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chrisatclovis
Beginner

Connection issue between 2960x and 3750G, never seen this before

This is a very weird issue and I'd like to see what you all think about it.

I'm attempting to connect a 2960x 24p switch to a pair of 3750G 12p SFP switches running HSRP.  The 2960 has a fiber link (GLC-LH-SMD modules in all devices) between each switch:

2960 1/0/25 --> 3750G 1/0/11

2960 1/0/27 --> 3750G 1/0/11

Each interface is configured as a trunk with dot1q and a native vlan.  This is where it gets interesting.  After connecting the fiber, link lights on the 2960x are green and the interfaces show up/up.  CDP neighbors shows nothing.  Spanning Tree shows FWD.

On the 3750G side (both switches same output), no link light, down(not connect) and no spanning tree info.  CDP neighbors shows nothing on int 1/0/11.  

2960x running 15.0(2a)EX5

3750G running 12.2(58)SE2

The 3750G is working fine, no other issues and a number of dual homed switches connected on other interfaces.

I've never experienced one side of a link show green while the other is not connect.  I shot light over the fiber connection to visually verify that the connections are correct and they are indeed connected to the correct interfaces. 

Any Ideas on what I can check?   Thank you in advance.

18 REPLIES 18
Leo Laohoo
VIP Community Legend

On the 2960X, post the complete output to the command "sh interface trunk". 

On the 3750G (both units), the complete output to the command "sh interface G1/0/11 trunk".

2960x

Port Mode Encapsulation Status Native vlan
Gi1/0/25 on 802.1q trunking 5

Port Vlans allowed on trunk
Gi1/0/25 1-4094

Port Vlans allowed and active in management domain
Gi1/0/25 1,5,44

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/25 1,5,44

Port Mode Encapsulation Status Native vlan
Gi1/0/27 on 802.1q trunking 5

Port Vlans allowed on trunk
Gi1/0/27 1-4094

Port Vlans allowed and active in management domain
Gi1/0/27 1,5,44

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/27 1,5,44

3750G-1

Port Mode Encapsulation Status Native vlan
Gi1/0/11 on 802.1q other 5

Port Vlans allowed on trunk
Gi1/0/11 none

Port Vlans allowed and active in management domain
Gi1/0/11 none

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/11 none

3750G-2

Port Mode Encapsulation Status Native vlan
Gi1/0/11 on 802.1q other 5

Port Vlans allowed on trunk
Gi1/0/11 none

Port Vlans allowed and active in management domain
Gi1/0/11 none

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/11 none

Gi1/0/11 none

Gi1/0/11 ports are not yet trunk.  Check the configuration of the ports and see if the line "switchport trunk encap dot1q" is there or not.

Thanks for the reply. 

Here is the config for each of the 3750g

interface GigabitEthernet1/0/11
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk

Port Vlans allowed on trunk
Gi1/0/11 none

Ok, thanks for the output.  Now post the output to the command "sh vlan" of both the 3750G and the 2960X.

I dont have access to the 2960x at the moment but here is relevant output from the 3750g:

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Gi1/0/11
5 Management active
x Data active
x Voice active

...

No other vlans have ports associated.  

Ok, post the complete output to the commands: 

1.  3750G:  sh interface G1/0/11; and

2.  2960X:  sh interface  G1/0/25 & G1/0/27

3750g

GigabitEthernet1/0/11 is down, line protocol is down (notconnect)
Hardware is Gigabit Ethernet, address is 0006.f6de.518b (bia 0006.f6de.518b)
MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 1000 bits/sec, 2 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
4589118 packets input, 329241821 bytes, 0 no buffer
Received 4390816 broadcasts (4053482 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 4053482 multicast, 0 pause input
0 input packets with dribble condition detected
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 9 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

2960x

GigabitEthernet1/0/25 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 0041.d269.1999 (bia 0041.d269.1999)
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 2000 bits/sec, 2 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
6879 packets output, 520740 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

I shut down int gi 1/0/27 just for testing purposes since its an identical link.

Something is not right here.  Gi1/0/11 is "down".  

Carlos Villagran
Cisco Employee

As I understand, you do not have an impact in your network but the interface shows as notconnect?

Is the SFP you are using cisco brand? There are many issues with other third party SFPs with the 3750 not recognizing them.

Best Regards!

JC

Hi Carlos,

Let me clarify, the 2960x is in a new data cabinet which we are still setting up, no user impact at the moment but no traffic passes from the 2960x.  All other switches connected to the 3750g's are working ok.  

Yes, all 4 SFP's are Cisco branded part GLC-LH-SMD

Thanks

Excellent, ok, ok, I have seen this behavior when a Duplex or a Speed mismatch occurs and the switch does not even show a log.

Can you check if auto negotiation is configured between the links?

Does the Speed and Duplex elements are specifically configured?

Regards!

JC

I set each side to 'speed nonegotiate' but still have the same issue, the 2960 shows up up and the 3750 shows notconnect.  I was unable to statically connect the speed and duplex but a sh int displays this:

Full-duplex, 1000Mb/s, link type is force-up, media type is 1000BaseLX SFP

I also tried replacing the SFP to no avail.  Checked the compatibility table for the GLC-LH-SMD and my IOS version supports it.

Hi, l have this issue too, did you solve this problem ?