Subject: Re: [v6ops] Operational Headache: Upstream liveness

From: "Rajiv Asati (rajiva)" <[email-masked]>
Date: Fri, 29 Mar 2019 12:04:17 +0000

Mikael,

Thanks for the clarity. Looking at RFC7084 3.2.1 and 4.1 sections, the scenario of a previously advertised/reachable default router on WAN link becoming unreachable, is not explicitly mentioned.

https://tools.ietf.org/html/rfc7084#section-3.2.1

   host implementations that do not handle multihoming in a multi-prefix
   environment [MULTIHOMING-WITHOUT-NAT<https://tools.ietf.org/html/rfc7084#ref-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.

https://tools.ietf.org/html/rfc7084#section-4.1

   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<https://tools.ietf.org/html/rfc4861>].

   G-5:  By default, if the IPv6 CE router is an advertising router and
         loses its IPv6 default router(s) and/or detects loss of
         connectivity on the WAN interface, it MUST explicitly
         invalidate itself as an IPv6 default router on each of its
         advertising interfaces by immediately transmitting one or more
         Router Advertisement messages with the "Router Lifetime" field
         set to zero [RFC4861<https://tools.ietf.org/html/rfc4861>].

--
Cheers,
Rajiv

From: Mikael Abrahamsson <[email-masked]>
Organization: People's Front Against WWW
Date: Friday, March 29, 2019 at 5:56 AM
To: Fred Baker <[email-masked]>
Cc: Rajiv Asati <[email-masked]>, "[email-masked]" <[email-masked]>
Subject: Re: [v6ops] Operational Headache: Upstream liveness

On Fri, 29 Mar 2019, Fred Baker wrote:

Well, that seems like a reasonable hope. I think that Mikael is saying
that in IPOE environments they might not be compliant, or compliant
implementations still have a problem. I think the key point here is to
uncover what the issue might be in the context he is discussing, as
opposed to simply dismissing it.

RFC7084 doesn't say (afaik) to stop announcing yourself as a default
router on LAN when your default GW LL next-hop becomes unreachable, and
then start doing RS, throw away your DHCPv6 prefix etc, and start to go
back into whatever you do in an WAN interface down/up situation.

This is what is unspecified. We know pretty well what to do in an WAN
interface down/up event, but not "softer" errors such as when the RA
sending LL next-hop goes into ND unreachable state.

--
Mikael Abrahamsson    email: [email-masked]<mailto:[email-masked]>