[Dnsmasq-discuss] dnsmasq on an IPv4 /32 interface

Geert Stappers stappers at stappers.nl
Mon Sep 21 22:08:49 BST 2020


On Tue, Sep 22, 2020 at 05:32:56AM +1000, Paul Gear wrote:
> Hi all,
> 
> I've been trying to solve the same problem described in this blog post:
> https://blog.fhrnet.eu/2020/03/07/dhcp-server-on-a-32-subnet/

Interesting read, however I not sure how interesting the "problem" was.


> In a nutshell, the situation is a VM host which performs routing and
> firewalling for all its guests, providing an isolated IPv4 /32 (and in
> my case an IPv6 /64 or /128 as well) to each VM guest, and using
> interface routes on the host to direct traffic to each guest, without
> wasting IPv4 addresses on /31 or /30 point-to-point links.
> 
> The post claims that the configuration noted (a single /32 allocated to
> the host which is configured on every client-facing interface) is only
> possible at present with ISC DHCP.  I've tested a number of different
> configurations of dnsmasq, and this seems to be correct.  I'm hoping
> someone experienced in the dnsmasq code base can confirm or deny this.
> 
> Assuming this is currently a limitation, I'd like to work on adding
> support to dnsmasq for this scenario.  I'm not experienced with the code
> base (although I've read some of the relevant portions and believe it
> should be possible), so I'm hoping also for some guidance on whether
> this functionality would be accepted into the code base, and if so, how
> it might appear in the configuration.
> 
> My initial thought was that there wouldn't need to be any explicit
> configuration; rather, if a DHCP request is received on an interface
> with a /32 mask (or perhaps on an interface with a non-unique address on
> the host), the usual restrictions around interface matching would be
> relaxed, and an address would be given out either from the
> statically-defined hosts, or from a pool which doesn't match any
> interface on the host.  When giving out IPv6 addresses, my thought was
> that things would mostly work the same if a DHCPv6 request was received
> on an interface with only link-local addressing configured.
> 
> Thanks in advance - I hope all this makes sense and look forward to
> discussing it further with you.

I think that discussion will go quickly silent
when only one person can reproduce the challenge.


 
> Regards,
> Paul

Groeten
Geert Stappers
-- 
Silence is hard to parse



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