IPv6 address mechanims in NAV

UNINETT has made available statistics on the number of IPv6-active hosts in the Norwegian universities and university colleges. The statistics are available online. The basis for the statistics is data collected by NAV (Network Administration Visualized).

NAV keeps track of mappings between host IP addresses and ethernet MAC addresses in a database table known as the Arp table. Each Arp table record contains a source router id, an IP address (v4 or v6), a MAC address, a start time and an end time.

The start time denotes the first time NAV saw this active mapping on a router. The end time denotes the first time after the start time that NAV no longer saw this mapping at the same router. An end time value of 'infinity' denotes an “open” record: A mapping that is still active.

NAV's source for IP/MAC mapping data are routers' IPv4 ARP caches and IPv6 Neighbor caches. These are collected via SNMP through various MIBs.

First defined in RFC 1213, later revised in RFC 4293.

IPv4 address mappings are collected from ipNetToMediaTable. This table has been deprecated in the revised IP-MIB. The revised MIB contains ipNetToPhysicalTable, which maps both IPv4 and IPv6 addresses. ( NAV versions prior to 3.6 did not support the revised table)

Defined as a working draft by the IETF IPv6 Working Group, but later deprecated. Still in use by several vendors, though.

IPv6 address mappings are collected from ipv6NetToMediaTable.

Cisco proprietary MIB based on a draft version of the revised IETF IP-MIB (finally published in RFC 4293).

IPv6 address mappings are collected from cInetNetToMediaTable.

After collecting all mappings from a router, NAV will iterate through each mapping. If an identical mapping is found to be “open” in the database Arp table, it does nothing. Otherwise, it will add a new Arp record to the database, using the current time as the start time.

NAV will then iterate over all “open” mappings from the database Arp table that were not found among the current mappings on the router, and “close” these records by setting their ending timestamps to the current time.

Statistics on IPv6 usage are obtained by examining NAVs ARP database table. The number of active IP addresses of each address family (v4, v6), and the number of unique MAC addresses in use at any given time can be extracted from this table and used to create aggregate statistics across a number of NAV installations in the Norwegian NREN. The numbers in UNINETT's published graphs count the number of unique MAC addresses seen, so users employing IPv6 privacy extensions should only be counted once per institution.

The IPv6 data is of course utilized several places in NAV, in particular in the Machine tracker where a NAV user can track the whereabouts of IPv6 and IPv4 addresses.

If you would like to implement your own solution for IPv6 deployment statistics, easiest way to go is first to install NAV. Alternatively you could implement your own IPv6 SNMP collection scheme based on the ipv6NetToMediaTable. For code details, please contact the NAV team at our mailinglists.