ISIS protocol
1. Introduction: ISIS (Intermediate System to Intermediate System from), based on the link state protocol spf algorithm, but also an interior gateway protocol. ISO OSI protocol stack is defined by no connection to the network part of the service CLNS for dynamic routing of data packets.
Integrated ISIS supports CLNP network or IP network, or run double CLNP and IP network.
ISIS current specification is called the intermediate network node to the system, other protocols such as OSPF router is called the node.
Integrated ISIS: Internet Engineering Task Force (IETF) defines the "use OSI ISIS implemented in TCP / IP and OSI routing dual environment" that is "integrated ISIS" or "double ISIS" in RFC1195.
2. Features: security, stability. Do not rely on ip. (Operators are almost level 2)
3.ISIS basic principles:
3.1 the ISIS address structure:
the NSAP: OSI protocol address is used to define the resources corresponding to the OSI network layer protocol CLNP address, IP address similar concept.
NET: is a special kind of NSAP (SEL = 00), ISIS configure on the router, you only need to consider the NET.
Most of ISIS are using the NET
SAP:
* Composition of the IDP and DSP, the DSP and IDP length is variable, the NSAP total length of up to 20 characters, a minimum of 8 bytes.
* IDP network number corresponding to the IP address specified by ISO ,, it, and is composed of two parts AFI and IDI. AFI address assignment mechanism and the address format, IDI for identification field.
* DSP corresponds to the IP address of the subnet number and host address, which is a HIGH ORDER DSP, system ID and SEL three parts. HIGH order DSP is used to divide areas, System ID identifies a host, SEL to indicate the type of service.
* Area Address (Area ID) and the IDP HIGH order DSP DSP in composition, not only can identify a routing domain, it is possible to identify regions in the routing domain. Thus, they are together referred area address.
* System ID is used to uniquely identify the host router area. Realized in the device.
* In the ISIS protocol, a device may be configured to a plurality of the NET, but Area ID of each address can be different, but have the same system ID.
* AFI = 49 is the address of the OSI protocol private address analogy 10.0.0 TCP / IP or the like in
Precautions:
* An intermediate systems (routers) has at least one NET (there may be up to 254)
* Same intermediate AREA must have the same system ID AREA
* Each intermediate system must have a unique System ID in an Area of
* Two level-2 intermediate systems in a domain can not have the same System ID
* NSAP at least 8 bytes, up to 20 bytes
* For ip applications, a definition of the AFI byte (the address field identifies the binary syntax DSP), a minimum of 2 bytes define the actual area information, and 6 bytes define the system ID of the SEL 1 byte, so NSAP address happened 10 bytes.