Category: Cisco

Cisco err-disable recovery

Did it also happen to you, that a port of a remote switch went to err-disable and you had to drive to that location to reset it?

Or you have users in meeting rooms, who plug in the same network cable in two different switch ports? Nothing happened, spanning-tree portfast bpduguard enable was set.  But the ports went down, and nobody realised it?

You can avoid this problem with the setting

errdisable recovery cause all
errdisable recovery interval 180

With this setting, the switch brings up the port after 180 seconds. If the problem still exists, the port goes into err-disable again. If it is fixed, the port comes up again.

IPv6 Tunnel with Cisco

Cisco does support PPPoE with IPv6, so if your provider does support IPv6, you can do a native connection. If not, you can establish a Tunnel to SIXXS or another IPv6 provider.

ipv6 unicast-routing
interface tunnel0
  description IPv6 uplink to SixXS
  no ip address
  ipv6 enable
  ipv6 nd suppress-ra (<12.4)
  ipv6 nd ra suppress (>=12.4)
  ipv6 address [Your IPv6 Endpoint]/[Prefix Length]
  ipv6 mtu 1280 (or other MTU value)
  tunnel source [Your IPv4 Endpoint]
  tunnel destination [PoP IPv4 Endpoint]
  tunnel mode ipv6ip
!
ipv6 route 2000::/3 [PoP IPv6 Endpoint]

IPv6 Address renumbering

IPv6 uses provider aggregated IP addresses. In the documentation you can read, how easy it is to do address renumbering.

You can specify a general prefix on a device. If you need to change the address, you have to change the global prefix only, and all addresses got the new prefix on this device.

On cisco devices it is:

ipv6 general-prefix PROD 2001:DB8:1234::/48
!
interface Vlan1
 description Management Network
 ipv6 address PROD ::1:0:0:0:2E1/64
 ipv6 enable
!
interface Vlan2
 description Management Network
 ipv6 address PROD ::2:0:0:0:FF/64
 ipv6 enable
!

Now you change the address of the generel-prefix PROD and all your IP addresses on this device are changed.