Posts Tagged ‘cisco’

Telenet modem and Cisco switch [en]

mardi, avril 25th, 2017

This is one thing among many others i have to say against Telenet: once the modem reboots (and it can be quite often, always requested by Telenet), the port of the switch just shuts down and block all access to the modem. Very embarrassing…

Let’s see what’s going on in the switch via the serial console:

Switch>enable
Switch#show interface status err-disabled

Port Name Status Reason Err-disabled Vlans
Fa0/23 err-disabled loopback
Switch#

Something you need to know about the Cisco is that the switch send keepalive packets down all active ports. When the modem reboots, it’s echoing the keepalive packet back to the switch. The switch freaks out and disable the port, cutting you off the internet.

The solution is pretty easy: all you need to do to is to turn off keepalives for that interface:

Switch#config t
Switch(config)#Interface fa0/23
Switch(config-if)#no keepalive
Switch(config-if)#end 
Switch# copy running-config startup-config
Switch#

Now that we disabled the keepalive,it’s time to re-enable the port. You have to manually shut it down and re-enable it to clear the err-disable state:

Switch#config t
Switch(config)#Interface fa0/23
Switch(config-if)#shutdown
Switch(config-if)#no shutdown
Switch(config-if)#end 
Switch#

Enjoy your recovered internet. 🙂