3750v2 to 3750v2 trunk looses data connection but link stays up.

[Michael Durham]

In my network I have two 3750v2 switches running IOS 15.0 connected via a trunk.  I was previously using a 3550 to 3750v2 trunk setup without any problems but i needed the 3550 for another project so I swapped it out with a 3750v2.

Now the connection data between the 2 switches drops in and out every few minutes and i cannot figure out why.  When the data connection is down, I ran a sh int fa1/0/1 on switch A and got the following output:

FastEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Fast Ethernet, address is 58bc.278f.3303 (bia 58bc.278f.3303)
Description: BLUE - Connects to House Switch
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 set (10 sec)
Full-duplex, 100Mb/s, media type is 10/100BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:10, 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 59000 bits/sec, 24 packets/sec
5 minute output rate 205000 bits/sec, 59 packets/sec
107951 packets input, 41846947 bytes, 0 no buffer
Received 3945 broadcasts (1770 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 1770 multicast, 0 pause input
0 input packets with dribble condition detected
188794 packets output, 81592108 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

While that connection is down, I am still able to use switch A to connect to a computer and the Internet.  Switch B was working just fine when it was connected to the 3550 and no configuration changes were made to it so I assume it is not where the problem is.

Attached are both Switch A and Switch B config files.  Switch A is using port fa1/0/3 to connect to switch B port fa2/0/24

I really need this solved tonight if you have any ideas, please let me know.

The trunk is what is dropping:

Shop#sh int trunk

Port        Mode             Encapsulation  Status        Native vlan
Fa1/0/1     on               802.1q         trunking      69
Fa1/0/2     on               802.1q         trunking      69
Fa1/0/3     on               802.1q         trunking      69

Port        Vlans allowed on trunk
Fa1/0/1     1-2,27,50,69,100,110,125,172,200
Fa1/0/2     1,69,100,200,1002-1005
Fa1/0/3     1-2,27,50,69,100,110,125,172,200

Port        Vlans allowed and active in management domain
Fa1/0/1     1-2,27,50,69,100,110,125,200
Fa1/0/2     1,69,100,200
Fa1/0/3     1-2,27,50,69,100,110,125,200

Port        Vlans in spanning tree forwarding state and not pruned
Fa1/0/1     1-2,27,50,69,100,110,125,200
Fa1/0/2     1,69,100,200
Fa1/0/3     1-2,27,50,69,100,110,125,200

Shop#sh int trunk

Port        Mode             Encapsulation  Status        Native vlan
Fa1/0/2     on               802.1q         trunking      69
Fa1/0/3     on               802.1q         trunking      69

Port        Vlans allowed on trunk
Fa1/0/2     1,69,100,200,1002-1005
Fa1/0/3     1-2,27,50,69,100,110,125,172,200

Port        Vlans allowed and active in management domain
Fa1/0/2     1,69,100,200
Fa1/0/3     1-2,27,50,69,100,110,125,200

Port        Vlans in spanning tree forwarding state and not pruned
Fa1/0/2     1,69,100,200
Fa1/0/3     1-2,27,50,69,100,110,125,200

I have a 3rd 3750v2 and configured it the same and it too has this problem.

Michael

[Michael Durham]

From switch B: House#sh int tru Port Mode Encapsulation Status Native vlan Fa2/0/7 on 802.1q trunking 100 Port Vlans allowed on trunk Fa2/0/7 1,69,100,200,1002-1005 Port Vlans allowed and active in management domain Fa2/0/7 1,69,100,200 Port Vlans in spanning tree forwarding state and not pruned Fa2/0/7 1,69,100,200 House#sh int tru Port Mode Encapsulation Status Native vlan Fa2/0/7 on 802.1q trunking 100 Fa2/0/24 on 802.1q trunking 69 Port Vlans allowed on trunk Fa2/0/7 1,69,100,200,1002-1005 Fa2/0/24 1-2,50,69,100,110,125,172,200 Port Vlans allowed and active in management domain Fa2/0/7 1,69,100,200 Fa2/0/24 1-2,50,69,100,110,125,200 Port Vlans in spanning tree forwarding state and not pruned Fa2/0/7 1,69,100,200 Fa2/0/24 none

[Mark Malone · Accepted solution]

Hi

the trunks don't match they need to be exact on allowing vlans , 27 is missing from B that's why its dropping , and if also if qos is applied on one side also should be on far side

As well never use STP port fast on a trunk link it will cause you issues whenever there is a calculation

interface FastEthernet2/0/24
 description BLUE - Connects to Shop Switch port fa0/1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 69
 switchport trunk allowed vlan 1,2,50,69,100,110,125,172,200
 switchport mode trunk
 switchport nonegotiate
 srr-queue bandwidth share 10 10 60 20
 priority-queue out
 mls qos trust cos
 auto qos voip trust
 spanning-tree portfast
!

