LSA Type Explanation - lsa-5 (type 5 LSA - autonomous system external LSA) and lsa-4 (type 4 LSA - ASBR summary LSA) explanation

Catalog

One 、LSA-5

（1）—— brief introduction ：

（2）—— Header information :

（3） Data section :

（4） see ： 

Two 、LSA-4

（1）—— brief introduction ：

  (2)—— Header information ：

（3）—— Link data part ：

（4)—— How to view ：

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One 、LSA-5

（1）—— brief introduction ：

• Outside the autonomous system LSA（Autonomous System External LSA）： Or external LSA（External LSA）, It starts from ASBR Router Of , Used to announce arrival OSPF Destinations outside the autonomous system or OSPF Outside the autonomous system Default route Of LSA. Outside the autonomous system LSA It is the only one in the link state database that is not associated with a specific region LSA notice . external LSA Announcements will be made throughout the autonomous system flooding Spread . Use command show ip ospf database external You can see AS external LSA Information about .
• produce :ASBR Produced ( The router executes the redistribution command , Send the external route into OSPF Li Lai , This router is ASBR Router )
• Flood boundary : except stub Area , Completely stub Area ,NSSA Area , Completely NSSA It can be reached outside the area
• effect : In link state ID Inside, it advertises the external routes that are fully sent
• Be careful : stay OSPF Inside , Fully sending static routes can only fully invent fine static routes , The default route cannot be redistributed

（2）—— Header information :

• LS age : Aging time ,1800--3600 second , among 1800 It's cyclical LSA Refresh time ,3600 yes LSA Maximum aging time Options: optional
• LS Type : AS External Link
• Link State ID : Redistribute incoming external routes
• Advertising Router : This LSA Who made it , Just take this router RID Written here
• LS Seq Number : LSA The serial number of , Use this serial number to determine whose LSA Is the latest ,LSA Every update , Serial number +1
• Checksum : Parity sum , Used to verify the integrity of data transmission
• Length : It contains the total length of header information and data part
• Number of Links : I announced several OSPF link

（3） Data section :

• ---- Describe the mask that adequately sends in external routes
• ----cost value , The external route sent in fully defaults cost The value is 20
• ---- Describe the full incoming external routing cost Value type :OE2 and OE1, The default is OE2,OE2 Don't add up OSPF Within the domain cost value ;0E1 Cumulative OSPF Within the domain cost value
• ---- Forwarding address , The default forwarding address is 0.0.0.0: On behalf of going to this external route, send the data packet to ASBR Router

（4） see ： 

show ip ospf database external

Two 、LSA-4

（1）—— brief introduction ：

• ASBR Summary LSA（ASBR Summary LSA）： Also by ABR Router originated .ASBR Summary LSA Except that the destination announced is one ASBR Router instead of a network , Other and network Summary LSA It's all the same . Use command show ip ospf database asbr-summary You can see ASBR Summary LSA Information about . Pay attention here , One of the destinations is The host address , And the mask is 0; adopt ASBR Summary LSA The destination of the announcement will always be a host address , Because it is a route to a router .
• produce :ABR Produced
• Flood boundary : and LSA-5 equally
• effect : notice ASBR Who is routing , notice ASBR The router RID
• LSA-4 characteristic : Every time I pass by ABR Routers will respond to this LSA-4 Regenerate ,
• The main role ： Compute the ABR Router to ASBR Of cost value ; That is to say LSA-4 Every time I pass by ABR Will be able to Advertising Router and cost Value to be filled again

  (2)—— Header information ：

• LS age: Aging time ,1800--3600 second , among 1800 It's cyclical LSA Refresh time ,3600 yes LSA Maximum aging time Options: optional
• LS Type: Summary Links
• Link State ID: ASBR The router RID
• Advertising Router: This LSA Who made it , Just take this router RID Written here
• LS Seq Number: LSA The serial number of , Use this serial number to determine whose LSA Is the latest ,LSA Every update , Serial number +1
• Checksum; Parity sum , Used to verify the integrity of data transmission
• Length: It contains the total length of header information and data part
• Number of Links: I announced several OSPF

（3）—— Link data part ：

• —-COST value , This is me. ABR Go to this ASBR Of cost value

（4)—— How to view ：

show ip ospf database asbr-summary