Problem with autonegotiation on 3750

Unanswered Question
May 21st, 2010

Hi all-


We're experiencing weird issue with autonegotiation on two 3750 switches.


1. WS-C3750G-24TS-S, IOS 12.2(25)SEB4


One of the gigabit ports (GigabitEthernet) of the switch is configured to speed auto, duplex auto.  When I attach a server with gigabit interface (both speed and duplex set to auto) I see that the switch port was negotiated to 10/full, from the server side it's 100/full.  I don't see any CRC errors on the switch interface and the link is up.  I tried to force 1000/full on both sides but link goes down for good.  As soon as I put auto the line is up with 10/full on a switch side and 100/full on a server side.


2. WS-C3750G-24TS-S, IOS 12.2(25)SEB4


Same situation as in case 1, but this time the speed is negotiated to 100/full on both sides, although they should support 1000/full.  Again, no CRCs and forcing the speed brings interface down.


Tried to replace cables and switch ports -- no luck.  I have plenty of other servers (same hardware, same driver version) connected to this switches that work 1000/full.


Does it look like IOS bug?  Any hints would be greatly appreciated!


Thanks.

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Mohamed Sobair Fri, 05/21/2010 - 08:20

In Short,



1- You cant have one interface as 10M and 100M and to have the link up, they are taking different link speed so this is not possible.


    The negotiation allows you to both interfaces detect the right speed of the interface or if one is set manually , the other one is negotiated according to it.


    (This is also applicable if duplex is negotiated).



2-  The speed should be negotiated to 1000 not 100 if both interfaces are Gig.



Regards,

Mohamed

nov1ce333 Fri, 05/21/2010 - 08:53

Mohamed, I know how autonegotiation works.  This is the first time I see this weird behavior and this was the reason why I decided to ask for help.


This is what I see from the switch:


GigabitEthernet1/0/21 is up, line protocol is up (connected)

Full-duplex, 10Mb/s, media type is 10/100/1000BaseTX

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored


And this is what I see from the server:


%ethtool Eth1

Supported link modes: 10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 100baseT/Full
Advertised auto-negotiation: Yes
Speed: 100Mb/s
Duplex: Full
Port: Twisted Pair


There are other servers connected to the same switch which work 1000/full no problem.  I checked one of them:


%ethtool Eth1

Supported link modes: 10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
Advertised auto-negotiation: Yes
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair


As you can see the difference is in "Advertised link modes".  So my question is why I don't see advertised link modes on particular switch interface if it's configured to auto?

Leo Laohoo Sat, 05/22/2010 - 06:22

I don't have a 3750 with your IOS but have you tried to command on the interface "speed auto 100 1000"?


NOTE:  Boy that's one ollllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllld IOS.

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