Monday, March 18, 2013

IPv6 MTU discovery

Thanks to it looks like it's easy to discover the IPv6 MTU (Maximum Transmission Unit):

$ ping6 -c1 -M do -s 10000  | grep mtu | awk '{ print $NF }' 


So the IPv6 MTU to is 1500.

From another system, the MTU is 1480:

$ ping6 -c1 -M do -s 10000  | grep mtu | awk '{ print $NF }'


Easy, isn't it?

For old-skool IPv4, the output of ping is a bit different, so the awk parsing is a bit different:

$ ping -c1 -M do -s 10000 | grep mtu | awk '{ print $NF }' | sed -e s/\)//



Sunday, March 10, 2013

Dutch ISP Telfort introduces IPv6

After conducting an IPv6 pre-pilot (see, Dutch ISP pilot Telfort has silently introduced IPv6 for all its DSL (VDSL and ADSL) customers. I don't know about its FttH customers. And mobile customers probably have to wait.

Telfort's IPv6 is opt-in; you have to enable it in your Zyxel modem. This is how:

  • Log in on your Zyxel modem at 
  • Go to Network Setting -> Broadband. At the top of that page, check which connection is used: VDSL or ADSL. Then find that entry in the table below, and click on the corresponding "Modify" icon on the far right
  • In the windows that pops up, at "IPv6/IPv4 DualStack" click enable. More below, enable "6to4 Tunneling" and check "6RD Enable". Then click the Apply button
  • Final check: the column IPv6 should now be on "enable" at your VDSL or ADSL line.

That's it. You should now have IPv6. Check via or If not, reboot your  modem and computer once.

Technology used is 6RD. Address prefix is 2A00:CD8::/32

Telfort's mother company KPN yet has to introduce IPv6.