IS-IS protocol principle and configuration

The source of the routing entry

Direct Routing

Indirect routing

Static Routing

Dynamic Routing

IGP Interior Gateway Protocol

​ Distance vector: RIP

​ Link Status: OSPF ISIS

EGP Exterior Gateway Protocol: BGP

ISIS Intermediate System to Intermediate System

ISIS protocol is a dynamic routing protocol developed by the ISO national standardization organization for the CLNP protocol in the OSI model. Due to the strong scalability of ISIS, it supports both CLNP and IP protocols.So what is now called ISIS is called Integrated ISIS

ospf----TCP/IP----IP

ISIS----OSI/TCP/IP----IP/CLNP

Scenario application

OSPF - Campus Network - Application Protocol

ISIS—Backbone—Service-Based Protocol

Address Structure

NSAP address: main network + subnet + host + SEL (protocol type)

NET identifier: is a special NSAP address, when SEL=00, the NSAP address becomes the NET identifier

How Dynamic Routing Works

1. Establish neighbor relationship

2. Synchronize the database

3. Calculate the routing table

Router classification

level-1 router ----- quite a special area of ​​OSPF

level-2 router-----equivalent to the backbone area of ​​OSPF

level-1-2 router ---- equivalent to OSPF ABR area border router

level-1 neighbor relationship

Same area: level-1 router and level-1 router or level-1-2 router

level-2 neighbor relationship

Same area: level-2 router and level-2 router or level-1-2 router

Different regions: establishing level-2 relationships

Neighbor HELLO message

Establishing neighbor relationships

Network Type

1. Point-to-point network: P2P IIH (mac: 0180-C200-0014)

2. Broadcast network L1 lan IIH (mac: 0180-C200-0015)

State Mechanism

1, down

2, init

3, up

DIS and the analogy between DIS and DR

Barrier of link state information

Establishing neighbor relationships—IIH

Information

​ —SNP (Sequence Number Message)

​ —CSNP (Complete Sequence Number Message) ----equivalent to DD in OSPF

​ —PSNP (Partial Sequence Number Packet) ----equivalent to LSR/LSACK in OSPF

Inter-area routing

1. The layer where the L2 neighbor relationship is located - with detailed routing

2. The layer where the L1 neighbor relationship is located - with a default route pointing to the L1/2 router for external access

3. The L1/2 router sets the ATT field to 1, and the L1 router receives the information with the position 1, and generates a default route pointing to the L1/2 router

The difference between IS-IS and OSPF

IS-IS configuration

1. Configure basic IP information

2. Configure ISIS

​ - start ISIS

​ — configure the NET identifier

​ ——Configure the router type

3. The interface participating in the ISIS calculation starts the ISIS process

4. Verify

Configuring ISIS

isis 100network-enytity 49.0012.0000.0001.00//Configure the net identityis-level level-1//Configure the router type

The interface participating in the ISIS calculation starts the ISIS process

interface g0/0/0isis enable 100interface LoopBack 0isis enable 100

Test View

dis isis peer//View neighbor relationship informationdis isis route // View ISIS routedis ip routing-tableprotocol isis

Route leak

When there are more than two L1/2 routers (ABRs) in the non-backbone area, since the area inside the area accesses the external area through the default route pointing to the L1/2 router, the optimal route calculated internally is in the entire network.The path selection may not be optimal, and there may be sub-optimal paths.Therefore, through route leakage, the detailed route of the backbone area is leaked to the sub-area, and the detailed route of the whole network is obtained.With accurate calculation, sub-routing problems are avoided.- Leaked on ABR

isis 100import-route isis level-2 into level-1