On Oct 23, 2010, at 7:26 AM, Mark Smith wrote:
On Fri, 22 Oct 2010 15:42:41 -0700 Owen DeLong <owen@delong.com> wrote:
Actually, it's not pointless at all. The RA system assumes that all routers capable of announcing RAs are default routers and that virtually all routers are created equal (yes, you have high/medium/low, but, really, since you have to use high for everything in any reasonable deployment...)
No it doesn't. You can set the router lifetime to zero, which indicates to the end-node that the RA isn't announcing a default router. In this case, it may be announcing M/O bit, prefix or other parameters.
DHCPv6 can selectively give different information to different hosts on the same wire segment.
RA cannot.
That was not the assertion you made.
You said that
"The RA system assumes that all routers
capable of announcing RAs are default routers"
and I said, no, that is not the case if you set the RA lifetime to zero. To cite explicitly, RFC4861 says,
Right... I oversimplified the point I was attempting to make and you called me on it... Move on.
Router Lifetime 16-bit unsigned integer. The lifetime associated with the default router in units of seconds. The field can contain values up to 65535 and receivers should handle any value, while the sending rules in Section 6 limit the lifetime to 9000 seconds. A Lifetime of 0 indicates that the router is not a default router and SHOULD NOT appear on the default
Narten, et al. Standards Track [Page 20] ^L RFC 4861 Neighbor Discovery in IPv6 September 2007
router list. The Router Lifetime applies only to the router's usefulness as a default router; it does not apply to information contained in other message fields or options. Options that need time limits for their information include their own lifetime fields.
I was not making any statements about whether DHCPv6 could be selective about providing certain options to selected end-nodes.
You might think I'm being overlay pedantic, however changing the question to then disagree with answer that doesn't agree with yours is being disingenuous.
There are real environments where it's desirable to have a way to tell different clients on a network to use different default gateways or default gateway sets.
I wouldn't necessarily disagree, although in my experience they're really quite rare, to the point where segmenting them into a separate subnet, via e.g. a different VLAN, becomes a somewhat better and easier option.
While I would agree with you operationally, sometimes they involve software that discovers other devices by broadcast and does not permit other mechanisms. I've seen environments where they're able to deal with this in IPv4 because of this flexibility in DHCPv4 and would be limited to static addressing in IPv6 because it lacks this ability. Owen