auto negotiation

Hi Experts
We are using Sun Fire v240, NIC interface Bge01 connected to a Cisco WS-C6513 switch.

Pls see the below network configuration on Bge0 Interface and also the switch configuration.

Server Configuration: On V240 server,  Bge0 interface is configured as Full Duplex 100MBPS and Auto Negotiation turned ON

Switch Configuration: On the switch side ports its 100 MBPS Full Duplex Auto Negotiation turned ON

Let's assume if we change the server Bge0 NIC settings by disabling the autonegotation.

We need to understand, what should be an expected outcome of the above change.

will they be a data collisions?

Our understanding was that a hardcoded setting of 100 MBPS FDX prevents the NIC or the switch port from negotiating to any other setting other than
100MBPS FDX. Please let us know if this is incorrect.

Thanks & Regards,
Javeed
LVL 6
javeedabdulAsked:
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omarfaridCommented:
What ever you do on either side you also do on the other side. This will keep you setup simple and with no confusion.
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javeedabdulAuthor Commented:
Hi Omerfarid

I thought of that , but My colleague would like to find what happens if he disable to the auto negotiation on server side  and have  enable on switch side.

will it effect the traffic..
Will they be a performance issue.
how do they both  interact each other . will it work or not ..
Are there any possibility of traffic collision..

Javeed
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omarfaridCommented:
I think if you change it while the system is connected, there will be no impact, but this might cause problem when system reboots, etc.

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javeedabdulAuthor Commented:
ok i agree

1.If we say 100 MBPs/FDX and Auto turned off on the server side ....at what speed and mode will the severer communicate.

2. We can not say which one is overriding, i mean autoneg or the server speed setting?

3. In general if we set 100MPBs FDX and Autoneg enabled, server can communicate maximum of 100MBPs speed

4. We need to decide whether autoneg needs to be enabled or disabled based on the requirement. Incase if we turn off the Autoneg, then we need to
make sure on the switch Autoneg is disabled.

correct me if i am wrong

Javeed Abdul
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RowleyCommented:
Was tinkering with auto-negotiation on some bge interfaces the other day. Found that with auto-neg off on the server and enabled on the switch there was no connectivity.  That's not to say that forcing link/duplex speeds hasn't worked perfectly in the past but settings were changed for a reason, generally auto-neg is the best option.

If you need to understand, for yourselves, what the effects of a change to a running system 'in your own environment' might be then you need a test or dev environment to play with.
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Brian UtterbackPrinciple Software EngineerCommented:
For a ethernet, if auto-negotiation is turned off on one side and forced to a particular value, then that side
will use the forced value, since without auto-negotiation it doesn't know anything about the other end, regardless
of what the other side is set to.

The side that has auto-negotiation turned on will end up at 10/half, regardless of what the forced values are,
because that is what the standard says to do if you fail to establish what the other side is using because it is
not using auto-negotiation.  This is one reason why you should always use auto-neg on all ports, all the time. The standard was written assuming that the only reason not to use auto-neg is that you are using legacy hardware and can't use it.

So, as we see in this case, assuming both sides are forced to 100/full and one side is auto-neg off, you end up
with intermittent failures because of mis-matched speeds, and low data rates.

Auto-neg: Don't even think about it.
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gheistCommented:
If you disable autonegotiation on one side other end is only able to select correct speed. and goes half-duplex.
Cisco Catalysts have problems with n-way autonegotiation, sometimes solved by installing more recent IOS
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javeedabdulAuthor Commented:
Thanks for you suggestion..
Happy with the solution/comments


Thanks
Javeed
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