How does DHCP Server "Ping IP when allocating new IP" work?

schung2 — Wed, 16 Jan 2013 14:59:33 GMT

What's the destination MAC address when this ping is sent?

When is this ping sent? After/Before DHCP requests?

Thanks.

Re: How does DHCP Server "Ping IP when allocating new IP" work?

mikand — Wed, 16 Jan 2013 22:31:47 GMT

Just guessing here but:

1) ARP-WHOHAS is sent... (unless its reachable through some nexthop because then the 2) below is sent to this nexthop).

2) If someone replies to above (could be some proxyarp or so) an icmp echo request is sent to the mac (unless its routed through some nexthop).

3) If echo reply (or administratively prohibited) is returned the box assumes this ip is already taken.

Someone from PA who could confirm? 🙂

The downside would be if you have a personal/desktop firewall who blocks incoming echo requests...