A method for advertising a bit error, comprising: detecting (S301), 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 (S302), 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 (S301), 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 (S302), 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. <EOS>