4. ICMP Extension

4. ICMP Extension

In the case of either a single public IPv4 address (the IPv4 interface address or loopback address of the translator) or a pool of public IPv4 addresses, the translator SHOULD implement the ICMP extension defined by [RFC5837]. The ICMP message SHOULD include the Interface IP Address Sub-Object and specify the source IPv6 addresses of the original ICMPv6. When an enhanced traceroute application is used, it can derive the real IPv6 source addresses that generated the ICMPv6 messages. Therefore, it would be able improve on visibility towards the origin rather than simply blackholing at or beyond the translator. In the future, a new ICMP extension whose presence indicates that the packet has been translated and that the source address belongs to the translator, not the originating node, can also be considered.