A packet transmission method, implemented by a first network device includes determining a first master logical interface, where the first master logical interface is associated with a first virtual network identifier and a first sub-logical interface, and the first sub-logical interface is associated with a second virtual network identifier, and receiving an advertisement packet from a second network device through the first master logical interface, where the advertisement packet includes the first virtual network identifier, first internet protocol (IP) information associated with the first virtual network identifier, the second virtual network identifier, and second IP information associated with the second virtual network identifier.