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cable problem?

Dear all,

we have problem with the speed on a Port where we have to use justa 2pair cable for history reasons. U use the tdr test but I'm not sure if that looks OK. Do you have any ideas for me?

Port config:

interface GigabitEthernet1/0/38

switchport access vlan 76

switchport mode access

no cdp enable

no cdp tlv server-location

no cdp tlv app

spanning-tree portfast

spanning-tree bpduguard enable

Now I tried to add these command and hope that it helps. I can test it only next week when the users are back..

switchport nonegotiate

power inline never

speed 100

duplex full

storm-control broadcast level 10.00

Switch#     sh cable-diagnostics tdr interface gig 1/0/38
TDR test last run on: May 18 08:05:41

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/38  100M  Pair A     0    +/- 1  meters N/A         N/A
                Pair B     28   +/- 0  meters N/A         Normal
                Pair C     0    +/- 1  meters N/A         Open
                Pair D     0    +/- 1  meters N/A         Open

                  

regards,

Sebastian

Everyone's tags (1)
13 REPLIES
New Member

Re: cable problem?

Have you test the cable ?

For rj45 1 on 1, 2 on 2, 3 on 3 and 6 on 6.

Because he have R+ and R- and T+ and T- it' s thé polarity.

Gold

Re: cable problem?

hi,

why u set the speed 100 on a Gig ethernet? set it to auto and also have FLOW-CONTROL in mind

CheerZ

plz Rate if it helped.

Soroush.

Hope it Helps, Soroush.

cable problem?

I changed it to fixed speed to test or to hope that the performance issue was gone,,but nope..

The cable works since a few month already...We got that problem obnly after we change from the old switche 2948G-GE-TX to 2960S....sorry that I fogrott that info,

Hall of Fame Super Gold

Re: cable problem?

LOL!

Sorry.  Not laughing at you.  Laughing at the output of the TDR.

Pair "C" controls PoE.  If it's OPEN then it's not working therefore this renders the switchport command "power inline never" a moot point.

Pair "D" controls GigabitEthernet.  This is why the port will only negotiate to 100 Mbps.

Distance to both faults is "0" therefore the cable that's sticking out G1/0/38 of the 2960S is faulty.

If you want more help on the TDR, read my post on How to use Time-Domain Reflectometer (TDR).

Re: cable problem?

But my cable has only two pairs, 1,2 & 3,6.

We have very old cables here in some departments but the problem occur only after the switch change.

thanks for your infos about the functions maybe U have some more which pins are in which category a,b,c,d...

Best regards,

Sebastian Helmer

(sent by mobile)

Hall of Fame Super Gold

cable problem?

But my cable has only two pairs, 1,2 & 3,6.

Pairs 1,2 is Pair "A".  This control layer 1.

Pairs 3,4 is the layer 2.

If this is all your cable has, then there's no chance you can use PoE and/or GigabitEthernet.

The fault is connected to the port Gi 1/0/38.  Change that cable and see what happens.

Purple

cable problem?

   You need to check and see what the users pc nic is set at .  If the nic is hardcoded  to  a speed and duplex and that was set on the old switch hardcoded before you changed the switch  then if you did not check the settings port for port when you did the new switch and left it as auto then you have a speed/duplex mismatch .  Change the pc nic to auto/auto and the switchport to auto/auto and the problem will probably go away .

Hall of Fame Super Gold

cable problem?

 Change the pc nic to auto/auto and the switchport to auto/auto and the problem will probably go away .

Not necessarily true.  And I don't know why.  Let me explain:

In ideal situation if the NIC is triple speed (10/100/1000BaseTx), the switch will negotiate to 1 Gbps.

Now throw in a faulty cable with Pair "D" not working and guess what the switch will do?  The link will go DOWN/DOWN.  It won't negotiate to 100 or 10 Mbps.  It'll stay down until you issue the interface command "speed auto 10 100".

Found out the hard way.  Initially we thought there was an IOS bug until we did a TDR and went, "Hmmm ... Let's do something stupid and set the interface to 10/100." 

Green

cable problem?

Hi,

Could it be that as Sebastian is saying his cabling is old.

Is it CAT 3 cabling, then 10M will be the limit on Ethernet.

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.
Hall of Fame Super Gold

cable problem?

Is it CAT 3 cabling, then 10M will be the limit on Ethernet.

*GROAN*

Re: cable problem?

We use the type 1 IBM cables :(.

I tried already auto or fixed on both sites. There should be another problem. I will see what happens on Monday with the changed config where I disable power negotiations and nonegotiation and use broadcast storm control.

Or any one of U have another idea...would be cool because I have no one I just know we change the switch but take care or the speed and duplex setting.

Best regards,

Sebastian Helmer

(sent by mobile)

Hall of Fame Super Gold

cable problem?

We use the type 1 IBM cables :(.

Nope.  You are stuck with 10/100 Mbps.  You can't go higher than that unless you want to recable the entire floor.

Green

cable problem?

Hi,

From what I remember IBM type 1 was OK for token ring up to 16M

I think it can only cope with 16MHz so I think NOT to 100M

You are stuck with 10M

Also I am sure that to run 1G you need all 8 wires (4 Pairs) not 4-Wire (2-pair) as you have here.

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.
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