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IPv6 address mechanims in NAV

The basis for UNINETT's IPv6 statistics is data collected by NAV (Network Administration Visualized). This document describes the system in use by NAV 3.5 (but being improved in 3.6).

Data structures

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.

Source data

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.

IP-MIB

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, but unfortunately, NAV 3.5 does not support this table.

IPv6-MIB

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-IETF-IP-MIB

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.

Algorithm

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.

IPv6 statistics

Statistics on IPv6 usage are obtained by examining NAVs ARP database table. The number of active IP addresses of each address family (v4, v6) 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.

ipv6.1284113164.txt.gz · Last modified: 2010/09/10 10:06 by faltin