Comprehensive Analysis of IS-IS routing protocol (1)

We have briefly introduced the IS-IS routing protocol. As we all know, it is a standard between a standard route and a route. Now let's take a look at the specific content of this Protocol. The IS-IS protocol IS similar to the OSPF protocol. It IS both a link-State Routing Protocol. In fact, it appears earlier than the OSPF prototype, ospf is used in the route selection for Internet and TCP/IP network IP communication. IS-IS can be used in IP communication, it can also be used in OSI communication and can provide dynamic routing for Information Transmission groups between two routers in the same domain ｡

The so-called integrated IS-IS introduction the intra-domain routing information exchange protocol between the Intermediate System and the Intermediate System IS-IS (Intermediate System-to-Intermediate System intra-domain routing information exchange protocol) it was originally a dynamic routing Protocol designed by ISO for its connectionless Network Protocol CLNP (Connection-Less Network Protocol, to provide IP Routing Support, IETF expands and modifies the IS-IS in RFC1195 so that it can be applied to both TCP/IP and OSI environments, IS called Integrated IS-IS (Integrated IS-IS or Dual IS-IS )｡

The IS-IS routing protocol IS a link status protocol. It uses the Shortest Path First (Shortest Path First) algorithm, there are many similarities with the OSPF Protocol. The IS-IS routing Protocol belongs to the Internal Gateway Protocol IGP (Interior Gateway Protocol), used inside the autonomous system ｡

IS-IS Concept

(1) IS-IS routing protocol terminology

IS (Intermediate System, Intermediate System). equivalent to a router in a TCP/IP, it IS the basic unit for generating routing information in the IS-IS protocol and transmitting routing information. It has the same meaning as the router in the following article ｡

ES (End System). It IS equivalent to a host System in TCP/IP. ES does not participate in the IS-IS routing protocol, ISO has a dedicated ES-IS protocol to define the communication between the terminal system and the intermediate system ｡

RD (Routing Domain, Routing Domain). In a Routing Domain, a group of IS exchange Routing information through the same Routing protocol ｡

Area. The unit of the route field ｡

LSDB (Link State DataBase, Link State DataBase). All network connection States constitute a Link State DataBase, and each IS has at least one LSDB. IS uses the SPF algorithm, use LSDB to generate your own route ｡

LSPDU (Link State Protocol Data Unit). In IS-IS, each IS generates an LSP, this LSP contains all the link status information of this IS. Each IS collects all LSPs in the region to generate their own LSDB ｡

Network Protocol Data Unit (NPDU) IS a Network layer Protocol packet in ISO, which IS equivalent to an IP packet in TCP/IP. DIS (Designated IS) that is, the specified intermediate system of the broadcast network ｡

Network Service Access Point (NSAP) is the Network layer address in ISO. It is used to identify an abstract Network layer Access Service Point and describe the Network address structure of the ISO model ｡

IS-IS Route Protocol applicable link type

IS-IS can run on Point-to-Point Links, such as PPP and HDLC, or Broadcast Links, such as Ethernet and Token-Ring, for NBMA (Non-Broadcast Multi-Access) networks, such as ATM, You need to configure sub-interfaces for them, configure the sub-interface type as P2P or broadcast network. IS-IS cannot run on a Point to Multi Point Links ｡