IPv6 Subnet tool

[Joe Abley]

On 13 Jan 2009, at 19:22, MSC wrote:

> I am fairly new to IPv6 and recently start reading about it. We are  
> planning to get an IPv6 block and i need to get some understanding  
> and hands one with the v6 subnetting. I appreciate if someone could  
> shrare the knowledge about some free ipv6 subnet tool which could  
> help subnet a /40 or /48 etc.

Others here might well have different advice, but with fixed-sized  
subnets you don't really need a tool to do anything; you just need an  
easy-to-remember way of generating a unique number per subnet.

So, if you're assigned 2607:f2c0:ffff::/48 by your ISP, and all your  
subnets are /64s, then you just have to number them using the middle  
16 bits. So, subnet xxxx would be numbered 2607:f2c0:ffff:xxxx::/64.

In networks with a switched ethernet core, one approach is to use the  
VLAN tag, either converted to hex or just entered as-is (so, binary- 
coded decimal). So if you want to figure out how to number devices on  
vlan 297, just use 2607:f2c0:ffff:297::/64. You could use special  
"vlan" numbers (e.g. 0, f000, whatever) to identify blocks of  
addresses to number other stuff that doesn't have a VLAN tag, like  
point-to-point links, loopbacks, etc.

If you have a bunch of sites, and more address space than a /48, then  
maybe use one /48 per site.

There are surely many possible variations. But it seems to work well  
to use fixed-sized subnets and encode an identifier into the prefix.


Joe