I did a session at SharkFest’18 Europe in Vienna with the title of “Crash Course: IPv6 and Network Protocols“. Since the presentation slides + audio were recorded you can listen to the talk, too. Here are some notes about the motivation for this session as well as feedback from the attendees.
I am still a bit confused about the different switch types a FortiGate firewall is able to handle. While there is a lot of information on the Internet about the “internal-switch-mode” of “switch/interface“, I have not found any good information about the differences between the “Hardware/Software/VLAN” switch types that are configured via the GUI or via the “virtual-switch-vlan enable” CLI command. Though I still don’t know exactly all differences, I am trying to explain some of them here.
In the legacy 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. The mapping of “identity to IP” is not done automatically somewhere.
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.
The Multi Router Traffic Grapher (MRTG) can, of course, not only monitor routers via SNMP, but any devices that support the Simple Network Management Protocol, e.g., switches. With the tool “cfgmaker” it is quite easy to add switches with many ports to the monitoring system. However, some subsequent work is needed to have a clean configuration. This blog post presents a step-by-step guide for adding a switch into MRTG/Routers2.