On 31/12/2018 21:39, Jon Anderson wrote:
> Hello all,
> 
> I wanted to setup a PiHole for blocking ads and for the ability to
> modify DNS settings network-wide. I have just switched my ISP to AT&T
> fiber where we are required to use a supplied modem/router (ARRIS
> BGW210-700) which does not allow setting DNS servers manually. I was
> happy to find out that I could get around this by moving DHCP services
> to PiHole. I disabled the DHCP on the ARRIS and enabled the service on
> the PiHole. And now every device is using the PiHole for DNS with an
> upstream DNS from Cloudflare instead of AT&T’s slow DNS.
> Everything is working fine.
> When I look at the pihole-log though, I see pages and pages of this:
> 
> Dec 30 05:47:09 dnsmasq-dhcp[598]: DHCPOFFER(eth0) 192.168.1.102
> 88:96:4e:xx:xx:xx
> Dec 30 05:47:10 dnsmasq-dhcp[598]: DHCPDISCOVER(eth0) 88:96:4e:xx:xx:xx
> Dec 30 05:47:10 dnsmasq-dhcp[598]: DHCPOFFER(eth0) 192.168.1.102
> 88:96:4e:xx:xx:xx
> Dec 30 05:47:10 dnsmasq-dhcp[598]: DHCPDISCOVER(eth0) 88:96:4e:xx:xx:xx
> 
> Always the same IP. Always the same MAC address. Always between 1 and 3
> seconds apart.
> I never get anything other than OFFER and DISCOVER. It looks similar to
> the problems
> in 
> https://www.mail-archive.com/dnsmasq-discuss@lists.thekelleys.org.uk/msg03282.html
> and 
> https://www.mail-archive.com/dnsmasq-discuss@lists.thekelleys.org.uk/msg00849.html.
> It does not seem to be the same problem reported by Marc Elbirt only a
> few moments ago, though there are some similarities.
> 
> I did some digging about MAC addresses and found that the MAC address
> can tell you about the manufacturer of the device. I discovered that
> 88:96:4e corresponds to ARRIS. I checked the modem/router on it’s status
> page and found that the MAC addresses for the 2.4Ghz AP, the Guest
> network AP, and the 5Ghz AP are all very similar to the MAC address that
> seems to be having problems.
> So this seems pretty conclusive that the device that will not accept
> it’s IP address is part of the modem/router, but I’m not sure what it is
> or how to get it to accept the 192.168.1.102 or stop requesting an IP
> altogether.
> 

That looks like a client bug: it should at least do exponential back-off.


You could try using dhcp-mac and dhcp-ignore to configure dnsmasq to
just ignore requests from the offending MAc address.

Cheers,

Simon


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