The Design And Application Of ISIS Protocol In China Unicom's IP Bearer Network

As the rapid development of Internet, network communication has become the main means of communication. Flexible IP routing protocols are essential to ensure the effective and reliable communications. In today's networks, link-state routing protocols such as OSPF and ISIS are dominant, which are the preferred IGP protocol for large networks. Integrated ISIS protocol can be used both CLNP environment and pure IP environment with good compatibility. In addition, ISIS works in the network layer, it is more secure than OSPF, which works over the IP. And ISIS uses TLV, by adding a new TLV to achieve easy and flexible extensions. Therefore, ISIS becomes mainstream IGP protocol.As the core of the network, routing protocol can be used to release and obtain the correct routing information, in addition, must be able to guarantee the reliability and stability of the routing, and find link status changes in time, and make the network fast convergence. Especially in large networks, the problem, such as unreliable routing, instable routing, or slow convergence, will have serious implications for the network. Graceful Restart is a redundant fault-tolerant technology, the routers supportting GR have the ability to ensure normal traffic forwarding, when restart the routing protocol. The restart of ISIS protocol will cause network interruption, incorrect routing calculations and packets loss. It is because the adjacent relationship were removed between routers, and the LSP message is deleted. This kind of problem can be solved by using ISIS GR, which allows the router send status notification to the neighbors, to maintain a forwarding table and ensure the stability of routing. To increase network availability and reduce the effects of the equipments failure, it must be able to detect communication failures between adjacent devices as soon as possible. Bidirectional Forwarding Detection can solve the inadequacy of existing detection mechanisms. It can provide the light load and short duration test between adjacent forwarding engines. It can provide test for all types of media and protocol layer by using a single mechanism. BFD can detect the link failures between ISIS neighbors quickly, and report to the ISIS protocol. Combined with the other IGP fast convergence technology, such as incremental shortest path first calculation, part routing calculation and smart timer, the ISIS network can achieve fast convergence.In this paper, I study the integrated ISIS protocol in detail from several aspects: packet format, area, adjacent relationship, building, and link-state update process. And adiscussed the implementation method for using ISIS GR to achieve a grace restart, using the fast convergence of ISIS to achieve the fast convergence of the network, and using BFD to achieve fast link failure detection, also verified its effectiveness base on the HuaWei router. In addition, discussed the possible reason and common solutions of the routing problems in the ISIS network construction.