DHCPD is not re-using addresses

Bob Proulx bob at proulx.com
Mon Mar 14 07:02:47 UTC 2016

CLOSE Dave wrote:
> When I run PXE on a new machine, I see the Anaconda (the Fedora
> installer) makes at least three requests for a dynamic address. So far
> as I can tell, all of the requests are identical.
> Even though all the requests originate from the same MAC address, the
> DHCP server gives each request a unique response. As the address leases
> take time to expire, I quickly run out of available addresses. Much more
> quickly than I should.

As Steinar Haug mentioned it is likely that the different clients are
submitting different client ids.  In which case DHCP requires
responding with a different address.

Have you considered using shorter lease times for your volatile
clients?  That way they will expire in a shorter time period and be
available to be reused.  There are likely much better ways to
accomplish this but this is what I do.  It prevents running out of
addresses from the pool when consuming them quickly.  Here I have a
small pool sufficient for me but you might need to decrease times and
a larger pool.  But hopefully it gives you the idea.

class "volatile"  {
  match if substring(option vendor-class-identifier, 0, 3) = "d-i" or
           substring(option vendor-class-identifier, 0, 9) = "PXEClient" or
           substring(option vendor-class-identifier, 0, 9) = "Etherboot" or
           substring(option vendor-class-identifier, 0, 8) = "anaconda" or
           substring(option vendor-class-identifier, 0, 8) = "volatile";

subnet netmask {
  option subnet-mask;
  option routers;
  pool {
    failover peer "dhcp-failover-peers";
    deny members of "volatile";
    default-lease-time 43200;
    max-lease-time 86400;
  pool {
    failover peer "dhcp-failover-peers";
    allow members of "volatile";
    default-lease-time 1800;
    max-lease-time 1800;

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