SIP users fail to be registered after outbound NAT is configured and canceled on the public network interface of the AR

Q: SIP users fail to be registered after outbound NAT is configured and canceled on the public network interface of the AR.
A: SIP users connect to the SIP server through the AR enabled with outbound NAT. The ALG function is disabled for SIP, so STP packets cannot traverse the NAT device. As a result, the SIP server cannot communicate with SIP users and SIP users fail to be registered.

When registration request packets of SIP users pass through the AR, the AR generates NAT session entries to record packet information and updates entries and the aging time after new packets are received. After the aging time is reached, the NAT session entries that fail to be updated are automatically cleared. Therefore, the SIP users that fail to be registered continue to send registration request packets. NAT session entries cannot be directly cleared after outbound NAT is canceled, and are automatically cleared after the aging time is reached. Because SIP users continuously send registration request packets, the AR continuously update NAT session entries and theaging time. That is, the NAT session entries cannot be automatically cleared. As a result, the SIP users fail to be registered.

Run the nat alg command to enable ALG for SIP so that the SIP server can communicate with SIP users after outbound NAT is configured. In addition, run the reset nat session all command to forcibly clear the NAT session entries and quickly change the NAT configuration. Or, you can run the reset nat session all command to forcibly clear NAT session entries after outbound NAT is canceled, so that the SIP server can communicate with SIP users.

Note: Deleting NAT mapping entries may affect exchange of some packets.

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