It's Ars Tech's turn to bang the IPv4 exhaustion drum

Wed Aug 20 08:47:39 UTC 2008

On 19 aug 2008, at 22:29, Kevin Loch wrote:

> I thought there was an issue with duplicate address detection with / 
> 127
> (RFC3627)?

Don't know about that, but the all-zeroes address is supposed to be  
the all-routers anycast address. Cisco doesn't implement this, so /127  
works on those, but there are some other vendors that do, so /127  
won't work on those boxes. (And wouldn't it be funny if Cisco decided  
to start implementing the all-routers anycast address...)

> /126 should work and lots of folks use /112 which is a more
> human-friendly bit boundary.  /112 is also good for multiple access
> vlans and just about anything that isn't using autoconfig.

I like using EUI-64 addressing, i.e.:

!
interface vlan666
  ipv6 address 2002:dead:beaf:666::/64 eui-64
!

This has the advantage that you don't have to explicitly assign an  
address to each router, it all works out automatically and you can  
copy/paste configs from one box to the other.

I also like to put the VLAN ID in bits 48 - 63. This makes the IPv6  
addressing plan REALLY simple...