Cisco 6509-E and 3750G-24 Copper Gig Interfaces

[taylor.gravis]

I am unable to get a 6509-E (WS-X6148A-GE-TX) connected to a 3750G-24TS via their copper gigabit interfaces to come up at 1000Mbps, the interface will come up in 100Mbps mode though.  The Cable type is Cat5e and is only 20 meters long.  I have tried forcing the speed settings, disable/enable mdix, etc..., but it will not come up, I have tried new cables, but still nothing.  Any thoughts, am I missing somthing.

[Leo Laohoo · Accepted solution]

Hmmm ... Maybe the cable is not correct.  Try TDR testing the cable.  Here's the process:

1.  Command:  test cable tdr int ;

2.  Wait for approximately 7 - 10 seconds;

3.  Command:  sh    cable tdr int

Please post the output.  If the cable is Gig-capable you'll see all four pairs.  If it's not, you'll see at least two pairs.

[taylor.gravis]

This is the test from the 6509-E to the 3750G-24.

TDR test last run on: April 21 01:27:48

Interface Speed Pair Cable length        Distance to fault   Channel Pair status

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

Gi8/48    auto  1-2  N/A                 N/A                 Pair B  Terminated

                3-6  N/A                 N/A                 Pair A  Terminated

                4-5  N/A                 N/A                 Invalid Terminated

                7-8  N/A                 4    +/- 2  m       Invalid Open

This is the test from the 3750G-24 to the 6509-E.

Interface Speed Local pair Pair length        Remote pair Pair status

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

Gi1/0/23  100M  Pair A     2    +/- 4  meters Pair B      Normal

                Pair B     2    +/- 4  meters Pair A      Normal

                Pair C     2    +/- 4  meters Pair C      Normal

                Pair D     0    +/- 4  meters Pair D      Open

[taylor.gravis]

Is there a document that will explain the definition of these results, I am not an expert, but this does not look good.

[Leo Laohoo]

Your cable test gives me alot of information.  The cable is a cross-over cable and approximately 4 metres long.  But it's rated for 100Mb only.

Swap the cable out.  Pair "D" is consistently bad.   Look at the "Pair Status" and shows Pair "D" as "OPEN".  This means it's an Open Circuit.  In lay-man's term, this pair is not "touching" anything at the far end, in your case, Pair "D" is not properly terminated.

FYI:  Don't trust the manufacturer when they say that this blah-blah-blah cable is "tested" because it's half true.  Nearly all manufacturer will test the first two pairs but they'll rarely or never test the third and fourth pair.

[taylor.gravis]

Thank you, the cables have been re-terminated and everything is working now.  The TDR test command was very useful.

[Leo Laohoo]

Thank you for the rating.  Glad to be of some kind of assistance.

By the way, I forgot to tell you that in earlier IOS, the when running the TDR "test" command can bring the link down for about two seconds.  Newer IOS like 12.2(50) will allow you to do the test command "on-line" ... except when you have a PoE on the far end.