On 4/19/23 11:38, Buck Horn wrote:
Yes this is proxy ARP in https://en.wikipedia.org/wiki/Proxy_ARP.
HostAPd has an option called proxy_arp which setups up proxy_arp with
additional requirements to meet the Hotspot 2.0 standards. It comes
built in with a couple of snoopers, including a DHCP snooper to
configure proxy_arp without the need for additional software.
I've attached a pcap file, if you need any more logs or information
please let me know. Only thing I've changed for this capture is
setting the lease time to 2m in order to make it faster for me to
capture this for you, in normal operation it was set to 8hours.
Note that the capture includes a ARP probe from the ESP and no
response, just keep in mind that the WiFi router does in fact respond
to it, it just doesn't do so over that bridge port so it didn't get
captured on the gateway's end.
I think your issue starts earlier:
Your pcap indicates a failing lease renewal.
Lines 12 to 18 show your ESP is attempting to renew its DHCP lease
through 10.46.109.1 after ~62 seconds as expected (about half the
120secs leasetime) - but those requests seem to never have received a
reply.
In absence of a reply from the known DHCP server, lines 19 to 27 then
show your ESP to send renewal requests to the broadcast address.
As those are not answered either, your ESP finally releases its
expired lease (line 28).
It then initiates DHCP negotiation for a completely new lease, by
broadcasting for DHCP servers, and it's only then that ARP probing
would prompt it to DHCPDECLINE.
But I'd have expected dnsmasq to have extended your ESP's existing
lease straight for the first DHCPREQUEST for renewal (line 12).
This would suggest that dnsmasq has not received or ignored both those
DHCPREQUESTs for renewal as well as the DHCPRELEASE, which could
explain both the failed renewal as well as the offending DHCPDECLINEs.
Are you splitting your network, e.g. into several VLANs?
It would be interesting to see what dnsmasq has been logging for that
exchange, to verify whether and how dnsmasq would have received those
DHCPREQUESTs for renewal.
Kind regards,
Buck
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Some good news, it turns out my firewall was dropping any incoming DHCP
message that was not a broadcast (only 255.255.255.255 was getting in)
causing this problem.
You could consider this problem solved.
Sorry for all the noise and concern for nothing.
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