[Dnsmasq-discuss] DHCP server not assigning IP to RTMU86

[Geert Stappers]

On Mon, May 23, 2022 at 08:37:41PM +0200, Kamil via Dnsmasq-discuss wrote:
> On 20/05/2022 19:19, Simon Kelley <simon at thekelleys.org.uk> wrote:
> >
> > I have a theory:
> >
> > In the logs, it takes between 7 and 9 seconds after carrier detect on
> > eth0 (I guess that's when you plug the RTMU86 in?) before eth0 is
> > allocated IP address 192.168.6.1. Until the address is allocated,
> > dnsmasq will ignore DHCP requests and log
> >
> > "DHCP packet received on eth0 which has no address"
> >
> > If the RTMU86 send a DHCP discover faster than 7 seconds and doesn't
> > retry in a reasonable time, that could explain the problem.
> >
> > ISC dhcpd may not need the local interface to be configured with an IP
> > address, which would explain the different behaviour.
> >
> >
> > The packet capture below shows just one DHCPDISCOVER being sent from
> >   0.0.0.0.bootpc > 255.255.255.255.bootps
> >
> > and it's before the  IP 192.168.6.1 > igmp.mcast.net which markswhen
> > eth0 gets an IP address.
> >
> > If you repeat the same test and leave the capture running for a few
> > minutes, do you see any more  0.0.0.0.bootpc > 255.255.255.255.bootps
> > packets, and if you do, do they get a reply?
> >
> > If I'm right, the solution may be to configure eth0 with a statis IP
> > address, so it doesn't have to wait for dhcpcd to go through a lengthy
> > process to give it an IP address every time the cable gets plugged in.
> >
> >
> Dear Simon,
> 
> 1) I've just sent my reply to Geert where I included my full logs with
> exact timestamps and my comments. Please have a look:
> https://www.mail-archive.com/dnsmasq-discuss@lists.thekelleys.org.uk/msg16249.html

For the record:
  I have seen that posting and choose to go silent about it.


> 2) Because I'm switching between two devices and the address for "Device X"
> is being assigned every time  - I think that it's not the case of "time".
> 3) Also I've left RTMU86 for a little bit longer and as you can see it
> retries several times.
> 4) eth0 has static IP configured for all this time. In /etc/dhcpcd.conf I have:
> | interface eth0
> | static ip_address=192.168.6.1/24
> 
> Kind regards,
> Kamil


Groeten
Geert Stappers
-- 
Some things in life can never be fully appreciated nor understood
unless experienced firsthand. Some things in networking can never be
fully understood by someone who neither builds commercial networking
equipment nor runs an operational network.
                    -- https://datatracker.ietf.org/doc/html/rfc1925