stepping away from ULAs, I should think the point is to propagate
routing configuration information throughout a small zero-config
network. The several routers on a given LAN want to be in the same
subnet; if there are several subnets on the same LAN, with the
possible exception of DMZ routers to specific ISPs, they want to each
be in all of them. ULA management is special case of this.
Going back to the figure I referenced (figure 3 of http://tools.ietf.org/html/draft-baker-ipv6-prefix-subdelegation)
, you have a single LAN with five routers on it, plus LANs beyond
three of those. Two of the routers connect to ISPs and presumably get
prefixes delegated to them by those ISPs. In addition, to cover the
case in which one has no connectivity to either ISP (and therefore no
prefix lease from them), one needs a ULA. So in this network, thee is
a need for three prefixes, two of which are global, plus link-local
addressing. On each LAN, apart from local policy that might have one
of the offices using one ISP and the other using the other ISP or some
such thing, you want an IP subnet from each of those prefixes, and you
want all of the routers on the LAN in each subnet, with the possible
exception of the two ISP-facing routers being in each other's
delegated prefixes.
This can be accomplished by manual configuration, by a DHCP option
that to my knowledge is not currently defined, or by listening to each
other's RAs as I suggested. How would you suggest achieving it?
As to what to do when one loses connectivity to the critical router,
and again considering such a network, there are some interesting
issues. I tend to think the best bet is to use some form of lease
concept rather than making the prefix suddenly go away throughout, but
can be argued into other positions.
On Jan 13, 2010, at 2:27 AM, Wojciech Dec (wdec) wrote:
Perhaps a basic question or two: What is the purpose of the ULA being
advertised on the shared segment, and is the intent for the "2nd
router"
to auto-config itself an address in the ULA space and begin
advertising
that ULA too?
http://www.ipinc.net/IPv4.GIF
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