Holger, >> >>>>> Imagine a setup with *two* routers. One of them has broken Internet, >>>>> the other is working. How can the hosts decide if both keep announcing >>>>> themselves as "I can reach anything"? >>>> >>>> in the general case the host still has to take the 'I can reach anything' >>>> announcement with a pinch of salt. >>>> and it should be able to try both (or more) connections and react >>>> accordingly when one fails. >>> ...which is the default host behaviour if the OS supports RFC4861. >>> Sadly some "user friendly" network mangers breaks this and setting a >>> static route with a better metric to just one(!) router. >> >> not really. that only covers the first hop. any failure anywhere else along >> the path would not be dealt with by 4861. > Yes, of course, you're right. > > But coming back to Brians problem. > The behavior of his router is confirm to RFC7084: > > "G-4: By default, an IPv6 CE router that has no default router(s) on > its WAN interface MUST NOT advertise itself as an IPv6 default > router on its LAN interfaces. That is, the "Router Lifetime" > field is set to zero in all Router Advertisement messages it > originates [RFC4861]." > > But this would break local connectivity if the router does not also > fulfill L-3 > > "L-3: An IPv6 CE router MUST advertise itself as a router for the > delegated prefix(es) (and ULA prefix if configured to provide > ULA addressing) using the "Route Information Option" specified > in Section 2.3 of [RFC4191]. This advertisement is > independent of having or not having IPv6 connectivity on the > WAN interface." > > So far so good. But if the host doesn't honour the RIO then again local > connectivity is broken. > > So take a look at the reasons for this. The second paragraph of 3.2.1 says: > > "At the time of this writing, several host implementations do not > handle the case where they have an IPv6 address configured and no > IPv6 connectivity, either because the address itself has a limited > topological reachability (e.g., ULA) or because the IPv6 CE router is > not connected to the IPv6 network on its WAN interface. To support > host implementations that do not handle multihoming in a multi-prefix > environment [MULTIHOMING-WITHOUT-NAT], the IPv6 CE router should not, > as detailed in the requirements below, advertise itself as a default > router on the LAN interface(s) when it does not have IPv6 > connectivity on the WAN interface or when it is not provisioned with > IPv6 addresses. For local IPv6 communication, the mechanisms > specified in [RFC4191] are used." > > At the end, the whole behavior is because some host have problems in > handling situations where they have an IPv6 address configured and now > internet connectivity. But the solution to this requires that the host > is able to understand and work with RIO options, which seams to be "at > the time" not generally the case. > > Do we replace one evil by another?
Yes, we did. This work was done at the time of "host IPv6 brokenness". Perhaps time to revisit those decisions? Best regards, Ole
