zte is-is protocol

5/22/2018 ZTE IS-IS Protocol

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IS-IS Protocol Principle

V1.0


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Purpose

The purpose for studying the contents is to: Understand the basic concept of the ISIS.

Master the area division of the ISIS.

Master the routing calculation process of the ISIS.


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Basic Concept of the ISIS

Hierarchical Division of the ISIS

Neighbor Establishment of the ISIS

Database Maintenance of the ISIS

Routing Calculation of the ISIS

Comparison of the ISIS and the OSPF

Contents


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IS-IS Overview

IS-IS: dynamical routing protocol in the opensystem interconnect (OSI) (OSI 10589 or

RFC1195)

Integrated IS-IS can support both of ISO and

TCP/IP

IS-IS: the IGP protocol

IS-IS: similar to the link-state protocol OSPF of

routing protocol


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Same Points of the ISIS and the OSPF

Maintain the database of a link state and use the SPFalgorithm to calculate a shortest path tree;

Use the Hello packet to form and maintain the neighbor

relation;

Use the area concept or different level to form a two-levelhierarchical topology;

Have the capability to provide the address summarization

among areas;

Classless routing selection protocol; Select an specified router to describe the broadcast type

network;

Have the authentication capability.


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OSI and TCP/IPOSI TCP/IP

End System (ES) Host

IntermediateSystem (IS) Router

ES-IS

Communication protocol

from the host to the router

Proxy ARP

and others

IS-IS

Routing selection protocol

OSPF

Protocol Data Unit (PDU) packet

DLPDU

Data link PDU

Frame

NPDU

Protocol Data Unit in the

network layer

Packet and

group

OSI TCP/IP

CLNP

No connection network

protocol

IP protocol

NSAP

Address and identifier

IP address

Subnetwork Point of

Attachment (SNPA)

Subnet

LSP (IS-IS)

PDU of link status. It is

the packet.

LSA (OSPF)


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ISIS Address StructureNET

NET Address (Network entity title ) The address of the OSI network. It is called the NET address. It is

used to describe the area ID and the system ID of the device.

Area: the area number. The length is variable from 1 to 13 bytes.By default, one router can have three area numbers.

ID: the system ID. It is similar to the Router ID in the OSPF. Thelength is variable. Commonly, it is 6 bytes. It is identified by usingthe interface MAC. It is unique in the area.

Sel: selection character. It is similar to the IP protocol number. It isset to 0x00. It means a NET address.


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Example of the NET Addresses

39.0f01.0002.4444.4444.4444.00

39.0f01.0002.3333.3333.3333.00

39.0f01.0003.6666.6666.6666.00

39.0f01.0004.7777.7777.7777.00

39.0f01.0001.2222.2222.2222.00

39.0f01.0001.1111.1111.1111.00


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Database Maintenance of the ISIS Routing Calculation of the ISIS


Contents


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Area Division of the ISIS

IS-IS is composed of L2 backbone area and L1non backbone area.

The following routers run the IS-IS router:

L1 router (routing inside the area)

L2 router (routing among areas)

L1/L2 router (similar to the ABR router of the OSPF)


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Area Comparison of the ISIS and the OSPF

Area

0

A

B

C D

E

F

Area1

Area

2

ABR

ABR

The area division of the OSPF is

done on the router.

A

B

C D

E

F

L1

Area

2

L1/L2

L1/L2

L1

L2L2

The area division of the ISIS is done on the link.


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Features of the ISIS

The area division of the IS-IS is done on the link.The whole router is in one area.

To prevent routing loop among areas, the

communication among areas must pass through

L2 area. Therefore, L2 router must be directlyconnected.

The L1/L2 router only notifies the routing of L1

type to L1 router. The L1 area is equivalent to thetotally-stub area of the OSPF protocol.


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L1 Router and L2 Router

Level1 router: It can only be neighbor with the routers in the area.

It has the level1 LSDB which contains all routing

information in the area.

It uses the nearest L1/L2 router to leave the area. It may have the sub optimization routing.

Level2 router:

It can be neighbor with routers in other areas.

It has the level2 LSDB which contains all routing

information in other areas.


