> From: John C Klensin <john-ietf(_at_)jck(_dot_)com>
> Of course, multiple A records works, is out there, and have worked for
> years. But they worked better before we introduced routers (i.e., when
> the hosts with multiple A records really had interfaces on different
> networks). Today, it effectively implies having multiple addresses on
> an interface and multiple "local" address prefixes running around on
> the same physical LAN segment.
> ...
> Perhaps more important, as Noel points out, it doesn't scale very well,
> at least in terms of the routing fabric.
Sorry? What I said doesn't work for the routing, in terms of scaling to many
small sites, is for a multi-homed site to have a single address prefix, which
is then globally advertised. (That's the most common tack for multi-homing
support in IPv4 to date, which is what you were talking about.)
Having multiple addresses for a host (which has only a single physical
interface, but which is in a site which is multi-homed) is in fact the only
approach whose effects on the routing does scale (within anything like the
current routing architecture, i.e. packets which include only source and
destination addresses, as opposed to a source route).
> as I tried to point out, address preservation policies have had
> trickle-down effects that make it impractical for small enterprises.
It is an interesting point (as Daniel Senie also just pointed out) that
multiple addresses -> faster consumption of the address space.
However, since to avoid a size explosion in the routing tables, those
multiple addresses do have to be connectivity-dependent (political
translation - "provider-dependent"), I don't see how address preservation
policies have made this approach "impractical for small enterprises". My
understanding of current allocation policies is that ISP's can get enough
addresses to cover their customers. If company X is a customer of both ISP P
and ISP Q, I would assume that both P and Q don't have a problem getting
enough space to cover their customers - including X.
(Or were you speaking of the "one address block, globally advertized"?)
Noel