08-08-2012 03:17 AM - edited 03-07-2019 08:13 AM
Hello,
I have a trunk from a Cisco 3750 100mb switch to a Cisco 2960G switch. The 3750 has a 1GB SFP module installed, so I should be getting 1GB throughput, but I'm only getting 100mb.
2960
interface GigabitEthernet0/23
description Trunk to 3750 2/0/48
switchport mode trunk
2960G#sh interface GigabitEthernet0/24
GigabitEthernet0/24 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is a8b1.d4f9.c898 (bia a8b1.d4f9.c898)
Description: Trunk to 3750-1 gig 1/0/1
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 100Mb/s, link type is auto, media type is 10/100/1000BaseTX
3750
interface GigabitEthernet1/0/1
description Trunk to 2960G 0/24
switchport trunk encapsulation dot1q
switchport mode trunk
3750#sh int gig 1/0/1
GigabitEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 001e.f632.0d01 (bia 001e.f632.0d01)
Description: Trunk to 2960G 0/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 100Mb/s, link type is auto, media type is 10/100/1000BaseTX SFP
I have replaced the cable which didn't help, and I also forced the speed ont he 3750 to be "speed 1000" and then the trunk went down.
Any ideas?
Solved! Go to Solution.
08-08-2012 03:25 AM
Ok, from the 2960G, please run the following commands:
1. Command: test cable tdr interface Gig0/24;
2. Wait for approximately 5 to 7 seconds;
3. Command: sh cable tdr interface Gig0/24; and
4. Please post the output to #3.
08-08-2012 04:34 AM
Pair D 0 +/- 2 meters N/A Open
Ok, a few things.
Firstly, I don't know what IOS version you are using. I am stating this now because for a 2960G you should be able to see the distance to the fault compared to the length of your cable.
Next, you see the result of Pair "D"? Did you see it's marked as "OPEN" instead of Normal? This means there's an OPEN circuit. Unfortunately for you, Pair "D" controls GigabitEthernet. This is the reason why your interface will only connect to 100 Mbps.
From the looks of your output, the cable directly connected to the 2960G is faulty.
Read more of TDR here.
08-08-2012 03:25 AM
Ok, from the 2960G, please run the following commands:
1. Command: test cable tdr interface Gig0/24;
2. Wait for approximately 5 to 7 seconds;
3. Command: sh cable tdr interface Gig0/24; and
4. Please post the output to #3.
08-08-2012 04:26 AM
Wow I didn't know these commands existed!
sh cable tdr int gig 0/24
TDR test last run on: March 20 21:28:06
Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/24 100M Pair A N/A N/A Normal
Pair B N/A N/A Normal
Pair C N/A N/A Normal
Pair D 0 +/- 2 meters N/A Open
08-08-2012 04:34 AM
Pair D 0 +/- 2 meters N/A Open
Ok, a few things.
Firstly, I don't know what IOS version you are using. I am stating this now because for a 2960G you should be able to see the distance to the fault compared to the length of your cable.
Next, you see the result of Pair "D"? Did you see it's marked as "OPEN" instead of Normal? This means there's an OPEN circuit. Unfortunately for you, Pair "D" controls GigabitEthernet. This is the reason why your interface will only connect to 100 Mbps.
From the looks of your output, the cable directly connected to the 2960G is faulty.
Read more of TDR here.
08-08-2012 04:39 AM
Hi,
Version:
WS-C2960G-24TC-L 15.0(1)SE3 C2960-LANBASEK9-M
I've already replaced the cable though, I've tried CAT 5 and CAT6.
Regards
08-08-2012 04:41 AM
I've got 2960S running this IOS version and I've come up with good readings.
I've already replaced the cable though, I've tried CAT 5 and CAT6.
What kind of cables are we talking about here? Are these the "molded" ones or the ones that are "hand-made"?
08-08-2012 05:08 AM
It was the cable! thanks, I replaced it for a 3rd time with a new cable:
Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/24 1000M Pair A 4 +/- 10 meters Pair B Normal
Pair B 4 +/- 10 meters Pair A Normal
Pair C 4 +/- 10 meters Pair D Normal
Pair D 4 +/- 10 meters Pair C Normal
Thanks
08-08-2012 05:14 AM
Good to hear it's finally working.
08-08-2012 06:07 AM
Out of interest what does turning off DTP achieve (switchport nonegotiate)?
08-08-2012 05:11 PM
Not much. It will determine if the remote end port is an access port or a dot1q trunk. I normally disable this feature.
08-04-2017 04:46 PM
Thanks, Jon.
08-08-2012 04:15 AM
Hi Andy,
when you hardcode the speed you need to hardcode the duplx settings and to disable DTP therefore i would tell that :
interface GigabitEthernet1/0/1
description Trunk to 2960G 0/24
switchport trunk encapsulation dot1q
switchport mode trunk
switchport none
speed 1000
duplex full
and
interface GigabitEthernet0/23
description Trunk to 3750 2/0/48
switchport trunk encapsulation dot1q
switchport mode trunk
switchport none
speed 1000
duplex full
this should work. After this implementation check if the CRC are increasing and if that is the case it could be cable or the SFP interface.
HTH
Alessio
08-08-2012 04:28 AM
Let me try this, why do we need to disbale the Dynamic trunking Protocol?
Thanks
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