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L1/L2 Router

L1/L2 router:It can have neighbors of other areas.

It has two LSDBs:

Level1 LSDB about the internal routing information in the area

Level2 LSDB about routing information among areas

If one router has the adjacency relation with other

routers, it may pass through other Level1 router in

the area: it is the potential exit of the area itself.


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Network Hierarchical Structure of IS-IS


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Contents


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Working Progress of the ISIS

Establish the adjacency relation; Send the LSP and synchronize the database

information of the link status;

Use the SPF algorithm to calculate the best routes.


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Neighbor Establishment Process of the ISIS

Send the Hello packets (IIH PDU) in period (10s)to find the neighbors;

Match the parameters to establish the adjacency

relation.

Init

Learn the neighbors. But the adjacency

relation is not formed;

UP Establish the adjacency relation.


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Hello PDUIIH

IIH interconnects with others to form adjacency among

ISIS routers.

Classification of the IIH:

P2P IIH (used for point to point network)LAN IIH (used for broadcast type network)

-- LAN Level1 IIH (0180.C200.0014)

-- LAN Level2 IIH (0180.C200.0015)

IIH fulfills the MTU. Only when the MTUs in the two ends

are consistent, then the adjacency can be formed.


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Hello PDUIIH


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Three Handshakes for Establishing Neighbor

Enter the init status when receiving the hello packet of theneighbor;

Enter the UP status when finding the MAC of itself in the

TLV of neighbor hello packet.


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The election of the Designated ISDIS

Reduce the neighbor information carried in the LSP sent inthe broadcast type network and simplify the networkstructure.

In the broadcast type network, We should elect designatedrouter for L1 and L2 areas respectively .

All neighbors need to establish the adjacency relation.

DIS assigns LAN IDs of the network. It is composed of thesystem ID of the DIS

Election principle-- The interface is specified with a L1 type priority and a L2 type

priority. The range is 0127. The larger the number is, the higher the

priority is;-- When the priorities are the same, see the MAC addresses of

the interfaces. The larger the number is, the higher the priority is;

-- The DIS is not stable and it can be preempted .


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DIS on the Broadcast Link


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Basic Concept of the ISIS Hierarchical Division of the ISIS




Contents


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Maintenance of the Database

LSP: link state PDU

Exchange the routes information, establish and maintainthe LSDB .

CSNP: Complete Sequence Number PDU

In the point to point and broadcast link, CSNP is used to

check the consistency of the LSDB

PSNP: Partial sequence number PDU

The two main functions :

In the point to point link, it is used to confirm the received

LSP;In the point to point and broadcast link, it is used to requestthe newest version or lost LSP.


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LSPLink State PDU

Two types of LSPLSP generated by non pseudo node

LSP of the LAN represented by pseudo node

(generated by DIS)

Level 1 router generates Level 1 LSP

Level 2 router generates Level 2 LSP

Level 1-2 router generates Level 1 LSP and Level

2 LSP


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Generation of Non Pseudo Node LSP

In the following conditions, each IS routergenerates and disperses the non pseudo node

LSP:

New neighbor joining or leaving

New IP prefix adding or removing

Changing of the metric of link

Refreshing timer overflow


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Generation of Pseudo Node LSP

Pseudo LSP is generated by DISEach layer generates a LSP

Each LAN generates a LSP

Pseudo node LSP can reduce the adjacency andflooding

In the following conditions, DIS generates and

floods new pseudo nodes LSPs :

New neighbor joining or leaving

Refreshing timer overflow


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Generation of Pseudo Node

Broadcast link is represented by a virtual node, which is calledpseudo node (PSN).

Pseudo node

Only DIS can generate the PSN

The DIS election is preemptive. It is determined by the interface

priority. If the priorities are consistent, it is determined by the MACaddress. The larger the number is, the higher the priority is.

There is only DIS and no backup DIS. DIS is helpful for the routersin the broadcast link to synchronize LSDB.

DIS

PSN

DIS


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LSP Database (No PSN)


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LSP Database (Carried with PSN)


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LSP Packet


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CSNP Packet


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PSNP Packet


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Contents


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Calculation of the RouteMetric

Default: default metric (necessary) Delay: pass-through delay of a subnet (optional)

Expense: cost of a subnet (optional)

Error: show the remaining error problems of the subnet. It

is similar to reliability metric of IGRP/EIGRP (optional).

