One of the security factors I’ve heard espoused about IPv6 is that the large address space (128 bits: 64 bits of network and 64 bits of host address) makes it impossible to scan the network for hosts. On initial inspection, this seemed like a reasonable thought.
However, when you look at IPv6’s use of multicast for router and route prefix discovery, the security advantage doesn’t make as much sense. Nothing prevents a system from monitoring the multicast address and collecting information about other systems on the local subnet. Since the networks of small companies and home networks are typically a single subnet, this approach works well for finding other local systems.
But what about remote subnets? Doesn’t the large address space help reduce scanning there? It sure does. However, it doesn’t inhibit the exploitation of peer relationships. Think of the addresses of the application servers known by the end stations on your network. Another source is the IP addresses contained in email headers. Overall, I see that there is still a reasonably rich set of address data that can be harvested through other mechanisms.
I predict that the black hat community will quickly find these and other sources of addresses to replace address space scanning techniques. Defense in depth is the only viable recourse.
Re-posted with Permission
NetCraftsmen would like to acknowledge Infoblox for their permission to re-post this article which originally appeared in the Applied Infrastructure blog under http://www.infoblox.com/en/communities/blogs.html