OSPF protocol based on CCNP theory (II)

OSPF Open Shortest Path Priority Protocol)

Iii. Understanding of OSPF LSA

1. Type of LSA)

Class 1: Router LSA, Router LSA

Type 2: Network LSA and Network LSA

Class 3: Summary LSA, network Summary LSA

Class 4: ASBR Summary LSA Class 3 and Class 4 are collectively referred to as Summary LSA)

Class 5: External LSA, External LSA

Class 6: multicast OSPF LSA

Class 7: LSA defined for NSSA

Class 8: BGP external attribute LSA

9, 10, 11 categories: Opaque LSAs, non-transparent LSA

 

2. Explanation of common LSA

Type1: Router LSA

---- Each vro will generate

---- Transmitted only in this region, not across the ABR

---- Describes all Link Interface Information directly connected to the vro

 

Type2: Network LSA

Only multi-channel access to the network MA) will generate two types of LSA. Ethernet connection

---- Sent by DR

---- Transmitted only in this region, not across the ABR

---- Describes the routers and subnet masks in the MA network. Link Status IDlink-id) is the IP address of the DR to be advertised.

 

Type3: Summary LSA

---- Produced by ABR

---- The whole Autonomous System of pan-flood advertises Inter-Domain Routing

---- Advertise all route information of the domain, including the network number and mask

 

Type4: ASBR Summary LSA

---- Produced by ABR

---- Transmitted in other regions outside the region, so that vrouters in other regions can know the location of the ASBR.

---- Advertise the route to the ASBR, the rid of the asbr. The link status ID is the RID of ASBR. In the direct connection region of ASBR, four types of LSA are not generated, because ASBR generates one type of LSA, which indicates that it is an ASBR.

 

Type5: External LSA

---- Generated by ASBR, not in any region

---- General flood, the entire Autonomous System

---- Advertise external routes. The link status ID is the network ID of the external network.

 

Type7: NSSA

---- Generated by NSSA ASBR

---- Transmitted in this NSSA Region

---- Advertise external routes. Class 7 LSA only appears in NSSA

 

3. ospf lsdb and route table

View LSDB information: show ip ospf database

Link ID: identifies each LSA and identifies the LSA sent by different routers.

ADV Router: advertise the Router of LSA

Age: the longest-lived counter, which can be 3600 seconds at most.

Seq #: Serial number of the LSA. The initial value is 0x8000001. 1 is added when it is updated.

Checksum: the checksum of the LSA to ensure that the LSA is reliably received.

Link Count: the total number of links directly connected to the Router LSA only.

 

OSPF route type:

O: intra-region routes: Class 1 and Class 2 LSA)

O ia: Inter-region routing (Class 3 and Class 4 LSA)

O E1: five types of LSA for external routes, and the link overhead is external + internal)

O E2: five types of LSA for external routes, without considering the internal overhead)

 

Routing principle:

O> o ia> O E1> O E2

From non-backbone areas ---> non-backbone areas take precedence over backbone Areas

 

4. Understanding OSPF network types

There are three types of physical connections:

① -- Point to point)

② Broadcast)

③ Non-broadcast Multi-Channel Access Nonbroadcast, NBMA)

 

In the NBMA network, OSPF has five operating modes.

The following are the features of the five modes:

① Non-broadcast NBMA, RFC International Standard)

One IP subnet;

You must manually specify the neighbor <config-router> neighbor x. x

Select DR/BDR to ensure that the Hub side is DR. You need to manually add MAP ing;

The Hello time is 30 s;

 

② Point-to-multipiont point-multi point, RFC International Standard)

One subnet;

Automatically forms a neighbor relationship and multicast Hello groups;

Do not elect DR/BDR;

The Hello time is 30 s;

A 32-bit host route is generated;

No need to manually add MAP ing

 

③ Broadcast, Cisco Standard)

Automatically Forming a neighbor relationship;

Election of DR/BDR;

The Hello time is 10 s;

MAP ing needs to be manually added

 

④ Point-to-multipoint non-broadcast point -- Multi-point non-broadcast, Cisco Standard)

Manual neighbors;

No DR/BDR;

The Hello time is 30 s;

No need to manually add MAP ing

 

⑤ Point-to-point, Cisco Standard)

Automatically Forming a neighbor relationship;

No DR/BDR;

The Hello time is 10 s;

Each interface belongs to a different IP subnet;

No need to manually add MAP

 

Default OSPF mode:

The default mode is point-to-point on the point-to-point Frame Relay subinterface;

On the Frame Relay multipoint subinterface, the default mode is Non-broadcast;

The default mode is Non-broadcast.

 

When the network types at both ends are inconsistent, modify the Hello time and Dead time:

Point-to-point and point-to-multipoint can establish a neighbor, and the route is normal.

Both NBMA and Broadcast can create neighbors, and the routes are normal.

 

Modify the network type: <if> ip ospf network [...]

========================================================== ==============================

This article from the "building to listen to wind and rain" blog, please be sure to keep this source http://koulitsu.blog.51cto.com/7355117/1269491