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
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you've found an article to be beneficial.
News
-
elementary OS 7.1 Now Available for Download
The team behind elementary OS has released the latest version of its operating system with a focus on personalization, inclusivity, accessibility, and privacy.
-
The GNU Project Celebrates Its 40th Birthday
September 27 marks the 40th anniversary of the GNU Project, and it was celebrated with a hacker meeting in Biel/Bienne, Switzerland.
-
Linux Kernel Reducing Long-Term Support
LTS support for the Linux kernel is about to undergo some serious changes that will have a considerable impact on the future.
-
Fedora 39 Beta Now Available for Testing
For fans and users of Fedora Linux, the first beta of release 39 is now available, which is a minor upgrade but does include GNOME 45.
-
Fedora Linux 40 to Drop X11 for KDE Plasma
When Fedora 40 arrives in 2024, there will be a few big changes coming, especially for the KDE Plasma option.
-
Real-Time Ubuntu Available in AWS Marketplace
Anyone looking for a Linux distribution for real-time processing could do a whole lot worse than Real-Time Ubuntu.
-
KSMBD Finally Reaches a Stable State
For those who've been looking forward to the first release of KSMBD, after two years it's no longer considered experimental.
-
Nitrux 3.0.0 Has Been Released
The latest version of Nitrux brings plenty of innovation and fresh apps to the table.
-
Linux From Scratch 12.0 Now Available
If you're looking to roll your own Linux distribution, the latest version of Linux From Scratch is now available with plenty of updates.
-
Linux Kernel 6.5 Has Been Released
The newest Linux kernel, version 6.5, now includes initial support for two very exciting features.