2022-06-17 advanced network engineering (IX) is-is- principle, NSAP, net, area division, network type, and overhead value

IS-IS

IS-IS（Intermediate System to Intermediate System, Intermediate system to intermediate system ） yes ISO （International Organization for Standardization, International Organization for Standardization ） For its CLNP（ConnectionLessNetwork Protocol, No connection network protocol ） A kind of design Dynamic routing protocol .

With TCP/IP Popularity of protocols , In order to provide for IP Routing support ,IETF stay RFC1195 Chinese vs IS-IS Expanded and modified , So that it can be applied to TCP/IP and OSI（Open System Interconnect, Open system interconnection ） Environment , We will expand the IS-IS be called Integrate IS-IS.

IS-IS yes ISO Defined OSI Protocol stack Of CLNS（ConnectionLess Network Service, No connection network service ） Part of .

IS-IS It's a kind of Link state routing protocol ,IS-IS And OSPF in many ways Very similar , For example, running IS-IS The directly connected devices of the protocol send messages through the Hello Messages find each other , Then establish adjacency relationship , And exchange link status information .

CLNS It consists of the following three parts ：

CLNP： Be similar to TCP/IP Medium IP agreement .

IS-IS： Be similar to TCP/IP Medium OSPF.

ES-IS： Be similar to TCP/IP Medium ARP,ICMP etc. .

ES：End System, Terminal system , Be similar to IP Hosts in a network environment .

ES-IS：End System to Intermediate System, Terminal system to intermediate system

Relevant command ：

establish isis process

[R1]isis 1

And OSPF contrast

Integrate IS-IS characteristic ： Support CLNP The Internet 、IP The Internet , Data link layer encapsulation is adopted

OSPF characteristic ： Only support IP The Internet , use IP Message encapsulation

NSAP

NSAP（Network Service Access Point, Network service access point ） yes OSI Protocol stack be used for Locate the address of the resource , It is mainly used for Provide interface between network layer and upper layer application .NSAP Include IDP And DSP.

IDP（Initial Domian Part） amount to IP The primary network number in the address . It is from ISO Regulations , And by the AFI（Authority and Format Identifier） And IDI（Initial Domain Identifier） Two parts .AFI Indicates the address allocation organization and address format ,IDI Used to identify the domain .

DSP（Domian Specific Part） amount to IP Subnet number and host address in address . It consists of High Order DSP、System ID and SEL Three parts .High Order DSP Used to divide areas ,System ID Used to distinguish hosts , It is equivalent to OSPF Medium router-id,SEL（NSAP Selector） Used to indicate the type of service , Usually it is 00, On behalf of IP agreement .

NET

NET（Network Entity Title, Network entity name ） yes OSI Of devices in the protocol stack Network layer information , The main Used for routing calculation , from Regional address （Area ID） and System ID form , It can be seen as special NSAP（SEL by 00 Of NSAP）.

NET The length of NSAP In the same , The longest is 20Byte, The shortest is 8Byte. stay IP Running in the network IS-IS when , Just configure

NET, according to NET The address device can get Area ID as well as System ID.

Area ID from IDP and DSP Medium High Order DSP form , It can identify the routing domain , It can also identify the region in the routing domain . therefore , Together they are called area addresses , amount to OSPF Area number in .

In general , A router only needs to configure one area address , And the area addresses of all nodes in the same area must be the same . In order to support smooth merging of regions 、 Segmentation and conversion , By default , One IS-IS Up to... Can be configured under the process 3 Area addresses .

System ID It is used to uniquely identify the host or router in the area . In the implementation of the device , Its length is fixed to 6Byte.

Area ID Variable length , by 1-13 byte

NET Address length example ：

Usually the length

49.0001.0000.0000.0001.00

Longest bytes

49.0000.0000.0000.0000.0000.0001.0000.0000.0001.00

Minimum bytes

49.0000.0000.0001.00

Relevant command ：

establish NET

[R1-isis-1]network-entity 49.0001.0000.0000.0001.00

Declare interface

[R1-GigabitEthernet0/0/0]isis enable 1 isis

Restart the process

<R1>reset isis all

Look at the neighborhood table

<R1>display isis peer

Set the name

[R1-isis-1]is-name R1

Zoning

IS-IS Backbone and non backbone regions are adopted in the autonomous system Level two Hierarchical structure of ：

Level-1 Router Deployed in Non backbone areas , It belongs to intra region routing .

Level-1 Can't communicate with the router Level-2 Routers establish adjacency ,Level-1 The router is only responsible for maintenance Level-1 Link state database LSDB, The LSDB Only the routing information of the region is included .

Level-2 Router 、Level-1-2 Router Deployed in Backbone area .

Level-2 The router maintains a Level-2 Of LSDB, The LSDB Including the whole IS-IS All routing information of the domain .

Level-1-2 Router and OSPF Medium ABR Very similar ,Level-1-2 The router maintains two LSDB,Level-1 Of LSDB For intra area routing ,Level-2 Of LSDB For inter area routing .

Every non backbone area goes through Level-1-2 The router is connected to the backbone area .

By default, the router level is Level-1-2.

level-1 Establish a neighbor relationship between routers ,Area ID It has to be consistent ;

level-2 Establish a neighbor relationship between routers ,Area ID It can be inconsistent .

therefore , In order to take care of level-1 Router , When only 1 platform Level-1-2 Router ,Area ID Must be with level-1 Router consistency , otherwise level-1 Router and level-2 The router cannot communicate .

Level-1-2 Establish a neighbor relationship between routers ,Area ID It can be inconsistent ; When consistent, press Level-1 Level announcement , When it's inconsistent , Will press Level-2 Level announcement .

Level-1-2 The router can modify the interface Level Grade , Determine the level and type of announcement

Relevant command

Modify level

[R1-isis-1]is-level level-1

Modify the interface level

[R1-GigabitEthernet0/0/0]isis circuit-level level-1

.

Network type

IS-IS The default network type of the interface will be automatically determined according to the data link layer encapsulation of the interface

 IS-IS Two types of networks are supported ：1. radio broadcast （Broadcast） 2. Point to point （P2P）

Relevant command

Modify the network type

[R1-GigabitEthernet0/0/0]isis circuit-type p2p 

Cost value

IS-IS Use Cost（ expenses ） As a routing metric ,Cost The smaller the value. , The better the path . default Cost by 10.

IS-IS There are two types of overhead ：1.narrow（ Narrow metric ）, The default type , Range 1-63   2.wide（ Width measurement ）, Range 1-16777214, expenses = Reference bandwidth / Interface bandwidth *10, The default value of reference bandwidth is 1000.

Relevant command

Modify the global cost

[R1-isis-1]circuit-cost 20

Modify interface overhead （ The highest priority ）

[R1-GigabitEthernet0/0/0]isis cost 20

Automatically calculate overhead （ The lowest priority ）

[R1-isis-1]auto-cost enable 

Narrow metric case The corresponding relationship under

Width measurement You need to modify the overhead type and reference bandwidth

[R1-isis-1]cost-style wide

[R1-isis-1]bandwidth-reference 10000