interface FastEthernet1/0/3
 description RED - Connects to CME 2851 router port Gi0/1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 69
 switchport trunk allowed vlan 1,2,27,50,69,100,110,125,172,200
 switchport mode trunk
 switchport nonegotiate
 spanning-tree portfast

*******************************************

Correct config

interface FastEthernet2/0/24
 description BLUE - Connects to Shop Switch port fa0/1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 69
 switchport trunk allowed vlan 1,2,27,50,69,100,110,125,172,200
 switchport mode trunk
 switchport nonegotiate
 srr-queue bandwidth share 10 10 60 20
 priority-queue out
 mls qos trust cos
 auto qos voip trust
!

interface FastEthernet1/0/3
 description RED - Connects to CME 2851 router port Gi0/1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 69
 switchport trunk allowed vlan 1,2,27,50,69,100,110,125,172,200
 switchport mode trunk
 switchport nonegotiate
 spanning-tree portfast
 srr-queue bandwidth share 10 10 60 20
 priority-queue out
 mls qos trust cos
 auto qos voip trust
!

[Michael Durham]

You are correct that vlan 27 needed to be removed from switch A but you are looking at the wrong port on switch A.  Port 1/0/3 goes to the 2851 router and switch A to the router is working just fine.  

Switch A port fa1/0/1 is the port that connects to Switch B port 2/0/24 and port fa1/0/1 did also have vlan 27 listed; it now has been removed.  This port also had qos configured. 

SWITCH A

interface FastEthernet1/0/1
description BLUE - Connects to House Switch
switchport trunk encapsulation dot1q
switchport trunk native vlan 69
switchport trunk allowed vlan 1,2,50,69,100,110,125,172,200
switchport mode trunk
switchport nonegotiate
srr-queue bandwidth share 1 30 35 5
priority-queue out
mls qos trust cos
auto qos trust cos
spanning-tree portfast
!
interface FastEthernet1/0/2
description PINK - Connects to WiFi Shop port fa0
switchport trunk encapsulation dot1q
switchport trunk native vlan 69
switchport trunk allowed vlan 1,69,100,200,1002-1005
switchport mode trunk
switchport nonegotiate
spanning-tree portfast
!
interface FastEthernet1/0/3
description RED - Connects to CME 2851 router port Gi0/1
switchport trunk encapsulation dot1q
switchport trunk native vlan 69
switchport trunk allowed vlan 1,2,27,50,69,100,110,125,172,200
switchport mode trunk
switchport nonegotiate
srr-queue bandwidth share 1 30 35 5
priority-queue out
mls qos trust cos
auto qos trust cos
spanning-tree portfast

SWITCH B

!
interface FastEthernet2/0/24
description BLUE - Connects to Shop Switch port fa0/1
switchport trunk encapsulation dot1q
switchport trunk native vlan 69
switchport trunk allowed vlan 1,2,50,69,100,110,125,172,200
switchport mode trunk
switchport nonegotiate
srr-queue bandwidth share 10 10 60 20
priority-queue out
mls qos trust cos
auto qos voip trust
spanning-tree portfast
!

QOS question.

Switch A Port fa1/0/1 shows  priority-queue out is this correct?  This is the port that connects to Switch B, seems to me the flow is backwards?

IP phone ---> Switch B ---> Switch A --->  Router ---> Internet/SIP provider

[Mark Malone]

priority queue is just for your voice packets for qos shouldn't have an effect on the trunk , portfast is a problem its only for access ports takes it out of stp calculation which is an issue for trunks

did you check spanning-tree when it happens are both sides still forwarding  , does the switch show any logs

what exact ver 15 are you on

[Michael Durham]

Switch A - c3750-ipservicesk9-mz.150-1.SE.bin

Switch B - c3750-ipbasek9-mz.150-1.SE.bin

I can update switch B to ipservices and I will soon.  

removed the spanning-tree portfast from all trunk lines.

Seems to be working better since I fixed the vlan/trunk issue.

Thank you VERY much!

Michael

[Michael Durham]

I am still having issues with the connection between the two 3750v2 switches going up and down.  

Switch A remains connected to all hosts connected to it, just not the trunk to Switch B, The trunk will stay up for a few hours then briefly flap.  But, tonight it is flapping like a dogs tongue when hanging out the window doing 60 MHP.  Then is will settle down for a little while.

What debug commands should I run on each switch to try and figure out what the heck is going on?