The basic concept of Is-is

Technorati Tags: ccis,isp,is-is,isis, operator

First ISIS is a link-state protocol.

ISIS---Intermediate system-intermediate system Intermediate system----intermediate systems

Related terms:

is : Intermediate System Intermediate systems (Router)

DIS: Designated intermediate system designation Intermediate systems (designated Router)

ES: End System (Host)

Sysid: System ID (Router ID)

PDU: Packet Data Unit packet (IP Packet)

LSP: Link State Protocol Data Unit link status Data units (LSA of OSPF, lead-through information)

lspdb: LSP DB LSP Database (similar to OSPF LSDB)

NET: Network entity Title. (Special Nsap, the last byte is 0,router id+area). The last byte is always 0. There is no application in IP.

NSAP: Network Service Access Point (CLNP address + service port number 0)

IIH: Intermediate system to Intermediate system Hello PDU (equivalent to OSPF hello message)

PSNP: Partial Sequence number protocol data unit. An ACK similar to OSPF. Called Partial serial Number protocol data unit.

CSNP: Complete Sequence Numbers protocol data unit. A DBD message similar to OSPF. Call all serial number protocol data units.

Features of the link state protocol:

Each router maintains its own link information and status, indicating which routers it connects to, how much overhead it costs to a router or network, and initially knowing only a little bit of its own local topology information.

Through the reliable diffusion algorithm, each router collects topological information from other routers, and forms a topology map of the whole network consistent and complete topology, and relies on the SPF algorithm to calculate its own routing table.

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Basic features of ISIS protocol

--is-is is part of the CLNS (connectionless Network Service) in the OSI protocol stack, defined by ISO, for running dynamic routed packets.

--clns is comprised of the following three protocols:

1, CLNP: Similar to the IP protocol in TCP \ IP. The IP protocol serves the TCP/IP transport layer, and the CLNP serves the OSI transport layer.

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2, Is-is: The routing protocol of the intermediate system, similar to OSPF in IP.

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Is-is is the system-to-system protocol.

3, Es-is: The protocol between the host system and the intermediary system, like ARP in IP, ICMP (RD), etc.

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Es-is is the protocol between the host and the system. A bit similar to the IGMP protocol.

Automatic exchange of information between ISO terminal systems and routers on the same network segment or link facilitates discovery of adjacent nodes. The router sends the IS message Hello (ISH), and the host sends Hello (ESH). The Send hello message on the Direct Connect node contains the network layer address and the data link address of the communication node.

Includes address assignment, gateway selection and other functions. The equivalent of ICMP,ARP,DHCP in IP works together.

Here you'll learn about ISIS address addressing methods.

Nsap:network Service Access Point (Network Layer address + service port number)

Net:network Entity Title (Special Nsap, last byte is 0)

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Simplified NSAP format

The area Address is made up of Afi,idi and a part of the DSP, which is used to mark the organizational structure.

The system ID must remain unique across the entire region and backbone (LEVEL2) to uniquely identify the host or router.

The System ID is 6 bytes.

The Nsel (nsap-selector) NSAP flag, which indicates the selected service, is equivalent to the port number in the TCP/IP address, which is 00 for the net address.

An intermediate system is at least one net (up to 254) and the system ID is the same.

The Cisco system defaults to 3 net addresses up to, if necessary, with the following command:

Router (config-router) #max-area-addresses xx (0-254)

Intermediate systems in the same area must have a unique system ID.

The two Level-2 intermediate systems in a domain cannot have the same system ID.

The NSAP on a Cisco router is at least 8 bytes, up to a maximum of 20 bytes.

Why is 8 bytes:

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1 bytes area+ 6 bytes System ID + 1 byte n-selector.

For IP applications, the 1-byte definition of AFI (the address that identifies the binary DSP syntax), a minimum of 2 bytes to define the actual area information, and 6 bytes to define the system ID and 1 bytes of Nsel. Therefore, the NSAP address is at least 10 bytes.

For the NSAP address definition for ISIS, the Cisco documentation is as follows:

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How to set up a system ID?

How to set the system ID on an is that supports IP (recommended for easy administration)

Using the Loopback interface IP address: 192.168.3.25

Router Area area:49.0001

Establish the corresponding relationship of IP address to SystemID:

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The basic concept of Is-is