Because this is a default setting, no indication of it being 'on' or 'off' is visible in the configuration. I have SIP inspection enabled and don't see any issues with it and I gain the benefit of not only being able to do a show SIP but the necessary pinholes are dynamically created instead of opening wide static holes these providers often request, but the providers still insist having ALG creates more problems. Cisco (non-ASA) On Cisco devices, SIP-ALG is referred to as SIP Fixup and is enabled by default on both routers and Pix devices. Our ASA is configured with default SIP-inspection settings. So the media never returns from the SIP-trunk after the call is established, because the SDP is the private IP-adress of the MX/MGU. SDP/Return Adress: Internal IP back to MX/MGU. An application-layer gateway (ALG) is used with NAT to translate the SIP or. 200-OK from internal MX/MGU to external SIP: Header IP: Correctly NATed IP back to the MX/MGU. Once authenticated, move into enable mode by typing enable. Log into the ASA through SSH, telnet or the console. Some service providers will recommend disabling this feature. How is SIP not broken after leaving the firewall over the public Internet when being NAT'd from a private to public address if the SIP payload contains a private address that inspection would normally fixup - using the older inspection terminology there -) ? Is STUN or TURN the only way preventing this breakage and can I assume that these providers support that or does that have to be confirmed? Is it not better to have inspection? I know that certain SIP implementations don't add addressing in the application layer, but in the these cases they do. The NAT TCP SIP ALG Support feature allows embedded messages of the Session Initiation Protocol (SIP) passing through a device that is configured with Network Address Translation (NAT) to be translated and encoded back to the packet. Most ASAs will have the inspect sip statement listed in the default policy-map. After talking to a few hosted VoIP providers, they all state that "ALG" or SIP inspection in the case of the Cisco firewall should be disabled. For information about how to configure logging, SNMP, and NetFlow, see the Cisco ASA 5500 Series.
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