In the previous installment of our series of IPv6 posts, we covered some common myths regarding IPv6. In this post, we’ll talk about how the role of ICMP has changed in IPv6 compared to IPv4.
In IPv4, ICMP provides error reporting, flow control and first-hop gateway redirection. This functionality, which is also available in IPv6, is usually not essential to the operation of your network. With IPv6, however, ICMP has gained a much more significant and essential role because of new functionality that is now performed through ICMP. Fragmentation, Neighbor Discovery, and StateLess Address AutoConfiguration (SLAAC) represent essential functionality which is now performed using ICMP messages. Furthermore, many ICMP messages are designed to be sent to multicast addresses instead of only unicast addresses. Therefore, ICMP in IPv6 gains a whole new importance along with a new set of security concerns.