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In FortiOS versions up to v6.4, by default and regardless of the firewall policy inspection mode, SIP traffic was proxied by SIP ALG. This can be determined with the following settings:
config system settings
set default-voip-alg-mode proxy-based * | kernel-helper-based
end
The default setting was proxy-based.
Since v7.0.0, a new feature named Flow-Based SIP was introduced.
The particular feature brings optimization to CPU and memory because the VoIP traffic could now be inspected by the IPS engine itself.
However, the original SIP ALG has much more advanced capabilities for VoIP inspection.
After upgrading to v7.0.1+ or v7.2, Flow-Based SIP will now run by default in a firewall policy, which is configured as flow inspection mode.
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Pre-7.0 Config
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After upgrade to 7.0.0
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After upgrade to 7.0.1+
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default-voip-alg-mode kernel
config firewall policy
voip-profile <profile>
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode flow
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inspection-mode proxy
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inspection-mode proxy
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default-voip-alg-mode kernel
config firewall policy
voip-profile none
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode flow
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inspection-mode flow
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inspection-mode flow
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default-voip-alg-mode proxy
config firewall policy
voip-profile <profile>
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode flow
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inspection-mode proxy
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inspection-mode proxy
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default-voip-alg-mode proxy
config firewall policy
voip-profile none
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode proxy
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inspection-mode flow
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inspection-mode proxy
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inspection-mode flow
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For example, a FortiGate was configured in v6.4 as:
config system settings
set default-voip-alg-mode proxy-based
end
config firewall policy
edit 1
set name "VoIP_Policy"
set srcintf "internal1"
set dstintf "wan1"
set srcaddr "all"
set dstaddr "all"
set action accept
set inspection-mode flow <<<<
set schedule "always"
set service "SIP"
set nat enable
end
After upgrading to v7.0.1+ or v7.2, if the goal is to maintain the same behavior as v6.4, the inspection mode of the firewall policy should be configured as proxy-based.
config firewall policy
edit 1
set name "VoIP_Policy"
set srcintf "internal1"
set dstintf "wan1"
set srcaddr "all"
set dstaddr "all"
set action accept
set inspection-mode proxy <<<<
set schedule "always"
set service "SIP"
set nat enable
end
For firewall policies that were originally configured [in v6.4] with a VoIP profile attached to them, they will automatically be switched to proxy inspection during the upgrade process.
Related article:
Technical Tip: SIP traffic and inspection mode in FortiOS 7.x (proxy / flow).
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