Solved: Gigabit interface can't go to 1000Mb/s

boban-petrovic · ‎05-15-2012

I have a 2960 with a following relevant config:

interface Port-channel1

switchport mode trunk

!

interface GigabitEthernet0/1

switchport mode trunk

channel-group 1 mode active

!

interface GigabitEthernet0/2

switchport mode trunk

bandwidth 1000000

channel-group 1 mode active

And stacked 3750's with relevant config:

interface Port-channel8

switchport trunk encapsulation dot1q

switchport mode trunk

!

interface GigabitEthernet1/0/24

switchport trunk encapsulation dot1q

switchport mode trunk

channel-group 8 mode active

!

interface GigabitEthernet2/0/24

switchport trunk encapsulation dot1q

switchport mode trunk

bandwidth 1000000

channel-group 8 mode active

!

Port gi0/1 is connected to gi1/0/24, and gi0/2 is connected to gi2/0/24

When I check channel groups, I see:

Group Port-channel Protocol Ports

------+-------------+-----------+-----------------------------------------------

8 Po8(SU) LACP Gi1/0/24(P) Gi2/0/24(s)

So port 2/0/24 is in suspended mode. It's the same on 2960

Details are:

3750#sh etherchannel 8 detail

Group state = L2

Ports: 2 Maxports = 16

Port-channels: 1 Max Port-channels = 16

Protocol: LACP

Minimum Links: 0

Ports in the group:

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

Port: Gi1/0/24

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

Port state = Up Mstr Assoc In-Bndl

Channel group = 8 Mode = Active Gcchange = -

Port-channel = Po8 GC = - Pseudo port-channel = Po8

Port index = 0 Load = 0x00 Protocol = LACP

Flags: S - Device is sending Slow LACPDUs F - Device is sending fast LACPDUs.

A - Device is in active mode. P - Device is in passive mode.

Local information:

LACP port Admin Oper Port Port

Port Flags State Priority Key Key Number State

Gi1/0/24 SA bndl 32768 0x8 0x8 0x119 0x3D

Partner's information:

LACP port Admin Oper Port Port

Port Flags Priority Dev ID Age key Key Number State

Gi1/0/24 SA 32768 0021.56a4.3000 5s 0x0 0x1 0x19 0x3D

Age of the port in the current state: 0d:19h:34m:40s

Port: Gi2/0/24

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

Port state = Up Cnt-bndl Suspend Not-in-Bndl

Channel group = 8 Mode = Active Gcchange = -

Port-channel = null GC = - Pseudo port-channel = Po8

Port index = 0 Load = 0x00 Protocol = LACP

Flags: S - Device is sending Slow LACPDUs F - Device is sending fast LACPDUs.

A - Device is in active mode. P - Device is in passive mode.

Local information:

LACP port Admin Oper Port Port

Port Flags State Priority Key Key Number State

Gi2/0/24 SA susp 32768 0x8 0x0 0x219 0x45

Age of the port in the current state: 0d:00h:20m:37s

Probable reason: speed of Gi2/0/24 is 100M, Gi1/0/24 is 1000M

Port-channels in the group:

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

Port-channel: Po8 (Primary Aggregator)

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

Age of the Port-channel = 0d:19h:51m:12s

Logical slot/port = 10/8 Number of ports = 1

HotStandBy port = null

Port state = Port-channel Ag-Inuse

Protocol = LACP

Port security = Disabled

Ports in the Port-channel:

Index Load Port EC state No of bits

------+------+------+------------------+-----------

0 00 Gi1/0/24 Active 0

Time since last port bundled: 0d:19h:34m:43s Gi1/0/24

3750#sh int gi2/0/24

GigabitEthernet2/0/24 is up, line protocol is down (suspended)

Hardware is Gigabit Ethernet, address is 0017.946f.0798 (bia 0017.946f.0798)

MTU 1500 bytes, BW 1000000 Kbit, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX

2960#sh int gi0/2

GigabitEthernet0/2 is up, line protocol is down (suspended)

Hardware is Gigabit Ethernet, address is 0021.56a4.301a (bia 0021.56a4.301a)

MTU 1500 bytes, BW 1000000 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

If I do "speed 1000" on 3750, gi0/2 on 2960 goes down, although gi0/2 support 1000Mb/s.

