This application discloses a packet transmission method and apparatus, to help trace a source router generating a routing information update packet, so as to improve network maintenance efficiency and shorten failure duration. The method includes: generating, by a first router, a first routing information update packet; generating, by the first router, a first source-tracing packet, where the first source-tracing packet is used to indicate that the first router is a source router generating the first routing information update 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 to the second router.