Routers that implement ARP MUST be compliant and SHOULD be unconditionally compliant with the requirements in [INTRO:2].
The link layer MUST NOT report a Destination Unreachable error to IP solely because there is no ARP cache entry for a destination; it SHOULD queue up to a small number of datagrams breifly while performing the ARP request/reply sequence, and reply that the destination is unreachable to one of the queued datagrams only when this proves fruitless.
A router MUST not believe any ARP reply that claims that the Link Layer address of another host or router is a broadcast or multicast address.