Each metric is expressed by 063. each kind of metric is

calculated by the separated independent routing.

Therefore, if one system supports the four metrics. SPFcan make L1 and L2 to calculate four times. The router

SPF to the destination can be calculated repetitiously.


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Calculation of RouteBest Router Selection

If there are multiple routes to a destination : The path of L1 is prior to the path of L2

If the path supports the optional metric, then it is prior to

the default metric

The route with lowest metric is prior than others in eachlevel

If there are multiple paths with the same cost in the

routing table, you can use the load balancing. There are

six at most(depend on router).


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Contents


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Same Points of the ISIS and the OSPF(1)

They are both the link state protocols and use the SPF

algorithm to calculate the routes.

They both have the fast convergence and loop free

function. They are capable for large networks.

They both use the hello protocol to maintain the neighborrelation.

They both use the hierarchical routing concept. They both

have the backbone areas, which can provide the agile and

actual design plan for the network planning.


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Same Points of the ISIS and the OSPF(2)

To control the scale and complexity of LSDB , DR/DIS is

elected on the broadcast network.

They both support the authentication.

They both use the interface configurable cost for route

metric .

They both have the capability to provide the address

summarization among areas.

They both support the classless routing selection protocol.


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Distinctions of the ISIS and the OSPF(1)ISIS OSPF

Protocol model OSI model

Design for CLNS. It is added with the

support of the IP.

TCP/IP model

It is dedicated for the IP network.

Packet

encapsulation

Run in the link layer. The packet is

directly encapsulated in the packet of

the link status. It supports multiple

protocols, such as CLNS and IP.

Packet is encapsulated in the IP. It only

supports the IP protocol.

Network type Broadcast type and point to point Broadcast type, point to point, point to

multiple points, NBMA and virtual link

Area Backbone area is not a specified area. It

is composed of continuous Level 2

routers.

Area border is in the link among routers.

By default, the ISIS is the stub area. L2

cannot leak routing information to L1.

Backbone area is area 0

Area border is on the ABR router

By default, it is not the stub area.

DR/DIS Preemptive. No BDR.

In the broadcast network, the router and

all neighbors establish the adjacency

relation.

Non preemptive. Have BDR.

The router only establishes the

adjacency relation with DR and BDR

neighbors.

Adjacency

establishment

Establish the adjacency relation through

the hello packet. and establish

adjacency

Establish the neighbor relation through

the hello packet, and establish

adjacency after LSDB synchronization


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Distinctions of the ISIS and the OSPF(2)

ISIS OSPF

LSDB Use LSP. It is a packet .

The initial database synchronization is

done after the establishment of the

adjacency relation.

Use LSA. It is encapsulated in the IP

packet.

The initial database synchronization is

done before the establishment of the

adjacency relation.

SPF algorithm Run Level 1 SPF in the area to

calculate the routings.Run Level 2 SPF in the area to

calculate the routings.

Run SPF in the area to calculate the

routings.Run distance vector algorithm among

areas to calculate the routings.

Scalability ISIS can neglect the TLV type that it

does not support.

All OSPF routers in the network must

identify all used extension and LSA

options.

Applicable

range

It is commonly used in the large ISP. It is commonly used in the enterprise

network and large ISP.

Complexity Generate less LSP. Commonly, it uses

only one area.

Generate more LSAs. Commonly it is

configured with multiple areas.

Network scale It can support rather larger single area. For rather large network, it is commonly

divided to multiple areas.


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Summary

The chapter mainly introduces the

following contents:

Basic concept of the ISIS ISIS area division, database

maintenance and routing calculation

method



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Questions

1. How many kinds of the ISIS areas are there?What are the features of each kind?

2. What is the function of the hello packet of the ISIS?

3. Which kind of network generates the DIS? How is

it elected?


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zte is-is protocol

Documents

isis comparison

isis routing calculation

igp protocol

protocol principlev1

dynamical routing protocol

isis hierarchical division

area division

area concept