Firewalls and Session Border Controllers

To put it mildly, firewalls and VoIP networks are not best friends. The relationship started out badly when VoIP asked Firewall to allow all UDP ports greater than 1024 through, as if it were a normal request. Firewall was greatly offended, and the two have not talked much since then.

The VoIP and Firewall Problem

While recent changes to VoIP devices have reduced the number of ports needed, several VoIP networks still use a lot of ports on the network, where many of them are not static. For example, the following list shows the possible ports that may be used in a VoIP network:

SIP

TCP/UDP 5060

TCP/UDP 5061

IAX

TCP/UDP 4569

RTP

UDP 1024-65535 (audio/video)

UDP 1024-65535 (control)

H.323

TCP/UDP 1718 (Discovery)

TCP/UDP ...

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