For those of you that don't know, SIP ALG is a feature often enabled in routers to prevent some of the problems that can be caused by Network Address Translation (NAT) and Firewall functions interfering with the SIP traffic. This can be particularly problematic for VoIP calls, causing phone registrations, inbound calls and call transfers to fail. Currently, many routers are shipped with SIP ALG enabled as default with very little straight forward guidance to disable this feature.
The NICC guidance recommends:
- SIP ALGs being be disabled by default
- SIP ALGs being easily configurable (i.e. to be disabled/enabled) by end users as part of the normal administration of the equipment
- Configuration status displays should clearly indicate that a SIP ALG is either disabled or enabled
I for one welcome this formal guidance and the next steps will be to educate the industry and particularly router manufacturers to consider this guidance when developing new products.
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