[Dnsmasq-discuss] Make RA_INTERVAL configureable? Deprecate old prefixes?

[Simon Kelley]

On 24/07/13 19:16, Uwe Schindler wrote:
> Hi,
>
>> RA's are not the same as DHCP, there's no such thing as a "lease
>> time". What there is, is preferred and valid lifetimes. What should
>> happen is that when old address is about to go away, the address
>> for that prefix on the network adaptor should have its preferred
>> lifetime set to zero, and dnsmasq will then notice that and send
>> RA's with the preferred lifetime also set to zero.
>
> I meant the life time, it was just a typo somehow :-) The idea here
> was to send preferred_lifetime=0 in RAs for prefixes that disappeared
> from the interface to "inform" the clients that they are no longer
> useable (my provider does not route old prefixes after a reconnect
> with PPP). Currently you have to set the lifetime very low (which
> produces more traffic on the wire) or manually delete or switch
> on/off the network adaptors once the router reconnects or the prefix
> changes for some reason.
>
> My proposal is to keep a list of "previous prefixes" from the
> constructor:ethX code and also send those prefixes, but with
> lifetime=0 to inform all client to no longer use that address. Those
> 0-lifetime RAs should be sent at least for the length of the original
> lifetime. Radvd has code to handle this (although it’s a bit buggy).
>


My understanding of this is that it's something that should happen in 
the DHCP client and/or ISP DHCP server.

Ie, when the prefix has to change, the ISP's DHCP server renews the 
existing prefix delegation, but with the preferred lifetime==0. It also 
offers a new prefix delegation. The old and new prefixes get installed 
in the network adaptor with the preferred lifetime values. Dnsmasq 
starts to advertise the new prefix and continues to advertise the old 
prefix, but with the pref-lifetime at zero taken from the value in the 
adaptor.


Again, this is new territory, I'm not saying has to be done like that, 
but that's the process I was thinking of when I wrote the existing code.


Cheers,

Simon.