type and duplex. In 1000Base-T, you add in a master/slave clock source negotiation. If autonegotiation is working, the master/slave thing just 'works'. If autonegotiation is disabled and your gear allows you to force 1000mbps, you also need to manually set which is the master and which is the slave. If you do nothing, most PC/server NICs force themselves into "slave" mode, and most switches force themselves into "master" mode. For the most part, this is correct and will result in it working fine. If it isn't, you have to hope your gear supports being able to toggle it. For example, in the BSD drivers for some Broadcomm and SysKonnect cards, setting the "link0" flag on the device will flip it. For Intel chips, there's a define in the driver source.

Personally, I'd look at the copper GBIC first. Many vendors have had trouble with supporting them, and have been the cause for problems for me in the past. Make sure the version of the OS on your device claims to actually support copper GBICs.

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