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Connect 2 switch cat6

theaskyme
Level 1
Level 1

I m trying to connect 2 catalyst switches as trunk using cat6  crossover cable ( around 30m )

The ports are enabled , the cable is tested and both ports set to trunk :

 

Catalyst 3650G  & Catalyst 2960

The problem is that , there is no lighting when connected. and both ports stay down.

Do you guys have any troubelshooting / solution for this ?

Thank you for your support.

28 Replies 28

Dear leolaohoo,

The following is sh cable tdr int g0/23 on 3650G switch

Interface Speed Local pair Pair length        Remote pair Pair status

--------- ----- ---------- ------------------ ----------- --------------------

Gi0/23    auto  Pair A     22   +/- 4  meters N/A         Open               

                Pair B     24   +/- 4  meters N/A         Open               

                Pair C     23   +/- 4  meters N/A         Open               

                Pair D     24   +/- 4  meters N/A         Open       

and The following is sh cable tdr int g0/1 on 2960 switch

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/1     auto  Pair A     228  +/- 2  meters N/A         Open               
                Pair B     4    +/- 2  meters N/A         Open               
                Pair C     4    +/- 2  meters N/A         Open               
                Pair D     4    +/- 2  meters N/A         Open        

Thank you for your help.

"OPEN"?  It means that you have an open circuit at the far end.  Nothing is connected.

But I m sure that the cat6 cable is connected between those 2 switches

I'd verify them again.

Firstly, the TDR is showing that you have an "OPEN" circuit.   The 3560 has a far length but the 2960 is showing the failure to be nearby.

Next you're initial post that the link lights are dark.

I'll have to consider that you have a faulty cable.

Forgot one things:

Interface Speed Local pair Pair length        Remote pair Pair status

--------- ----- ---------- ------------------ ----------- --------------------

Gi0/1     auto  Pair A     228  +/- 2  meters N/A         Open

                Pair B     4    +/- 2  meters N/A         Open

                Pair C     4    +/- 2  meters N/A         Open

                Pair D     4    +/- 2  meters N/A         Open  

That's a funny result.

Hey leolaohoo,

Thank you for your help i double check and this is the correct result :

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/1     auto  Pair A     N/A                N/A         Normal             
                Pair B     4    +/- 2  meters N/A         Open               
                Pair C     4    +/- 2  meters N/A         Open               
                Pair D     4    +/- 2  meters N/A         Open               

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/23    1000M Pair A     22   +/- 4  meters N/A         Open               
                Pair B     152  +/- 4  meters N/A         Normal             
                Pair C     23   +/- 4  meters N/A         Fail               
                Pair D     24   +/- 4  meters N/A         Open               

What you think gave the above results ?

Thank you for your help .

No offense to you but this result is getting funnier.

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/1     auto  Pair A     N/A                N/A         Normal             
                Pair B     4    +/- 2  meters N/A         Open               
                Pair C     4    +/- 2  meters N/A         Open               
                Pair D     4    +/- 2  meters N/A         Open             

Pair A is normal and the rest is an OPEN circuit.  That's not good.

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/23    1000M Pair A     22   +/- 4  meters N/A         Open               
                Pair B     152  +/- 4  meters N/A         Normal             
                Pair C     23   +/- 4  meters N/A         Fail               
                Pair D     24   +/- 4  meters N/A         Open             

Look at Pair C.  It's already "Fail"-ed.  Need I say more? Pair C controls the GigabitEthernet.  Look at the distance value of Pair "B".  It's showing 152 metres (don't take this value seriously).  But that's already bad.

I stand by my initial recommendation to investigate the cable.  You don't need cross-over because both switches are MDI/MDI-X as long as you leave the speed and duplex setting to their default value of "AUTO".

Hello leolaohoo,

I change the rj45 to rj45 for cat6 cables and now the cable is working but at 100M speed , the following is the test cable tdr on both sides :

Interface Speed Local pair Pair length        Remote pair Pair status

--------- ----- ---------- ------------------ ----------- --------------------

Gi0/23    100M  Pair A     138  +/- 4  meters Pair A      Fail               

                Pair B     153  +/- 4  meters Pair B      Normal             

                Pair C     149  +/- 4  meters Pair C      Normal             

                Pair D     0    +/- 4  meters Pair D      Fail              

Interface Speed Local pair Pair length        Remote pair Pair status

--------- ----- ---------- ------------------ ----------- --------------------

Gi0/1     100M  Pair A     N/A                Pair B      Normal             

                Pair B     N/A                Pair A      Normal             

                Pair C     N/A                Pair D      Normal             

                Pair D     N/A                Pair C      Normal            

As you notice on g0/23 there pair A fail and the pair D fail, but on the other side they are normal.

Please note that i made a staight cable and both the speed is auto.

interface GigabitEthernet0/23
switchport trunk encapsulation dot1q
switchport mode trunk
end

 

interface GigabitEthernet0/1

switchport mode trunk

end

Thank you for your help.

I change the rj45 to rj45 for cat6 cables and now the cable is working but at 100M speed ,

Ok.  Try to shut/no shut the interface and run the TDR again.  If the ethernet is UP but the speed is 100 mbps it means that one of the pairs (Pair C) is not working.  Can you elaborate what "kind" of cable are you using?  Is it out from a pack/bag or did someone use a crimper?

If this is from a pack I would recommend using a third one.  If it still doesn't work then move the connection to a different port of Gi0/23 (don't know what switch model this is) and try.

I m using a 3M cat 6 cable , around 30 meter between switches , and i use a crimper to attach the rj45 plugs.

i was using normal rj45 that i used with the cat5 cables they where not working.

when i used a different type of rj45 ( for cat6 according to the seller ) it worked but with 100 mb speed,

i will try to redo it again , and change port too.

Thank you for your replies.

mcasimirc63
Level 4
Level 4

This might be a long shot but something similar has happened to me in the past.  Can you try to wiggle the CAT6 cable to see what happens when its plugged in? CAT6's RJ45 connectors have thinner contacts than CAT5E does.  If the contacts are the issue sticking to CAT5E will work just fine.

I tried , nothing happend,

Thank you Marcus.

majed.balsharaf
Level 1
Level 1

Hi Asky Me,

   I feel you must check your mac address table.and clear the mac address table.

Switch# clear mac address table

and then make both the ports of 3560g and 2960 as default.

Switch(config)# default interface g0/23

Switch(config)# default interface g0/1

and then configure them as trunk and try.

Hi,

I too experienced a similar issue when connecting a cat 6 cable between GIGABIT switches, it doesnt seem to work, but when i connect one end to Fast Ethernet, it simply works fine.

We tried different ports, different switches, different cable but it still doesnt work when connecting 2 gig switches!!

The distance is definitely less than 90 Metres, even if it is more, how come it works between

Fast Ethernet to Gigabit switch

Gigabit to Computer

Not sure where we are going wrong?

Thanks
Victvishwa

I too experienced a similar issue when connecting a cat 6 cable between GIGABIT switches, it doesnt seem to work, but when i connect one end to Fast Ethernet, it simply works fine.

Run a TDR.

I don't know how many times I've seen this behaviour, however, I'm very certain the test will show, at least, Pair "D" as being SHORT.

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