At 10:27 AM 11/21/2003, Thomas Narten wrote:
Bob Hinden <[EMAIL PROTECTED]> writes:
> John,
> > For those IPv6 nodes that implement DHCP, those nodes MUST use DHCP > > upon the receipt of a Router Advertisement with the 'M' flag set (see > > section 5.5.3 of RFC2462). In addition, in the absence of a router, > > IPv6 Nodes that implement DHCP MUST attempt to use DHCP. > >to: > > Nodes that implement DHCP MUST use DHCP upon the receipt of a > > Router Advertisement with the 'M' flag set (see section 5.5.3 of > > RFC2462). In addition, in the absence of a router, > > IPv6 Nodes that implement DHCP MUST attempt to use DHCP. In this > > context, 'use DHCP' means trying to obtain both address(es) and > > other configuration information through DHCP.
For my tastes, there is too much protocol specification above (use of MUST language). Better to just cite the existing standards.
Yes, I agree.
> Please remind me why the "in the absence of a router" text is there. I am
> having a hard time thinking about a scenario where there would be a DHCP
> server, but no router. The presences of a DHCP relay agent would also need
> a router to be useful.
Perhaps because folk have forgotten about existing text in 2461 & 2462? :-)
I figured there must be some reason why this text was there. That's why I asked :-)
From section RFC 2461 6.3.7:
> If a host sends MAX_RTR_SOLICITATIONS solicitations, and receives no > Router Advertisements after having waited MAX_RTR_SOLICITATION_DELAY > seconds after sending the last solicitation, the host concludes that > there are no routers on the link for the purpose of [ADDRCONF]. > However, the host continues to receive and process Router > Advertisements messages in the event that routers appear on the link.
RFC 2462, Section 5.5.2 says:
> 5.5.2. Absence of Router Advertisements > > If a link has no routers, a host MUST attempt to use stateful > autoconfiguration to obtain addresses and other configuration > information. An implementation MAY provide a way to disable the > invocation of stateful autoconfiguration in this case, but the > default SHOULD be enabled. From the perspective of > autoconfiguration, a link has no routers if no Router Advertisements > are received after having sent a small number of Router Solicitations > as described in [DISCOVERY].
We can debate whether the current text makes sense, but it reflects the thinking at the time...
Agreed. Since I don't think DHCPv6 wasn't very far along at the time this was written, I wonder if we were thinking about other kinds of stateful autoconfiguration that might be useful when there was no router. Must be in the mail archives.
However, this doesn't seem like a useful behavior now. I think it would be best to not restate it in node requirements.
Also, I think we should revisit this text in the RFC2462bis effort. Changing the MUST to MAY in the 5.5.2 paragraph looks like the right change to me, but that's a different email thread.
Bob
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