Choice of address for IPv6 default gateway

Owen DeLong owen at delong.com
Wed Jan 25 17:39:52 CST 2012


On Jan 25, 2012, at 8:40 AM, Ray Soucy wrote:

> On Wed, Jan 25, 2012 at 10:06 AM, Leo Bicknell <bicknell at ufp.org> wrote:
> 
>> I don't think the industry has really found a best practice to
>> document yet.  There are people trying different ideas.  We find
>> the following convention allows us to keep things organized:
>> 
>> <prefix>::1                  - Default gateway
>> <prefix>::<last octect IPv4> - Statically assigned servers.
>> <prefix>:<eui-64>            - Auto-configured host
> 
> This is essentially what we do (except we use the hex value of the
> last octet, so .34 would be ::22, probably just the purist in me).
> 

Having done both hex-conversion and BCD (in fact I mention both possibilities in the IPv6 courses that I teach), I have to say that the purist loses to the pragmatist in my mind and BCD makes much more sense. You can, actually, safely BCD up to the last three IPv4 octets in an IPv6 address without violating the 12-bits of zeroes rule to avoid EUI-64 collisions, so, for example, 10.1.2.3 could become <prefix>::1:2:3, or, 10.209.198.144 could be <prefix>::209:198:144.

> If you have an environment where hosts will be statically configured,
> then you probably want to use a global default, if only to avoid
> confusion from users or poorly written software that expects the
> default to be in the same prefix as the address.
> 

Well, any software should be able to handle a link-local default, but, otherwise, yes.

> If people understand their prefix is 2001:DB8::/64, and the gateway is
> 2001:DB8::1 it raises a lot less questions than "your prefix is
> 2001:DB8::/64 but your default router is FE80...".
> 

People will have to get used to the fe80 thing pretty quickly anyway, since that's what you get with RAs regardless.

Owen




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