Re: [dhcwg] [homenet] What to do when we lose DHCPv4 election?

Steven Barth <> Mon, 17 August 2015 11:46 UTC

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To: Juliusz Chroboczek <>, Michael Richardson <>
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From: Steven Barth <>
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Date: Mon, 17 Aug 2015 13:46:34 +0200
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Subject: Re: [dhcwg] [homenet] What to do when we lose DHCPv4 election?
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Am 17.08.2015 um 12:23 schrieb Juliusz Chroboczek:
>>> When a Homenet router was previously acting as DHCPv4 server for
>>> a link, and subsequently loses an election, should it:
>>> 1. remain silent;
>>> 2. remain silent in response to DHCPDISCOVER, but NAK any DHCPREQUEST; or
>> I think that #2 is probably correct
> Thanks.  What after a renumbering event and the addresses that the client
> requests are no longer onlink?  I'd like a precise reference, if that's
> okay.
At first glance all 3 behaviors seem sensible, while 2 and 3 look more preferable.
However I do not particularly remember all the implications. In any case I'm
thinking of adding "Routers which seize to be elected DHCP
        servers SHOULD - when applicable - invalidate remaining existing
        bindings in order to trigger client reconfiguration."
as a generic recommendation.

>> 1) do Homenet-aware DHCPv4 servers pick the same rfc1918 address spaces to
>>    give out?
> Not necessarily -- if there are multiple prefixes assigned to the link,
> the spec doesn't say which prefix is used by each server.  (Shncpd uses
> them all, which I'm not sure is a good idea.)  Electing a single DHCPv4
> server for each link works around the issue.
There is only one IPv4 "delegated" prefix at a time in an HNCP network.

"In case multiple IPv4
      prefixes are announced, only the one published by the node with
      the highest node identifier is kept among those with a Prefix
      Policy of type 0 - if there is any."

So as long as the Assigned Prefix for a link does not change the DHCPv4
pools stays the same. Individual DHCPv4 servers might use different
algorithms to assign addresses from within the pool.