Firewalls

• A device that historically sits at the border between different networks and monitors traffic flowing between them.

• It’s capable of reading packet data and either allowing or denying traffic based on that data.

• Firewalls establish a barrier between networks of different security levels.

• What data a firewall can read and act on depends on the OSI layer the firewall operates on. For example: if it’s a L3 it can read and act towards source and destination IP addresses and ranges. L4 protocol and port numbers, L5 can act as a L4 also but understand response traffic, and L7 application specifics.

Tips from the community:

• Aidan Finn's hub design pattern: put a small diagnostic VM in the hub next to the firewall. If a connection is failing, you can test from that VM to prove quickly whether the firewall is actually the problem, without touching production traffic. Aidan Finn, IT Pro

• Worth knowing as a limitation, not a tip exactly: in a Virtual WAN hub, the hub VNet sits in a Microsoft-managed tenant. You can't get into it to troubleshoot, which means you're at the mercy of Azure support if something's wrong at the hub level. That's not true of a VNet-based hub, where you have full access. Aidan Finn, IT Pro