Securing VoIP networks
The Network
Experts agree that one important step in the quest for VoIP security is to separate the VoIP network from the ordinary LAN traffic. The complex and relative insecure nature of computer networks adds many opportunities for eavesdropping and other forms of attack, and seasoned admins are well aware that physical access is more or less identical to a hacked system.
To isolate the VoIP network, use physical separation or even a virtual LAN (VLAN) configuration. Of course, separating VoIP traffic will not protect you against physical access by an attacker who connects to a free port of the voice network. (If a port is accessible, the attacker can simply hitch up a laptop and spoof a phone's MAC address.) The best way to combat this kind of local intrusion is to use additional 802.1x [15] [16] authentication against the switch.
To ensure secure VoIP communications with the enterprise system for road warriors, it makes sense to route the connection via a VPN tunnel. This setup should support low-bandwidth codecs, such as GSM (Global System for Mobile communications) [17]. As an alternative, you might prefer to use SRTP and SIPS--S/MIME, if clients and servers support this option, because of the lower protocol overhead.
Figure 5 shows a combination of the techniques discussed in this article in which the VoIP infrastructure is isolated from the remaining system. The link between the sub-branch and head office uses one or multiple VPN tunnels. (When forecasting the bandwidth, it is important to take the VPN protocol overhead into consideration.) The PSTN (Public Switched Telephone Network) connection can be handled separately at each branch or routed via the head office. A failover link for each branch is a good idea. This keeps your branch offices reachable, even if the IP connection fails or is overloaded.
Conclusion
If you are thinking about adding a voice component to your network presence, it makes sense to plan your approach to VoIP security before you begin. The hardware and software tools of the VoIP environment provide a number of interesting security options. First determine which protocols and components you need for your VoIP network, then shop for tools that provide the necessary support. Table 1 shows the results of our research into the compatibility of phones and VoIP appliances by various manufacturers.
If you already have a VoIP network, simple techniques such as VLAN isolation and strategic use of available encryption alternatives will help you build a better and more secure environment for VoIP communications.
Infos
- SIP standard, RFC 3261: http://www.ietf.org/rfc/rfc3261.txt
- SDP standard, RFC 4566: http://www.rfc-editor.org/rfc/rfc4566.txt
- RTP reference: http://www.voip-info.org/wiki-RTP
- SIP, SDP, RTP, and NAT: http://swik.net/SIP/del.icio.us+tag%2FSIP/Intruduction+to+SIP%2FSDP%2FRTP+and+NAT/bd1m0
- SIP security: http://www.cisco.com/en/US/docs/ios/12_3/vvf_c/cisco_ios_sip_security_application_guide/sipsecov.html
- TLS: http://en.wikipedia.org/wiki/Transport_Layer_Security
- S/MIME: http://en.wikipedia.org/wiki/S/MIME
- Secure RTP: http://en.wikipedia.org/wiki/Secure_Real-time_Transport_Protocol
- SIP, RFC 3893: http://www.ietf.org/rfc/rfc3893.txt
- RTP, RFC 3550: http://www.ietf.org/rfc/rfc3550.txt
- MIKEY, RFC 3830: http://www.ietf.org/rfc/rfc3830.txt
- ZRTP: http://zfoneproject.com/zrtp_ietf.html
- Skype survey: http://www.anagram.com/berson/skyeval.pdf
- The TLS protocol, RFC 4346: http://www.ietf.org/rfc/rfc4346.txt
- 802.1x authentication standard: http://en.wikipedia.org/wiki/802.1x
- 802.1x and attackers on the same port: http://searchsecurity.techtarget.com/expert/KnowledgebaseAnswer/0,289625,sid14_gci1268965,0.html
- GSM communications: http://en.wikipedia.org/wiki/Global_System_for_Mobile_Communications
« Previous 1 2
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Find SysAdmin Jobs
News
-
OpenMandriva Lx 23.03 Rolling Release is Now Available
OpenMandriva "ROME" is the latest point update for the rolling release Linux distribution and offers the latest updates for a number of important applications and tools.
-
CarbonOS: A New Linux Distro with a Focus on User Experience
CarbonOS is a brand new, built-from-scratch Linux distribution that uses the Gnome desktop and has a special feature that makes it appealing to all types of users.
-
Kubuntu Focus Announces XE Gen 2 Linux Laptop
Another Kubuntu-based laptop has arrived to be your next ultra-portable powerhouse with a Linux heart.
-
MNT Seeks Financial Backing for New Seven-Inch Linux Laptop
MNT Pocket Reform is a tiny laptop that is modular, upgradable, recyclable, reusable, and ships with Debian Linux.
-
Ubuntu Flatpak Remix Adds Flatpak Support Preinstalled
If you're looking for a version of Ubuntu that includes Flatpak support out of the box, there's one clear option.
-
Gnome 44 Release Candidate Now Available
The Gnome 44 release candidate has officially arrived and adds a few changes into the mix.
-
Flathub Vying to Become the Standard Linux App Store
If the Flathub team has any say in the matter, their product will become the default tool for installing Linux apps in 2023.
-
Debian 12 to Ship with KDE Plasma 5.27
The Debian development team has shifted to the latest version of KDE for their testing branch.
-
Planet Computers Launches ARM-based Linux Desktop PCs
The firm that originally released a line of mobile keyboards has taken a different direction and has developed a new line of out-of-the-box mini Linux desktop computers.
-
Ubuntu No Longer Shipping with Flatpak
In a move that probably won’t come as a shock to many, Ubuntu and all of its official spins will no longer ship with Flatpak installed.