dhcpcd-discuss

(Reviving old thread for the archives)

On Thu, 15 Jun 2017, RJ Ascani wrote:

> I'm running into an issue whereby dhcpcd declines a valid IP address from the dhcp server because of a well timed ARP probe from our Cisco switch with a source IP of INADDR_ANY. Our Cisco switch has IP Device Tracking<http://www.cisco.com/c/en/us/support/docs/ip/address-resolution-protocol-arp/118630-technote-ipdt-00.html> enabled, which is sending ARP probes with a SIP of 0.0.0.0 to all devices every 30 seconds. In the below log, you can see that after dhcpcd gets the offer and starts probing, it encounters a conflict with hardware address ac:7e:8a:18:ef:90 (the Cisco switch).

> Jun 15 15:32:52 eth0: hardware address ac:7e:8a:18:ef:90 claims 172.18.1.127

We have observed dhcpcd (6.11.5-1rpt7 for Raspberry PI) reporting ARP conflicts
when the Cisco IP Device Tracking is used even with a fully static dhcpcd configuration.

From a little sniffing we have done it seem that although Cisco IP Device Tracking
ARP probes are being sent with the source IP of 0.0.0.0, they are sent via Ethernet
unicast to our device's MAC address and not broadcast, so maybe we can ignore them this
way?

Neither static ifconfig on Linux nor static IP configuration on FreeBSD generates
false positive ARP warnings in this case, maybe dhcpcd is a bit overzealous here?

Marcin

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