Re: IPv6 certification - IPv6 Router Advertisement Lifetime 0 and Reachable time 10 seconds

Isaac <> Sun, 24 January 2021 19:10 UTC

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From: Isaac <>
Date: Mon, 25 Jan 2021 00:40:33 +0530
Message-ID: <>
Subject: Re: IPv6 certification - IPv6 Router Advertisement Lifetime 0 and Reachable time 10 seconds
To: Ole Troan <>
Cc: Nick Hilliard <>,
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Thanks Ole. Do hosts rely on RA packets for updating neighbor cache
post determining that the router is no longer the default gateway? They can
use NS/NA packets also right?

BTW, what do you think is the configuration/scenario on a router which
sends a RA packet with lifetime 0 and reachable time 10 seconds? Are you
aware of any particular vendor's configuration which generates such packets?


On Sun, Jan 24, 2021 at 10:20 PM Ole Troan <> wrote:

> Isaac,
> The two variables are independent.
> The example you cited is perfectly fine.
> the RA lifetime says: “don’t use me as a default router” and the reachable
> time configures hosts on the link to consider a neighbor entry in the ND
> cache reachable for 10s (for NUD).
> Best regards,
> Ole, 6man co-chair
> On 24 Jan 2021, at 17:07, Isaac <> wrote:
> Thanks Nick for the timely response!!!
> I understand your comment regarding the prerogative of IPv6 forum in this
> regard. Meanwhile, we need a technical answer/analysis of the combination
> of RA lifetime 0 and Reachable time 10s whether that makes sense or whether
> it was clearly envisioned in the original IPv6 design. We know that RFC
> puts forth a set of 'may', 'might' conditions which are deemed optional in
> certian corner cases (possibly). We are already having discussions with the
> certification body but we need to go with a clear cut technical response of
> whether RA lifetime 0 and reachable time 10 seconds makes sense or not.
> Same way, section 6.2.3 in RFC4861 puts forth a 'might' condition. RA with
> a lifetime 0 and with advertised prefixes might mean that there may be a
> second router in the LAN segment which advertises a positive lifetime. And
> this itself is a corner scenario we believe and common scenario would be a
> single router in a LAN segment who always advertises with a positive
> lifetime until he decides to cease to be default gatewway for clients
> (probably he is ging down as well). But the combination of RA lifetime 0
> and reachable time 10 seconds doesn't make sense to us and we are clueless
> as to how that can be supported. We do not want to deisgn some throw away
> logic just for certfication purpose and we do think thats neither the
> purpose of certification bodies nor the end customers. We need a solid
> technical answer from the IETF IPv6 official body in this regard. Please
> review and respond.
> Thanks,
> Isaac.
> On Sun, Jan 24, 2021 at 5:38 PM Nick Hilliard <> wrote:
>> Isaac wrote on 24/01/2021 11:02:
>> > At the moment, we are unable to find a scenario (real world usecase) to
>> > support RA lifetime of 0 and RA reachable time of 10 seconds. Please
>> > review and respond.
>> Isaac,
>> you're referring to an IPv6 Forum document, so they might be more
>> qualified to give an answer to your question.
>> As a potential pointer, rfc4861 documents the following case in section
>> 6.2.3:
>> >    A router might want to send Router Advertisements without advertising
>> >    itself as a default router.  For instance, a router might advertise
>> >    prefixes for stateless address autoconfiguration while not wishing to
>> >    forward packets.  Such a router sets the Router Lifetime field in
>> >    outgoing advertisements to zero.
>> Nick
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