A packet transmission method, wherein the method comprises: generating, by a first router, a first routing information update packet, wherein the first routing information update packet is a link-state advertisement, LSA, packet or a link state packet, LSP, packet; characterized in that the method further comprises: generating, by the first router, a first source-tracing packet, wherein the first source-tracing packet is used to indicate that the first router is a source router generating the first routing information update packet, wherein the first source-tracing packet includes first information and second information, wherein the first information includes at least one of a router identifier of the first router, a name of the first router, or an Internet Protocol, IP, address of the first router, and the second information includes at least one of an identification, ID, of the LSA packet, a sequence number of the LSA packet, an ID of the LSP packet or a sequence number of the LSP packet; and determining, by the first router, that a second router adjacent to the first router has a source-tracing capability, and sending the first source-tracing packet and the first routing information update packet to the second router, wherein the determining comprises: sending, by the first router, a first source-tracing capability negotiation packet to the second router, wherein the first source-tracing capability negotiation packet is used to query whether the second router has the source-tracing capability; after receiving a first source-tracing capability acknowledgement packet sent by the second router, determining, by the first router, that the second router has the source-tracing capability, wherein the first source-tracing capability acknowledgement packet is used to indicate that the second router has the source-tracing capability. generating, by a first router, a first routing information update packet, wherein the first routing information update packet is a link-state advertisement, LSA, packet or a link state packet, LSP, packet; characterized in that the method further comprises: generating, by the first router, a first source-tracing packet, wherein the first source-tracing packet is used to indicate that the first router is a source router generating the first routing information update packet, wherein the first source-tracing packet includes first information and second information, wherein the first information includes at least one of a router identifier of the first router, a name of the first router, or an Internet Protocol, IP, address of the first router, and the second information includes at least one of an identification, ID, of the LSA packet, a sequence number of the LSA packet, an ID of the LSP packet or a sequence number of the LSP packet; and determining, by the first router, that a second router adjacent to the first router has a source-tracing capability, and sending the first source-tracing packet and the first routing information update packet to the second router, wherein the determining comprises: sending, by the first router, a first source-tracing capability negotiation packet to the second router, wherein the first source-tracing capability negotiation packet is used to query whether the second router has the source-tracing capability; after receiving a first source-tracing capability acknowledgement packet sent by the second router, determining, by the first router, that the second router has the source-tracing capability, wherein the first source-tracing capability acknowledgement packet is used to indicate that the second router has the source-tracing capability. sending, by the first router, a first source-tracing capability negotiation packet to the second router, wherein the first source-tracing capability negotiation packet is used to query whether the second router has the source-tracing capability; after receiving a first source-tracing capability acknowledgement packet sent by the second router, determining, by the first router, that the second router has the source-tracing capability, wherein the first source-tracing capability acknowledgement packet is used to indicate that the second router has the source-tracing capability.