C2924 not responding after issuing trunking command

[Talha Abbasi]

Hello all,

I've run into an issue with this type switch, and hoping that you can provide some guidance/advice.

I've a 2611xm router connected to a C2924-XL switch ((C2900XL-C3H2S-M), Version 12.0(5)WC17)

Basically i configured the router as a RoTS with two sub interfaces setup with encapsulation dot1q as per below:

interface FastEthernet0/0

description TO MODEM

ip address <external IP and mask removed>

ip nat outside

duplex auto

speed auto

!

interface FastEthernet0/1

ip address 192.168.31.254 255.255.255.0

ip nat inside

ip tcp adjust-mss 1452

duplex auto

speed auto

!

interface FastEthernet0/1.10

encapsulation dot1q 10

ip address 192.168.10.254 255.255.255.0

ip access-group WCS_USER in

no ip redirects

ip nat inside

ip tcp adjust-mss 1452

!

interface FastEthernet0/1.20

encapsulation dot1q 20

ip address 192.168.20.254 255.255.255.0

ip access-group GUEST_USER in

no ip redirects

ip nat inside

ip tcp adjust-mss 1452

!

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

on the switch, i issued the following command on port fa0/4 (connected to router)

switchport mode trunk

and as soon as i pressed enter, the switch became unresponsive, as in, it wont return pings, or acknowledge telnet access and keeps timing out.  it does show up on the router when show cdp neighbor command is issued.

unfortunately, i cannot access the switch directly, as its a remote switch. 

pleaes note that prior to all this, the switch was working perfectly OK.

any tips are highly appreciated.

\regards

[sivaalthi85]

May I know on what port on router the switch is connected to ? On the router can you see that port is UP ?

Sent from Cisco Technical Support iPhone App

[Talha Abbasi]

Yes, sorry for missing that critical piece.

The switch is connected to router's port fa0/1 port, and

The router is connected to switch's port fa0/4

All are up and up

Router#sh ip int br

Interface                         IP-Address             OK?   Method    Status               Protocol

FastEthernet0/0                            YES   NVRAM     up                    up

FastEthernet0/1            192.168.31.254        YES   NVRAM     up                    up

FastEthernet0/1.10        192.168.10.254       YES   NVRAM     up                    up

FastEthernet0/1.20        192.168.20.254       YES   NVRAM     up                    up

NVI0                             unassigned              NO    unset        up                    up

[Leo Laohoo · Accepted solution]

switchport mode trunk

Is this the only command?  Did you also include "switchport trunk encapsulation dot1q"?

[Talha Abbasi]

Unfortunately, I did NOT issue that command, prior to the command "switchport mode trunk".

and i think that is the cause of this issue.

i think one possible way of solving this would be to ask the local person there to just plug the router into another open port on the switch, then access the switch and issue the command "switchport trunk encapsulation dot1q" on the original port fa0/4, and then reconnect, the router back to that port fa0/4.

[Leo Laohoo]

I'm not sure if this'll work, but change the router's trunk to "ISL" instead of "dot1q".

[Talha Abbasi]

Leolaohoo, i tried changing the encapsulation to ISL, but that didnt work either.  Its probably that other missed command on the switch.

[Talha Abbasi]

Just a quick update.  The issue was resolved after inserting the 'switchport trunk encapsulation dot1q' command on port fa0/4 (connected to router).

I basically their local user at the remote end, to switch the cable from port fa0/4 to any other open port on the switch (in this case it turned out to be fa0/7).  Once that was done, i was able to access the switch, update the switchport setting.  connect the router back to port fa0/4.  and all is well.

thanks everyone that responded.

best regards.

[Leo Laohoo]

May I request if you can mark this thread as "Answered"?