IPv6 Address Planning

[Iljitsch van Beijnum]

On 13-aug-2005, at 13:34, Dan Reeder wrote:

> the /126 is between the the customer and the isp. Two usable  
> addresses for the point to point.

Actually it's three usable addresses.  :-)

You can't use the all-zeros address because it's supposed to be the  
subnet all-routers anycast address, but the all-ones address is fair  
game.

> The customer gets a /48 assigned to them to do whatever they want.
> You ask why /126? I ask you: why not?

Since you ask...

- it's inconvenient because you need to do (some) binary math to  
determine which addresses go together. With a /124 you can use the  
last digit for this, so that's easier

- doesn't accommodate for the 128 reserved anycast addresses, but a / 
120 does

- you need to keep track of which router has which address. with  
eui-64 addressing and a /64 you don't (whether this is useful depends  
on whether you need to refer to the other side's address elsewhere.  
for customers you generally do to route their /48 or what have you to  
them, for internal stuff you don't, routing protocols take care of it)