A method for advertising a bit error, comprising: detecting, by an intermediate node on a first tunnel, that a bit error rate of a packet sent through the first tunnel exceeds a threshold; and sending, by the intermediate node, a first packet to an egress node on the first tunnel through the first tunnel, wherein the first packet is used to indicate that a bit error occurs on the first tunnel, the first packet is further used to indicate the egress node to send a second packet to an ingress node on the first tunnel through a second tunnel, wherein the second tunnel is a reverse tunnel of the first tunnel, wherein the first packet comprises a label and a bit error flag, the label is used by the egress node to determine the first tunnel and the second tunnel, and the bit error flag is used to indicate that a bit error occurs on a tunnel through which the first packet is sent; wherein the first packet is a bidirectional forwarding detection BFD packet, the BFD packet comprises a diagnostic field, the diagnostic field is used to carry the bit error flag; and the second packet is a BFD packet, the BFD packet comprises a diagnostic field, the diagnostic field is used to carry a second bit error flag; and wherein the second packet comprises a second label and the second bit error flag, wherein the second label is used by the ingress node to determine the first tunnel, and the second bit error flag is used to indicate that a bit error occurs on the first tunnel, such that after receiving the second packet and determining that a bit error occurs on the first tunnel, the ingress node can send data to the egress node not through the first tunnel but through a backup tunnel, to avoid data traffic loss. detecting, by an intermediate node on a first tunnel, that a bit error rate of a packet sent through the first tunnel exceeds a threshold; and sending, by the intermediate node, a first packet to an egress node on the first tunnel through the first tunnel, wherein the first packet is used to indicate that a bit error occurs on the first tunnel, the first packet is further used to indicate the egress node to send a second packet to an ingress node on the first tunnel through a second tunnel, wherein the second tunnel is a reverse tunnel of the first tunnel, wherein the first packet comprises a label and a bit error flag, the label is used by the egress node to determine the first tunnel and the second tunnel, and the bit error flag is used to indicate that a bit error occurs on a tunnel through which the first packet is sent; wherein the first packet is a bidirectional forwarding detection BFD packet, the BFD packet comprises a diagnostic field, the diagnostic field is used to carry the bit error flag; and the second packet is a BFD packet, the BFD packet comprises a diagnostic field, the diagnostic field is used to carry a second bit error flag; and wherein the second packet comprises a second label and the second bit error flag, wherein the second label is used by the ingress node to determine the first tunnel, and the second bit error flag is used to indicate that a bit error occurs on the first tunnel, such that after receiving the second packet and determining that a bit error occurs on the first tunnel, the ingress node can send data to the egress node not through the first tunnel but through a backup tunnel, to avoid data traffic loss.