[hcip] OSPF external route introduction

Catalog

5  class LSA

Different routers go to external routes

4  class LSA

External routing principles

FA  Address

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5  class LSA

ASBR： Devices that introduce external routes

When the router becomes ASBR  after , Will be generated in 1  class LSA  Center position ASBR  position , Identify yourself as ASBR, And convert the externally introduced route into  5  class LSA「External LSA」

Different routers go to external routes

and ASBR  Routers in the same area ：

Cost  Calculation ： Oneself to ASBR  Of Cost + ASBR  To an external route Cost

Next jump ： Oneself to ASBR  The next hop of the shortest path

and ASBR  Routers in different areas ：

Cost  Calculation ： Oneself to ABR  Of Cost + ABR  To ASBR  Of Cost + ASBR  To an external route Cost

Next jump ： Oneself to ABR  The next hop of the shortest path

4  class LSA

Sum-Asbr

effect ： Used to identify ASBR  The location of , notice ABR  arrive ASBR  Of Cost

How to produce ： from ABR  produce , When 4  class LSA  Transfer to other areas ,Adv rtr  and Cost  Will change

External routing Route selection principle

External routing types are divided into Type 1  and Type 2

Type 1： Accumulate internal Cost

Type 2： Do not accumulate internal Cost

（1）Type 1  be better than  Type 2

（2） A fellow  Type 1  Time comparison Cost,Cost  The same load

（3） A fellow Type 2  When compared with when introduced Cost, Then compare to arrive at ASBR  Of Cost,Cost  The same load

When the administrator wants the router to calculate the best path by itself Type 1; When the administrator wants to control the path by himself, use Type 2

1  class > 2  class  > 3  class  > Type 1 > Type 2

FA  Address

FA  Address 「Forwarding Address」

Path optimization for external routing

Generating conditions ：

（1）ASBR  The outgoing interface to the external route is added to OSPF  process

（2）ASBR  The outgoing interface for external routing is not a silent interface

（3）ASBR  The outgoing interface to the external route is not P2P  or P2MP

FA  The value of ：ASBR  The next hop address to the external route

How to realize path optimization ：

OSPF  The router will FA  Address as an exit to the external route ;Cost =  Self going FA  Of Cost +  Carried by external routes Cost; Next jump ： The router goes to FA  Next jump of address

import-route static type「 External routing type 」： Introducing static routing 
silent-interface「 Interface 」： Set this interface as a silent interface