What is the default authentication in RIPv2 when authentication is enabled?
正解:C
Explanation/Reference: Explanation: Cisco implementation of RIPv2 supports two modes of authentication: plain text authentication and Message Digest 5 (MD5) authentication. Plain text authentication mode is the default setting in every RIPv2 packet, when authentication is enabled. Plain text authentication should not be used when security is an issue, because the unencrypted authentication password is sent in every RIPv2 packet. Reference: https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13719-50.html