This application provides a method for updating a route in a network, a network device, and a system. A first network device sets up a correspondence between an IP network segment and a first IP address, where the first IP address is an IP address of the first network device. The first network device sends a first LSA packet to a third network device, so that the third network device generates a first route whose destination address is a second IP address, where a next-hop IP address of the first route is the IP address of the first network device, and the second IP address belongs to the IP network segment. The first network device sends a second LSA packet to the third network device when determining that switching needs to be performed on a next hop of a route that is in the third network device, whose destination address belongs to the IP network segment, and whose next-hop IP address is the first IP address. In this way, one LSA packet can be sent to enable the third network device to switch, from the first network device to a second network device, the next hop of the route belonging to the IP network segment, thereby improving a speed of a route update.