Dhcpd failover with fixed IP only : thoughts ?

Glenn Satchell glenn.satchell at uniq.com.au
Mon Sep 9 11:38:40 UTC 2013

On Mon, September 9, 2013 9:07 pm, tom wrote:
> Hi Glen,
>> Fixed IP and dhcpd, I assume you mean you use host statements with
>> fixed-address only? [..]
> Yes. Although not exactly because I use a pool containing only one IP
> because dhcpd 4.1.1P1 does not support host statement based on option82.
> Reference: http://www.miquels.cistron.nl/isc-dhcpd/
>> Fixed-address is a special case within the server in that it doesn't get
>> handled like a dynamic lease, so each server can hand out the same
>> address
>> and it will all "just work".
> Great! Can you provide more information about "doesn't get handled like
> a dynamic lease" ? I am asking mainly because I do use host host {} but
> a 'fake' pool.

Can't put my hand on a reference right now, but I'd suggest a close
reading of dhcpd.conf. Essentially because a fixed-address statement means
it always hands out only one Ip address for a host, rather than searching
a pool, there are some short cuts in the internal code paths. For instance
no lease is ever written to the dhcpd.leases file.

Now if you use pools with 1 address, there will still be a full lease
written, however I think it will still work for you because there is only
one IP address to be assigned to each client. So if the client queries
several servers they will (should?) always give the same answer. So I
still suggest that you could run multiple serve3rsd with identical configs
and no need for dhcpd failover config. In fact dhcpd failover will not
work because it needs at least two IPs in each pool so it can split them
between the two servers.

> Thanks Glenn

My pleasure to try and help.


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