ARP is essential in an IPv4 network, but what happens in an IPv6 network? IPv6 doesn't use ARP. ARP is replaced with the NDP, which resolves an IP address to a MAC address. 

To see an example of the NDP, go to http://packetlife.net/captures/protocol/icmpv6/ and open the file in Wireshark. As shown in the following screenshot, the first packet in the IPv6_NDP.pcap trace file is a Neighbor Solicitation (NS), followed by a neighbor advertisement:

An NS has the same purpose as an ARP broadcast; however, IPv6 doesn't use broadcasts. It uses Internet Control Message Protocol Version 6 (ICMPv6) with a solicited-node multicast address message that is directed to a specific host. As a result, if you are doing an analysis on a network that only uses IPv6, you may only see a few ARP broadcasts, if any. 

As we can now understand, ARP is a common protocol that you will most likely see while doing analysis, as IPv4 is still widely used. So that you better understand a standard ARP request and reply, the following section provides an overview of an ARP header and the field values.