10-23-2012 10:39 AM - last edited on 03-25-2019 04:22 PM by ciscomoderator
Cabling between the 3750 and the N3048
Ports 19 <-> 37: STRAIGHT
Ports 20 <-> 38: CROSS-OVER
LINK CONNECTED
3750 port 19 ===> 3k port 37
speed 100 speed 100
duplex full duplex full
no negotiation auto
LINK NOT CONNECTED
3750 port 19 ===> 3k port 37
speed 1000 speed 1000
duplex full duplex full
no negotiation auto
I don’t know if this is bug related or if I am missing a command but when hard-coding at 1000, the link will Not establish with neg auto turned OFF (Tested on both Cross-over and Straight-through cables)
LINK CONNECTED
3750 port 20 ===> 3k port 38
speed 1000 speed 1000
duplex full duplex full
negotiation auto
LINK NOT CONNECTED
3750 port 20 ===> 3k port 38
speed 1000 speed 1000
duplex full duplex full
no negotiation auto
The only way that hard-coded 1000 will establish connectivity is with “Negotiation Auto” enabled.
(both cables are gig capable)
Any ideas what might be causing this?
10-23-2012 11:11 AM
My guess is that you did not use a gigabit crossover and why it didn't work . Gigabit crossovers are different than say 100 meg xovers. The reason it works as auto because mdix is correcting for any cable mismatches but this can only work when the ports are set as auto and why it doesn't work when you try to hardcode. If no issue was seen just leave them as auto between switches.
10-23-2012 11:19 AM
The problem exists with both Cross and Straight.
Using a straight cable
speed 1000, duplex full, negotiation auto Link is UP.
speed 1000, duplex full, no negotiation auto Link is DOWN.
10-23-2012 11:26 AM
That is correct a straight cable will only work having the switch use mdix which only works when the port is set as auto . If you hardcode the port on a straight cable it is going to go down, this is the correct behavior.
10-23-2012 11:57 AM
I've got a Cat6 cross-over cable plugged between the two switches. With "Auto Negotiation" turned enabled the link comes up and auto establishes at 1000 FULL proving that the cross-over cable is capable of reaching 1gig speeds. If it was Auto establishing at 100 then yes it would be my mistake, however this is not the case.
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