IS-IS Basic Concepts

IS-IS Basic Concepts
Technorati label: CCIS, ISP, IS-IS, IS first. ISIS --- Intermediate System-Intermediate system ---- Intermediate system terminology: IS: Intermediate System Intermediate system (Router) DIS: Designated Intermediate system specify Intermediate system (Designated Router) ES: end system (Host) SysID: System ID (Router ID) PDU: Packet data unit packet data unit (IP Packet) LSP: link State Protocol Data unit Link State Data unit (ospf lsa with route information) LSPDB: LSP database (similar to OSPF LS DB) NET: Network Entity Title Network Entity tag. (For special NSAP, the last byte is 0, router ID + Area ). the last byte is always 0. there is no application in the IP address. NSAP: Network Service Access Point (CLNP address + Service port Number 0) IIH: Intermediate system to Intermediate system Hello PDU (equivalent to OSPF hello packet) PSNP: Partial sequence Number protocol data unit. similar to ospf ack. part of the serial number protocol data unit. CSNP: Complete sequence numbers protocol data unit. similar to the DBD packet of OSPF. all serial number protocol data units. features of The Link Status Protocol: Each router maintains its own connection chain Router Information and status, indicating the vro you are connected to and the cost overhead of A vro or network. At first, you only know your local topology information. A reliable Diffusion algorithm is used to collect topology information from other routers to form a network-wide topology, the SPF algorithm is used to calculate the route table.

IS-IS a part of the connectionless Network service (CLNS) defined by ISO in the OSI protocol stack. It IS used to run dynamic route data packets. -- CLNS consists of the following three protocols: 1. CLNP: similar to the IP protocol in TCP/IP. the IP protocol is a TCP/IP transport layer service, and CLNP is an OSI transport layer service. 2, IS-IS: the routing protocol of the intermediate system, similar to the OSPF.IS-IS in the ip is the protocol between the system and the system. 3, ES-IS: the protocol between the host system and the intermediate system, like ARP in the IP, ICMP (RD) and so on. ES-IS is the protocol between the host and the system. similar to the IGMP protocol. information is automatically exchanged between the ISO Terminal System and routers of the same network segment or link to facilitate discovery of adjacent nodes. the router sends the is message hello (ISH), and the host sends Hello (ESH ). the Hello message sent from the direct connection node contains the network layer address and data link address of the communication node. contained location Address Allocation, Gateway selection, and other functions. Equivalent to ICMP, ARP, and DHCP in an IP address. here we will focus on the address addressing method of ISIS. NSAP: Network Service Access Point (Network layer Address + Service port number) NET: Network Entity title (Special NSAP, the last byte is 0) ■ simplified NSAP format ■ Area Address by AFI, IDI also consists of a part of the DSP, which is used to indicate the organizational structure. ■ The system ID must be unique in the entire region and on the master (level2) to uniquely identify the host or router. ■ The System ID is 6 bytes. ■ NSEL (NSAP-Selector) NSAP indicates the selected service, which is equivalent to the port number in the TCP/IP address. For the NET address, it is 00. ■ an intermediate system must have at least one NET (up to 254) and the system ID must be the same. by default, the cisco system has three NET addresses at most. To modify the number, run the following command: router (config-router) # max-area-addresses xx (0-254) ■ The Intermediate system of the same Area must have a unique system ID. ■ two Level-2 intermediate systems in a domain cannot have the same system ID. ■ on a Cisco router, NSAP consists of at least 8 bytes and at most 20 bytes. Why 8 bytes: 1 bytes area + 6 bytes system ID + 1 byte N-selector. ■ for IP applications, one byte defines AFI (indicating the address of the binary DSP syntax), at least two bytes defines the actual region information, and six bytes defines the system ID and 1 byte NSEL. therefore, the NSAP address must be at least 10 bytes. for the definition of the NSAP address of ISIS, the cisco Document is as follows: how to set a system ID? On the "IS" page that supports IP addresses, set system ID (recommended for ease of management). Use the loopback interface IP Address: 192.168.3.25. The Area of the router, Area: 49.0001, to establish a systeming between the IP address and the systemID: