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Hard coded Access-Port between 3750 and Nexus 3048 will not establish.

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?

4 Replies 4

glen.grant
VIP Alumni
VIP Alumni

  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.

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.

  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.

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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