CISCO ETHERNET NETWORK PORT

[MohdNizammuddinSaipuddin4868]

Hi, face an issue whereby when I connect a cable to the cisco switch port. it causes the whole vlan network downtime. the led blink orange once, then off. down the whole vlan network. either one I am connecting to. I have verified the same cable with other network hub and it works fine. no indication of ip address conflict.

CISCO RUNNING CONFIG

version 15.2
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Switch
!
boot-start-marker
boot-end-marker
!
enable secret 5 $1$uQP/$JzkLkcUH1PpdhFoljn3J.0
!
no aaa new-model
switch 1 provision ws-c2960xr-24ts-i
system mtu routing 1500
!
!
!
!
!
!
!
!
!
!
!
!
!
!
spanning-tree mode rapid-pvst
spanning-tree extend system-id
!
!
!
!
vlan internal allocation policy ascending
!
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0
 ip address 192.168.100.100 255.255.255.0
!
interface GigabitEthernet1/0/1
!
interface GigabitEthernet1/0/2
!
interface GigabitEthernet1/0/3
!
interface GigabitEthernet1/0/4
!
interface GigabitEthernet1/0/5
!
interface GigabitEthernet1/0/6
!
interface GigabitEthernet1/0/7
!
interface GigabitEthernet1/0/8
!
interface GigabitEthernet1/0/9
!
interface GigabitEthernet1/0/10
!
interface GigabitEthernet1/0/11
!
interface GigabitEthernet1/0/12
!
interface GigabitEthernet1/0/13
 switchport access vlan 2
 switchport mode access
!
interface GigabitEthernet1/0/14
 switchport access vlan 2
 switchport mode access
!
interface GigabitEthernet1/0/15
!
interface GigabitEthernet1/0/16
!
interface GigabitEthernet1/0/17
!
interface GigabitEthernet1/0/18
!
interface GigabitEthernet1/0/19
!
interface GigabitEthernet1/0/20
!
interface GigabitEthernet1/0/21
!
interface GigabitEthernet1/0/22
!
interface GigabitEthernet1/0/23
!
interface GigabitEthernet1/0/24
!
interface GigabitEthernet1/0/25
!
interface GigabitEthernet1/0/26
!
interface GigabitEthernet1/0/27
!
interface GigabitEthernet1/0/28
!
interface Vlan1
 no ip address
!
interface Vlan2
 no ip address
!
ip forward-protocol nd
!
ip http server
ip http secure-server
!
!
!
!
line con 0
line vty 0 4
 password cisco
 login
 transport input telnet
line vty 5 15
 password cisco
 login
 transport input telnet
!
!
end

[Cristian Matei]

Hi,

  The network stays "down" or it recovers after some seconds, cause STP needs to converge. When the cable is connected. what is the output of "Show spanning-tree VLAN x", where x is the access VLAN configured on the port? What are you connecting on that port?

Regards,

Cristian Matei.

[MohdNizammuddinSaipuddin4868]

Hi, when the cable is connected. the network brought down and did not recover. all other port on the same vlan goes orange eventhough previously healthy. unless i unplugged the cable. then it returns healthy. did not checked that command yet though. im so new to this that i hope utilizing it as simple hub works. no need to harden just yet. so basically, this cable that causing me issue is from other switches which have 49 number of devices. all the same segment. ie 192.168.0.x/24. we just want to link them together.

[LanDownUnda]

This smells like an unexpected Spanning Tree Convergence issue.

Here are some commands you can try to look at:

-Show Logging

-Show spanning tree summary

-Show spanning tree vlan x

[MohdNizammuddinSaipuddin4868]

Hi, thanks btw. im totally new to this terminology so need to explore more. i just want to use the switch as simple hub.. at least for now actually. btw, why this was not happened if i link the switches using FO. STP does not apply?

[balaji.bandi]

"face an issue whereby when I connect a cable to the cisco switch port"

its not clear on your statement, is this cable connected to another switch or device ?

what port it was connected while you having this issue ?

what you see the Logs on the device ?  is this cross cable or straight cable ?

[MohdNizammuddinSaipuddin4868]

Hi,

- yeah this cable is coming from other switches which have 49 devices on it. all on the same ip segment ie 192.168.0.x/24. btw, it puzzled me why it works with simple hub like allied telesyn fs708? i thought something to do with security port at first.

- initially all ports are on the same vlan by default. whichever available port i am connected to, it cause the whole vlan down. the above running config i shared is after i configure port 13 and 14 on another vlan for troubleshooting purposes. so it did not interrupt my other network. however issue remain the same. if i plugged it to any available port, it will cause the whole vlan of that port (other port with similar vlan id) to be brought down.

- i did not capture the logs after i add another vlan. however, the behaviour is, the vlan protocol goes down from initially up (before the cable was connected)

- here are the common port config

Name: Gi1/0/15
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: down
Administrative Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none