How to solve this?

Giuseppe Larosa · ‎05-15-2012

Hello Boban,

1000 Mbps operation requires a cable with all four pairs

try to change the cable between C2960:gi0/2 and C3750, first of all remove port channel configuration do shut/no shut interfaces an check if you are able to see both links running at 1000 Mbps before applying port channel configuration again

Eventually swap the cabling and check if the problem follows the cable.

Edit:

to force the speed manually you have to do it on both sides, but it is not recommended with gigabit ethernet

Hope to help

Giuseppe

View solution in original post

Giuseppe Larosa · ‎05-15-2012

Hello Boban,

1000 Mbps operation requires a cable with all four pairs

try to change the cable between C2960:gi0/2 and C3750, first of all remove port channel configuration do shut/no shut interfaces an check if you are able to see both links running at 1000 Mbps before applying port channel configuration again

Eventually swap the cabling and check if the problem follows the cable.

Edit:

to force the speed manually you have to do it on both sides, but it is not recommended with gigabit ethernet

Hope to help

Giuseppe

Leo Laohoo · ‎05-15-2012

Hello Boban,

1000 Mbps operation requires a cable with all four pairs

Nope. All you need is three. If you run the TDR, you need only A, B and D. Pair C controlls PoE and Pair D controls GigabitEthernet.

Giuseppe Larosa · ‎05-15-2012

Hello Leo,

as far as I know 802.3ab uses 4 pairs, PoE is a different matter

see

http://en.wikipedia.org/wiki/Gigabit_Ethernet

Hope to help

Giuseppe

Leo Laohoo · ‎05-15-2012

as far as I know 802.3ab uses 4 pairs, PoE is a different matter

I ain't going to debate on you with this because I know you are right. I was, however, talking about the TDR results taken from a Cisco switch.

Leo Laohoo · ‎05-15-2012

If I do "speed 1000" on 3750, gi0/2 on 2960 goes down, although gi0/2 support 1000Mb/s.

Run TDR on both switches. Here are the commands:

1. Command: test cable tdr interface ;

2. Wait for approximately 5 to 7 seconds;

3. Command: sh cable tdr interface ; and

4. Please post the output to the command.

boban-petrovic · ‎05-15-2012

3750#show cable-diagnostics tdr interface gigabitEthernet 2/0/24

TDR test last run on: May 15 11:10:27

Interface Speed Local pair Pair length Remote pair Pair status

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

Gi2/0/24 auto Pair A 2 +/- 4 meters Pair B Normal

Pair B 2 +/- 4 meters Pair A Normal

Pair C 0 +/- 4 meters Pair C Open

Pair D 0 +/- 4 meters Pair D Open

2960#sh cable-diagnostics tdr interface gi0/2

TDR test last run on: May 15 11:09:11

Interface Speed Local pair Pair length Remote pair Pair status

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

Gi0/2 100M Pair A N/A Pair A Normal

Pair B N/A Pair B Normal

Pair C 4 +/- 2 meters Pair C Open

Pair D 4 +/- 2 meters Pair D Open

Leo Laohoo · ‎05-15-2012

Giuseppe is right. The output from both switches is showing that Pair "D" is in Open Circuit. Pair "D" controls GigabitEthernet. This is why the interface will only negotiate to 100 Mbps.

Change the patch cable.

vijay.swaminathan · ‎05-15-2012

You could also issue show connect status to find out how the auto negotiation had worked and at what speed they have settled down at ... that would give us a fair idea about on which speed the both ends are operating and negotiated.

Just my 2 cents.

-Vijay

boban-petrovic · ‎05-15-2012

There is no "show connect status" command...

glen.grant · ‎05-15-2012

He meant "show interface status" .