Switching to VoIP

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Chapter 10: Security and Monitoring

telephony apps. That would not be a good situation anywhere: voice is expected to

work 100 percent of the time.

But rather than respond to threats after you’ve already become a victim, you can use

a few techniques to proactively monitor for problems. These techniques are applied

at places where network traffic is concentrated: routers and softPBX servers.

Project 10.3. Logging and Controlling VoIP Packets

with iptables

What you need for this project:

• A Linux PC capable of running the NetFilter firewall (iptables)

• LAN

When a Linux NetFilter firewall is used to protect a group of VoIP bastion hosts or

just as a gateway router for a segment where VoIP is used, a lot of VoIP-related

events can be monitored and logged. Logging from the firewall is useful for the secu-

rity-minded, but it’s important for other reasons, too. It lets you get a feel for which

remote networks and hosts are communicating with your VoIP services and how

often they are. This can improve your understanding of bandwidth consumption and

traffic patterns on your network, besides giving you a keener awareness of security.

NetFilter’s default configuration provides for no logging. If you want a particular

type of packet logged, say, from a specific network or on a specific port, ...