On the MSR router, I hope to adjust the Keepalive packet time of the HDLC protocol to 20 seconds. The correct configuration is ______.

During system startup, type ______ according to the prompt, the system will interrupt booting and enter BootROM mode.

In the OSI reference model, the function of the network layer is mainly ______.

After the DHCP client receives the DHCP ACK message, if it finds that the IP address it will use already exists on the network, what message will it send to the DHCP server?

A large financial network needs to use multiple WAN protocols and routing protocols. To enhance network security, it is hoped that the selected protocol has security measures such as authentication, encryption, and access control.
Then when choosing the WAN protocol and routing protocol, which of the following protocols may meet the requirements? (multiple choice)