CPU usage becomes high after DNS mapping is configured


Q: It is recommended that you run the display port-mapping command to query occupied interfaces before configuring the NAT server. You can select an idle interface.

A: After DNS mapping is configured, the CPU processes packets before the router forwards the packets. If a large number of packets need to be processed, the CPU usage is high.
If the CPU usage remains high and affects device usage, it is recommended that you delete the DNS mapping configuration and disable the DNS ALG function to prevent packets from being sent to the CPU, reducing the CPU usage. To protect the router and meet users' service demands, add the NAT server configuration on the interface connected to the internal network.
When an internal network host accesses an internal network server using the domain name, the host sends a domain name request to the DNS server. The DNS server encapsulates the public IP address corresponding to the domain name into the response packet. If the DNS mapping and ALG functions are enabled, the router converts the public IP address that is encapsulated in a DNS response packet into a private IP address when forwarding the packet to an internal network host. After the DNS mapping and ALG configurations are deleted, the router cannot perform IP address translation. You can add the NAT server configuration on the interface connected to the internal network. The public IP address then can be converted into the private IP address of the internal network server, allowing internal network hosts to access the internal network server.

Other related questions:
After a query operation, the CPU usage is high
When you log in to an S series switch (except the S1700) through Telnet from a host, the switch and the host need to exchange packets if you perform any operations. The CPU of the switch processes TCP packets received from the host, and encapsulates related information into TCP packets to send to the host. The query operation requires a large amount of data, and the CPU of the switch receives and sends packets frequently. Therefore, the CPU usage is high after the query operation.

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