The format of an RARP packet is almost identical to an ARP packet (Figure 4.3). The only differences are that the frame type is 0 —8035 for an RARP request or reply, and the op field has a value of 3 for an RARP request and 4 for an RARP reply.
As with ARP, the RARP request is broadcast and the RARP reply is normally unicast.