Description:
SIP ALG (Application Layer Gateway) is a feature which is enabled by default in most Cisco routers running Cisco IOS software and inspects VoIP traffic as it passes through and modifies the messages on-the-fly.
For our Hosted VoIP service, including out Single User services, SIP ALG must be disabled on your Cisco router.
This article provides general guidance which should be applicable to nearly all Cisco routers running Cisco IOS, such as the Cisco ISR an ASR series routers.