Currently, an Intermediate System to Intermediate System (ISIS) routing protocol adopted in the relevant art is a dynamic, link state-based Interior Gateway Protocol (IGP). After the ISIS routing protocol establishes a neighbour by an interactive negotiation of a HELLO message, each Intermediate System (IS) generates an LSP for describing link state information of the IS, and sends the corresponding LSP to a network. In addition, each IS stores LSPs sent by other ISs on a network topology so as to form a Link State Database (LSDB). The ISIS routing protocol uses the LSDB to compute an optimum route to a destination address via a Shortest Path First (SPF) algorithm.
In an integrated ISIS routing protocol, each LSP mainly includes a great amount of Internet Protocol (IP) reachability information, namely, IP prefix routing information. The IP reachability information mainly comes from two aspects as follows: 1. An IP prefix, configured on a three-layer routing interface self-configured by each IS, is notified in the corresponding LSP as the IP reachability information to represent that the IS may reach an routing network segment of the IP. 2. After each IS has been configured with route leaking or redistribution, an IP prefix in a three-layer routing table is notified in the corresponding LSP to represent that the IS may reach an IP routing network segment via a route in other layer of the IS or other routing protocols, wherein the three-layer routing table is self-generated by the ISIS routing protocol, or is generated by a routing protocol which is configured and correspondingly redistributed.
Each IS needs to notify link state information which may be divided into multiple types and is filled in the corresponding LSP in a Type Length Value (TLV) form. The corresponding LSP notified by each IS has a plurality of fragments, 256 at most. Each fragment corresponds to a number (0-255). Each fragment has a maximum length, defaulting to 1492 bytes. Under normal conditions, an LSP generated by an IS starts to be generated from an LSP of which a fragment is numbered as 0, when the LSP of which the fragment is numbered as 0 is filled to a maximum length, if there is still link state information which needs to be filled in the LSP to be notified, i.e., a fragment numbered as 1 is generated, and operations are carried out in the same manner until all pieces of link state information required to be notified are notified in the LSP. Consequently, the length of only the last LSP fragment among the LSP fragments may not reach the maximum length due to the completion of the link state information required to be notified, and the lengths of the other LSP fragments may reach the maximum length (1492).
Thus, in a large-scale network, a huge number of LSDBs are required to be notified. Particularly, a great amount of IP reachability information is required to be notified in the network usually, and therefore the IP reachability information occupies a majority of LSP fragments to be notified usually. When the occupied LSP length varies due to additions, deletions and changes (including: a metric change, a type change and an attribute change) of the IP reachability information required to be notified in the LSP, LSP regeneration of an LSP fragment and subsequent fragments is caused, thereby causing layout reorganisation of these LSPs. However, the layout reorganisation brings negative effects, namely, when a remote IS computes the IP reachability information notified by a current IS, certain pieces of IP reachability information have moved from a fragment to another fragment, and when these LSPs flood in the network, the remote IS firstly receives an LSP of which the IP reachability information is moved away, thereby deleting an IP route. When another LSP fragment is received after a period of time, the IP route may be recovered by re-notifying the IP reachability information in the LSP fragment, thereby causing route missing within this period of time, and traffic reaching the IP prefix is forced to be interrupted.
With the gradual enlargement of a network scale, the link state information required to be notified by each IS may be increased to a great extent accordingly, and therefore the LSPs required to be generated are increased day by day. However, oscillation, frequent increasing, deletions and changes (including: the metric change, the type change and the attribute change) of certain pieces of link state information (for example, IP reachability information) are caused due to certain reasons (for example, certain links are frequently up and down due to physical faults, routing of a redistribution protocol greatly oscillates, and the system-id of the ISIS protocol is repeatedly configured), and therefore many LSPs are continuously reorganised and updated. Thus, Central Processing Unit (CPU) resources of a local IS are greatly consumed. In addition, the efficiency of generating the LSPs by the ISs is reduced to a great extent accordingly. Before certain LSPs have time to respond to the previous change, a new turn of reorganisation and update starts, thereby increasing flooding loads of the LSPs on the network, and causing frequent oscillation of all IS routes in the network topology.