It could work; there's a whole IETF standard for DHCP failover and it's
implemented beautifully by ISC dhcp. If that's your niche, then ISC is
the way to go.
Simon.
rent instances of dnsmasq on the
network
- use UDP to 'copy' each new lease to the other instance
- on startup, use UDP to request a sync of known leases from the
other instance
- maybe sync local DNS entries as well (though it might be less
desirable for folks
like me who have 850k 'undefined' entries for ads, pron, warez, etc.)
Could this even work? Would it be worth the effort?
N
------------------------------------------------------------------------
*From:* Dnsmasq-discuss
<dnsmasq-discuss-boun...@lists.thekelleys.org.uk> on behalf of Simon
Kelley <si...@thekelleys.org.uk>
*Sent:* Friday, February 4, 2022 4:28 PM
*To:* dnsmasq-discuss@lists.thekelleys.org.uk
<dnsmasq-discuss@lists.thekelleys.org.uk>
*Subject:* Re: [Dnsmasq-discuss] Copying dnsmasq.leases, any issues to
be aware of?
On 04/02/2022 18:16, Chris Green wrote:
I'm looking at ways to provide backup DHCP/DNS with dnsmasq. This is
on a small, fairly 'quiet' home LAN so there aren't dozens of clients
connecting and disconnecting every second. Also if DHCP/DNS is not
available for a few minutes the world won't end! :-)
So, I'm proposing to have dnsmasq installed on two systems, one (say
dns1, 192.168.1.2) is the live DHCP/DNS server, the other (say dns2,
192.168.1.3), both with static IP.
If dns1 dies or needs to be turned off I just copy the dnsmasq
configuration (stored elsewhere as well of course) to dns2 and also
copy the dnsmasq.leases file and [re]start dnsmasq on dns2. Will this
work reasonably OK? I.e. if/when a system on the LAN broadcasts a
DHCP request will it get the same IP again?
It's not a disaster if a system gets a different IP anyway, if
something *really* needs a fixed IP I can add a dhcp-host in the
dnsmasq configuration.
I can even have dnsmasq running on dns2 all the time with it
configured to provide only local DNS and no DHCP, then it's just 'copy
dnsmasq configuration, copy dnsmasq.leases, restart dnsmasq.
(All my systems run syncthing so it's very easy to have pretty much
live copies of files synchronised across systems)
To be honest, even if you didn't bother copying the leases file, most
systems would get the same address. The clients try to renew the lease
on the exiting DHCP server and when they get no response they broadcast
the renewal to try and find a new server. As long as there's no reason
not to, the new server will accept the client's request for the address
it already had.
Cheers,
Simon.
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