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

Alexandre Petrescu <alexandre.petrescu@gmail.com> Tue, 26 January 2021 15:31 UTC

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Subject: Re: IPv6 certification - IPv6 Router Advertisement Lifetime 0 and Reachable time 10 seconds
To: Nick Hilliard <nick@foobar.org>
Cc: ipv6@ietf.org
References: <CAGeZV=Q=awxFd=vsfBiBC2vt7o3Wkm9ECMSi+UU90ATKmHY32Q@mail.gmail.com> <BAB67E82-9BE8-4E7A-8548-5475E93FD137@employees.org> <CAGeZV=T4B5m7RYrKL4a4peQjZAoJiUqNv7V=0iaz5VdWeSTKng@mail.gmail.com> <08841dc2-9a4e-dacb-174a-a8f4cdfca1c7@gmail.com> <b0b05fa4-532f-98cd-ac41-28cc716a23df@foobar.org> <9ea964a1-4722-c8b4-5c95-e0883b162bf1@gmail.com> <482bac5f-6f8f-5a93-ac2a-e537bd5a2c93@foobar.org> <c95b5952-3299-2700-2643-43c4e71620fe@gmail.com> <9b0e6247-37e3-69d7-b461-588e8f5463f2@foobar.org>
From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Tue, 26 Jan 2021 16:30:47 +0100
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Nick,


Le 25/01/2021 à 20:30, Nick Hilliard a écrit :
> Alex,
> 
> I've read the link you cited, but maybe am missing something here.  Can 
> you be clearer about situations where Router Lifetime = 0 means 
> something other than "do not install this router address in the routing 
> table"?

I agree with you - no I can not be clearer.

When router lifetime == 0 it means that it must not be a default router. 
  It could be used for other things, but certainly it's not a default 
router.

These other things vary.

> The limits you note in rfc 4861 seem to refer to this value not being 
> equal to zero.
> 
> 6275 only mentions AdvDefaultLifetime to say that it should be at least 
> one second.
> 
> The VRRP situation requires that the backup routers use the same RA 
> options, which would presumably not be zero, because then no routers 
> would be active.

YEs.

Alex

> 
> Nick
> 
> Alexandre Petrescu wrote on 25/01/2021 15:39:
>>
>>
>> Le 25/01/2021 à 16:09, Nick Hilliard a écrit :
>>> Alexandre Petrescu wrote on 25/01/2021 14:44:
>>>> YEs, it means to not install rhis router now as a default router, 
>>>> but maybe do it later.
>>>
>>> it means:
>>>
>>>>     A Lifetime of 0 indicates that the router is not a
>>>>     default router and SHOULD NOT appear on the default
>>>>     router list. >
>>> + other stuff like:
>>>
>>>>    Note that system management may disable a router's IP forwarding
>>>>    capability (i.e., changing the system from being a router to being a
>>>>    host), a step that does not necessarily imply that the router's
>>>>    interfaces stop being advertising interfaces.  In such cases,
>>>>    subsequent Router Advertisements MUST set the Router Lifetime field
>>>>    to zero.
>>>
>>> Can you point the bit where RA Lifetime = 0 means "maybe do it later"?
>>
>> In RFC 4861 it is there:> "AdvDefaultLifetime
>>>                      The value to be placed in the Router Lifetime field
>>>                      of Router Advertisements sent from the interface,
>>>                      in seconds.These limits may be overridden
>>>                      by specific documents that describe how IPv6
>>>                      operates over different link layers."
>>
>> In RFC 6275 "Mobile IPv6" it is something about multiple Home Agents
>> (routers), using Router Lifetime fields in Router Advertisements, that
>> might dynamically take a main role there:
>>
>>>       In addition, the sending home agent MAY
>>>       dynamically set the Home Agent Preference value, for example,
>>>       basing it on the number of mobile nodes it is currently serving or
>>>       on its remaining resources for serving additional mobile nodes;
>>>       such dynamic settings are beyond the scope of this document.
>>
>> In RFC 5798 "VRRP" there is something about Master and Backup VRRP 
>> routers there:
>>> 8.2.3.  Router Advertisements
>>>
>>>    When a Backup VRRP router has become Master for a virtual router, it
>>>    is responsible for sending Router Advertisements for the virtual
>>>    router as specified in Section 6.4.3.  The Backup routers must be
>>>    configured to send the same Router Advertisement options as the
>>>    address owner.
>> Alex
>>
>>>
>>> Nick