Netgear), although it may not persist on reboot. This may also work on Linux-based routers without an option if you gain command line access (e.g. for automatically opening RTP ports it does not perform ALG and does not modify the packets, and so can safely be left loaded. The nf_conntrack_sip module tracks open connections, e.g. To unload the ALG use the following command: nf_nat_sip contains all the SIP ALG functionality. Iptables has two loadable modules (nf_conntrack_sip and nf_nat_sip) for processing SIP packets. Also, if you know of some devices that cannot disable their built-in SIP ALG please list or link to them there. Please add any devices that you know of in the comment section at the bottom of the page. Disabling ALG įollowing are some specific instructions on how to disable SIP ALG on various consumer– and business–grade routers. That way you won't experience problems if you switch to TLS encrypted calls or need to make configuration changes when switching between unencrypted and encrypted calls. TLS įor encrypted calls you will always need to support NAT traversal on the SIP client itself.Įven if you're only making unencrypted calls using SIP ALG it is far better to get your phone or edge router correctly to handle that NAT on its own for all calls from the very start. Since TLS packets cannot be read nor modified by the router, SIP ALGs will never be able to mangle encrypted calls. The simple solution to this is to use encrypted communications. Also, be mindful of the fact that some manufacturers have created devices whose SIP ALG's cannot be disabled. The following sections contain instructions and links to more information about various devices that have SIP ALG's and how to disable them. Most routers that have SIP ALG's come with them enabled by default, which means that it's up to the user or admin to dig into the configuration to disable them. Brian K West has described them as "evil" - which is not really an understatement if you've ever been burned by one. While ostensibly a SIP ALG is designed to enhance SIP and make the notoriously problematic NAT traversal issues easier to deal with, the simple fact of the matter is that most SIP ALG's are horribly broken. A more complete discussion can be found on WikiPedia and VoIP-info. An ALG (Application Layer Gateway) is a security component, commonly found in a router or firewall device, that is supposed to enhance the ability for certain protocols to traverse NAT.
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