The unused wall socket
In a meeting room a wall socket is live. A visitor plugs in a laptop. It asks for an address and an unknown server answers first.
Nothing was hacked from outside. The weak points were inside: a socket nobody turned off and a setting nobody switched on.
Today you learn six weak points in how a system is built, and how each is controlled.
Key words
| Word | What it means |
|---|---|
| Network | Computers and devices linked so they can share data. |
| DHCP | The service that gives each device on a network its address when it joins. |
| DHCP snooping | A switch setting that only trusts DHCP answers from approved ports. |
| VLAN | Virtual LAN: a group of switch ports that act as their own separate network. |
| VLAN hopping | An attack where a device gets into a VLAN it should not be in. |
| ACL | Access control list: an ordered list of rules saying which traffic is allowed or blocked. |
| Firewall | A gate that lets some traffic in or out and blocks the rest. |
| Port | A numbered door on a computer, used by one kind of service. |
| Topology | The layout of a network: how its devices are joined. |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can name six weak points in network design and give the controls for each.
Starter: the earlier weak points
Have a go
Starter: the earlier weak points
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Weak point 1: DHCP spoofing
When a device joins a network, DHCP gives it an address and tells it where the gateway is. A rogue DHCP server answers first with false details. The device then sends its traffic through the attacker.
Control: DHCP snooping. The switch trusts DHCP answers only from the ports where the real server sits, and drops answers from every other port.
Weak point 2: VLAN attacks and hopping
A VLAN keeps groups apart. A badly set-up switch port can be tricked into acting as a trunk, or can accept frames meant to slip into another VLAN. This is VLAN hopping. The attacker reaches a VLAN they should not.
Controls: test the VLAN set-up after building it, and on a schedule. Monitor the network for odd traffic between VLANs. Turn off automatic trunking, and shut unused ports.
Check: DHCP and VLANs
Have a go
Check: DHCP and VLANs
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.