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

Nick Hilliard <nick@foobar.org> Mon, 25 January 2021 19:30 UTC

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Subject: Re: IPv6 certification - IPv6 Router Advertisement Lifetime 0 and Reachable time 10 seconds
To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Cc: ipv6@ietf.org
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From: Nick Hilliard <nick@foobar.org>
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Date: Mon, 25 Jan 2021 19:30:22 +0000
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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"?

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.

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