Re: [PATCH] anycast support for IPv6, linux-2.5.31

From: Pekka Savola (pekkas@netcore.fi)
Date: Fri Aug 30 2002 - 01:37:38 EST


On Wed, 28 Aug 2002, David Stevens wrote:
> 1) The API
> Although the RFC's liken anycasting to ordinary unicasting, I think
> it's more appropriate to tie it closely to particular applications, so I've
> chosen an API similar to multicasting. So, rather than having a permanent
> anycast address associated with the machine, particular applications
> that use anycasting can join or leave "anycast groups," and the machine will
> recognize the anycast addresses as its own when one or more applications have
> joined the group.
> So, for example, someone using anycasting for DNS high availability
> can add a join to the anycast group in the server and as long as the DNS server
> is running, the machine will answer to that anycast address. But the machine
> will not respond to anycasts when the service that's using it isn't available,
> so a broken server application that has exited won't deny that service if
> there are other working members of the anycast group on other hosts.
> I don't know if that's controversial or not-- the RFC's are written
> more from the external context, but seem to imply a model along the lines of
> using "ifconfig" to add anycast addresses. I think that model doesn't fit the
> best uses of anycasting, but I'd like to hear your thoughts on it.
> The application interface for joining and leaving anycast groups is 2
> new setsockopt() calls: IPV6_JOIN_ANYCAST and IPV6_LEAVE_ANYCAST. The arguments
> are the same as the corresponding multicast operations. The kernel keeps a
> reference count of members; when that goes to zero, the anycast address is not
> recognized as a local address. While nonzero, the host listens on the solicited
> node for that address, sends advertisements in response to solicitations (with
> override=0) and delivers packets sent to the anycast address to upper layers.
> There's also an in-kernel interface described below, which is used by
> IPv6 mobility, for example.

Before going too much down this path, I think one should write an Internet
Draft about the proposed API (should be quite short & simple) and see what
kind of response it has in the relevant working groups.

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords

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