[Dnsmasq-discuss] 3 secs dhcp delay

[Geert Stappers]

On Fri, Jan 18, 2019 at 10:36:19AM +0100, Harald Dunkel wrote:
> On 1/17/19 11:58 PM, Simon Kelley wrote:>
} } http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2019q1/012822.html
} } }  ... VPN ...
> > The delay is while dnsmasq tests the address it's about to allocate in
> > case some host is already using it. It sends a ICMP echo request
> > (essentially a ping) and if it gets a reply, the test fails. After a 3
> > second timeout the test succeeds and the address is allocated. If you're
> > happy that there are no machines using IP addresses without leasing
> > them, or that the similar test that DHCP clients do will find this, then
> > you can disable the check in dnsmasq using the --no-oing config flag.
> } you can disable the check in dnsmasq using the --no-ping config flag.

 --no-Ping

Quoting dnsmasq manual page

  -5, --no-ping
         (IPv4  only)  By default, the DHCP server will attempt to ensure
         that an address is not in use before allocating it to a host. It
         does  this  by  sending an ICMP echo request (aka "ping") to the
         address in question. If it gets a reply, then the  address  must
         already be in use, and another is tried. This flag disables this
         check. Use with caution.


The 3 seconds from the subject line explained
and how to avoid that delay.


> Do you think dnsmasq could watch/ping its IP address range while it is
> idle, caching the result? It might examine the local arp table as well:
> If there is an entry with matching MAC and IP address, isn't it reasonable
> to assume that the IP address is not in use somewhere else?


I think that "make dnsmasq a network monitor"
should be in seperate thread.



Regards
Geert Stappers
DevOps engineer