Tag Archives: IPv6 Duplicate Address Detection

IPv6 Address Statistics based on DAD Messages featured image

IPv6 Address Statistics based on DAD Messages

After my Tcpdump script for storing MAC-IPv6 address bindings via the Duplicate Address Detection messages (link) and an analysis of the realibility of them (here), I had the idea of a Linux script that analyzes the Tcpdump output for obtaining some IPv6 address statistics. It should not show concrete bindings between MAC- and IPv6-addresses, but the number of different kind of IPv6 addresses, such as link-local or global-unicast addresses, built with or without EUI-64, etc.

In the following, I will present my script and will show the results after running it through the DAD logs of a whole month (March 2014) in a BYOD-WLAN with more than 100 clients.

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Reliability of IPv6 DAD Message Sniffing featured image

Reliability of IPv6 DAD Message Sniffing

A few weeks ago I published an article in which I proposed a method on how to capture the MAC- to IPv6-address bindings via sniffing and storing IPv6 DAD messages. Though any IPv6 node MUST send these Duplicate Address Detection messages prior to assign the address, I was not fully assured that *really* each new IPv6 address is stored with this Tcpdump sniffer.

That is, over a whole month I captured the DAD messages on a test BYOD-LAN and furthermore the complete IPv6 connection logs of the corresponding firewall. At best, I should have any IPv6 address that made an outbound connection through the firewall in the DAD logfiles. Here are the results:

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MAC-IPv6-Bindings

Monitoring MAC-IPv6 Address Bindings

In the IPv4 world, the DHCP server allocates IPv4 addresses and thereby stores the MAC addresses of the clients. In the IPv6 world, if SLAAC (autoconfiguration) is used, no network or security device per se stores the binding between the MAC (layer 2) and the IPv6 (layer 3) addresses from the clients. That is, a subsequent analysis of network behaviour corresponding to concrete IPv6 addresses and their client machines is not possible anymore.

A simple way to overcome this issue is to install a service that captures Duplicate Address Detection (DAD) messages from all clients on the subnet in order to store the bindings of MAC and IPv6 addresses. This can be done with a small Tcpdump script on a dedicated Ethernet interface of a Linux host.

In this blog post I will present a use case for storing these bindings, the concept of the DAD messages, a Tcpdump script for doing this job, and the disadvantages and alternatives of this method.

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