Auto-negotiation on 1000-Base-SX

Unanswered Question
Jun 13th, 2008


This is continuation of my previous posts here.

I did a lot of research, but I have a problem finding one thing: Is auto-negotiation mandatory on 1000BaseX (i.e 1000BaseSX) interfaces? (in other words, should every 1000BaseX interface support auto-negotiation function))

I did a search through a lot of annexes of 802.3 standard (from 2004, 2005, 2006) but I can't find any sentence that actually says: Auto-negotiation function MUST be supported by every 1000BaseX

If you guys have any link to any documents that shows me autonegotiation function requirements, I would be more than thankful.



I have this problem too.
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padramas Fri, 06/13/2008 - 07:35

Hello Milos,

The 1000-Base-X SFP modules operates only 1000 Mbps and duplex options are not supported. however, to avoid auto-negotiation you can use " nonegotiate " keyword under the interfaces.

Speed and Duplex Configuration Guidelines

Excerpt from the above link

For SFP module ports, the speed and duplex CLI options change depending on the SFP module type:

-The 1000BASE-x (where -x is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support the nonegotiate keyword in the speed interface configuration command. Duplex options are not supported.




miloskv Fri, 06/13/2008 - 09:03

Hello Padmanabhan,

Thanks for your answer, but I have one more thing. When you look to the commands (config-if)#speed nonegotiate or (config-if)#no negotiate auto, you will see that Cisco says that these commands are not used for setting speed negotiation, but duplex/flow control and remote failures (whatever that be).

I tried to read IEEE 802.3 annex 2005 part 3 which has something like 50 pages about auto-negotiation function on 1000Base-X interfaces, but the thing is, I can't find (maybe I need new glasses) any keyword MUST, or REQUIRED to use.

So, basically, the thing is I can't find is autonegotiation function MANDATORY or OPTIONAL (and should GBIC/SPF manufacturers and/or OS manufacturers follow this standard and create auto-negotiate capable interfaces or not).

Thanks for your replies.




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