A security authentication method includes: receiving, by a control plane of a BFD device, a first BFD packet that is sent by a control plane of a peer BFD device; generating, by the control plane, a first token value according to the random nonce; sending the first token value to a data plane; receiving, by the data plane, a second BFD packet that is sent by a data plane of the peer BFD device, where the second BFD packet carries authentication information, and the authentication information includes a random nonce; and generating, by the data plane, a second token value according to the random nonce included in the authentication information and by using a calculation method the same as that of the control plane, and successfully authenticating, by the data plane, the second BFD packet if the first token value and the second token value are the same.