Re: IPv6 Deployment for the LAN ... anycast

[Perry Lorier <perry () coders net>]

> >  I think for very small/small networks anycast requires a lot of overhead
> > and understanding.  If your big enough to do anycast and/or loadbalancing
> > it's not hard for you to put all three addresses onto one device.
> >
> >     
>
> Anycast isn't really hard - same address, multiple places, routers see what
> appear to be multiple routes to same destination, they choose the least
> expensive.  Only tricky part (for stateless things) is ensuring the route
> announcement is implicitly tied to service availability on that device ...
>
>   

I'm thinking for places like home users and the like which don't really 
run an IGP,  can't correctly identify a router, and when you say 
"anycast" think that you might be talking about a new form of fishing.

> > There are some protocols that anycasting doesn't work well for, they may
> > require multiple instances.
> >     
>
>
> Fair enough; could also standardize something like FD00::<port number>,
> FD00::1:<port number>, and FD00::2:<port number> ... is three addresses
> enough?  (IIRC, the Site-Local based automagic DNS used 2 or three addresses
> ... )
>
>   

3 seems to me to be plenty for most cases.  For some things like NTP you 
might want to have 4 or more.
> OK, so the non-hex converted as above (FD00::x:53; where x=[0,1,2] -
> reserving FD00::/96) covers us to port 9999 based on automatically using
> port numbers (or using automatically registered port numbers, see below).
>
> Maybe FD00::FFFF:xxxx/112 as a block within the above range to be used for
> manual assignment of automatic service (potentially anycast) addresses.
>
>   

Seems sane to me.

> In my humble opinion I'd have them registered, linking them to port numbers
>   
> > means that it's easier on the poor admins brain at 3am while diagnosing
> > faults, but may cause various hassles in the future (see above).
> >
> >     
>
> OK, so register them - but sign up some well-known ones at very comfortable
> addresses, like DNS at 53 :).
> (Or 35 if you prefer hex-conversion ...)
>
> And I am sure some would be concerned about hosts performing any sort of
> automatic service discovery anything, but this atleast has the advantage
> over multicast in that it doesn't require multicast routing or group
> membership / state maintenance, only delivers packets to the nearest (not
> all) instances, etc.
>
>   

Yup, and it makes a sane default, if you want to override with DHCP, or 
some funky RA option, or manual configuration or whatever, then this 
gets out of your way and you don't have to care.
It doesn't involve any code changes on hosts *or* routers to work today.