Re: Misunderstanding IPv6 (Was: IPv6 Books)

[Iljitsch van Beijnum <iljitsch at muada.com>]

On 24-okt-2007, at 17:03, Jeroen Massar wrote:

> > There are other differences. You forgot anycast and you forgot to  
> > mention that only

> Since when is anycast an exclusive IPv6 property? Anycast is a routing
> trick. Nothing more, nothing less.

> People have been using this for ages already.

Note that the anycast that the DNS guys and 6to4 relays use and the  
anycast defined for IPv6 are two very different things. The former is  
indeed a routing trick (hack, really), while the latter is something  
that's done on the link layer. From a book I happen to know well:

"Multicast and anycast addresses may be used as destination addresses  
in packets, but only unicast addresses may be used as source  
addresses. Also, only routers may be configured with an IPv6 anycast  
address.
This means that strictly, anycasting services such as the DNS isn’t  
compatible with RFC 3513. After all, for anycast DNS to work, the  
anycast address must be present on more than one DNS server (which  
presumably are hosts and not routers), and the responses to DNS  
queries are sent back with the destination address of the query (the  
anycast address) as the source address. The host that sent the query  
wouldn’t recognize the response if it came from a different address.  
However, anycasting services is rarely done using the actual IPv6  
anycast link-level mechanism, where several systems configured with  
the same anycast address are connected to the same subnet."

However, I don't believe the IPv6 link anycast service is all that  
widely implemented in routers.
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