I recently received a comment from Gerry Gerofsky about IPv6 network discovery:
Hi Terry, I am trying to understand how CiscoWorks, OpenView discovers an IPv6 network? In Ipv4, typically a tool like OpenView CiscoWorks, you feed it a subnet and it goes and checks all the IP's. What is available in IPv6? In this case, given 2^64 hosts in a subnet, the same sort of scan does not sound logical. This will be a great topic, and I have spent the past day trying to find an answer without avail. Thanks a lot Cheers, Gerry
As you've noted, network discovery in IPv6 doesn't work by using ping sweeps because the address space is simply too large. The key is to identify which devices are likely to know about all or most of its neighbors, such as the default router on the subnet. I've mentioned before that it is a good idea to give each default router (and all network infrastructure devices in a subnet) an address out of a well-known range of addresses, such as <subnet>::1. Network discovery would query this device (via SNMP or CLI or other management mechanism) to query its IPv6 neighbor table, thus finding all the IPv6 neighbors on that subnet.
But what about doing a full network discovery? By starting with a seed router, and learning the IPv6 addresses of routing neighbors, one could build a table of all the routers in the infrastructure and the subnets that they service. Then query each router's IPv6 neighbor table to learn of the IPv6 devices on each subnet.
Another mechanism, which may provide some additional information, is to use a probe to capture flow data, such as source/destination address information as it crosses a key point in the infrastructure. This typically gives you address information about hosts and may be useful in learning of new subnets.
To help with management of the infrastructure, I'd enable CDP/LLDP on all internal interfaces (disable it on externally facing interfaces), so that neighboring infrastructure devices can be more easily discovered. I recommend this for IPv4 as well. While not strictly necessary, it helps speed up the infrastructure discovery process.
-Terry