Enabling SIP on Fortinet devices
Yesterday (08/08/2013) I came across an issue whereby a set of users had migrated from a standard DSL connection to a VLAN within our corporate network, which resulted in a strange issue with their VoIP phones. After the migration was complete the users were able to place calls successfully BUT when receiving calls the users were able to hear to the caller but the caller was unable to hear the receiver. the caller would hear the call ringing then being collected, at this point the line would then seem as if it was dead. After a bit of investigation it appeared that inbound voice traffic was being blocked for some reason. The Cause The cause of this issue appears to be a session-helper which is enabled by default on Fortinet devices. We tested on two Fortinet devices and the issue was replicated over both Fortinet models. The devices tested where: Fortigate 20c ADSL router Fortigate 300c Firewall The Permanent Fix To resolve the issue we had to complet...