7.1. ARP Servers and Broadcasts

The Address Resolution Protocol (ARP) described in [11] can, if incorrectly implemented, cause problems when broadcasts are used on a network where not all hosts share an understanding of what a broadcast address is. The temptation exists to modify the ARP server so that it provides the mapping between an IP broadcast address and the hardware broadcast address.

This temptation must be resisted. An ARP server should never respond to a request whose target is a broadcast address. Such a request can only come from a host that does not recognize the broadcast address as such, and so honoring it would almost certainly lead to a forwarding loop. If there are N such hosts on the physical network that do not recognize this address as a broadcast, then a datagram sent with a Time-To-Live of T could potentially give rise to T**N spurious re-broadcasts.