VLAN disappeared from 2960

[fahadshefaulhaq]

I have Cisco 2960 48 ports switch

It has multiple Vlans, the issue is when i come to my office in the morning i see my switch is on orange light status,

When i connect to the switch using telnet, i see Vlan 120 is not showing and i can not connect any PC to the network through this switch

I have to create vlan 120 to resolve this issue.

All 48 ports are on vlan 120 and this is the only vlan where my PC 's are connected to the local notwork.

Can any 1 help me for this why my Vlan 120 is missing every morning? it's happening for last 2 days.

[Leo Laohoo]

What is the VTP mode? Server?

[fahadshefaulhaq]

Yes VTP Operating Mode : Server

FEC-Workshop-11.205-NPOE#show vtp
FEC-Workshop-11.205-NPOE#show vtp status
VTP Version capable : 1 to 3
VTP version running : 1
VTP Domain Name :
VTP Pruning Mode : Disabled
VTP Traps Generation : Disabled
Device ID : 70d3.798d.c200
Configuration last modified by 10.10.11.205 at 9-23-18 06:50:29
Local updater ID is 10.10.11.205 on interface Vl10 (lowest numbered VLAN interfa
ce found)

Feature VLAN:
--------------
VTP Operating Mode : Server
Maximum VLANs supported locally : 1005
Number of existing VLANs : 11
Configuration Revision : 10
MD5 digest : 0x37 0x2A 0x3F 0x92 0x3E 0x12 0xFB 0xF4
0x29 0x99 0xE1 0x0E 0x33 0x7B 0x3F 0x76
FEC-Workshop-11.205-NPOE#exit

Connection to host lost.

[Leo Laohoo]

Try using VTP mode OFF or Client.

[fahadshefaulhaq]

There are other switches connected to this switch. If i off or change VTP to client then will it effect other switches?

The switch was working fine is the same state, do you know why is this happening? is it happen due to broadcast from any PC? or any PC Network card having some error / issue?

[Julio E. Moisa]

Hi

Are you using the default VTP settings? by default every switch is VTP Server, I think your VTP Domain is NULL, and the MD5 is different on each switch, so it could not be a problem. 

FEC-Workshop-11.205-NPOE#show vtp status
VTP Version capable : 1 to 3
VTP version running : 1
VTP Domain Name :
VTP Pruning Mode : Disabled
VTP Traps Generation : Disabled
Device ID : 70d3.798d.c200
Configuration last modified by 10.10.11.205 at 9-23-18 06:50:29
Local updater ID is 10.10.11.205 on interface Vl10 (lowest numbered VLAN interfa
ce found)

Feature VLAN:
--------------
VTP Operating Mode : Server
Maximum VLANs supported locally : 1005
Number of existing VLANs : 11
Configuration Revision : 10
MD5 digest : 0x37 0x2A 0x3F 0x92 0x3E 0x12 0xFB 0xF4
0x29 0x99 0xE1 0x0E 0x33 0x7B 0x3F 0x76
FEC-Workshop-11.205-NPOE#exit

It could be a bug or do you have any kron or automatic task, try enabling the logs to see what happend during the day. It is not a normal behavior so it could be pointing to manual manipulation, automatic task being executing each specific time or a bug. 

Hope it is useful

:-)

[fahadshefaulhaq]

Can you please help me on this, how can i enable logging? i am a beginner,

Could you please send me procedure to enable logs? 

[Julio E. Moisa]

Hi

Sure, the commands are:

enable

configure terminal

logging on

logging buffered 15000 5

logging trap 5

logging monitor 5

Try with that and please let me know if you see something executing:

switch# show log

[fahadshefaulhaq]

Thanks for you kind help,

I have tried those commands and enabled log, bellow is the result of show log. 

Please review and help me find out the issue if you see

FEC-Workshop-11.205-NPOE#sh log
Syslog logging: enabled (0 messages dropped, 1 messages rate-limited, 0 flushes,
0 overruns, xml disabled, filtering disabled)

No Active Message Discriminator.

No Inactive Message Discriminator.

Console logging: level debugging, 440 messages logged, xml disabled,
filtering disabled
Monitor logging: level notifications, 0 messages logged, xml disabled,
filtering disabled
Buffer logging: level notifications, 3 messages logged, xml disabled,
filtering disabled
Exception Logging: size (4096 bytes)
Count and timestamp logging messages: disabled
File logging: disabled
Persistent logging: disabled

No active filter modules.

Trap logging: level notifications, 441 message lines logged
Logging Source-Interface: VRF Name:

Log Buffer (15000 bytes):

Sep 23 12:47:31.690: %SYS-5-LOG_CONFIG_CHANGE: Buffer logging: level notificatio
ns, xml disabled, filtering disabled, size (15000)
Sep 23 12:47:43.678: %SYS-5-LOG_CONFIG_CHANGE: Monitor logging: level notificati
ons, xml disabled, filtering disabled
Sep 23 12:47:47.537: %SYS-5-CONFIG_I: Configured from console by fec on vty0 (10
.10.120.240)
FEC-Workshop-11.205-NPOE#exit

[Deepak Kumar]

Hi,

This is basic logs related to you made changes in your switches. Please collect logs after some time or when issue will appear again.

Regards,

Deepak Kumar

[Julio E. Moisa]

Yes, it is ok

Now you have to wait once the event occurs again, so the switch must generate some logs and it can be analyzed to know what happened. 

Remember save the config:

enable

write memory

:-)

[fahadshefaulhaq]

Thanks for your all help

I will post log tomorrow when issue occur, it happens in the morning when we start office. 

Thanks again 

[Julio E. Moisa]

You are welcome,

Have a good day