Layer3 OSPF LSAP and Special Area Summary.

Today, SPOTO will summarize some knowledge of Layer3 OSPF LSAP and special area. SPOTO is committed to all kinds of technologies that are popular with the globe. I hope it is helpful for you.

Session 1 OSPF role summary

First, ABR

1. ABR in common area

Name: Inter-area router

Position: Responsible for routing information between different areas (LSA3)

Scope: ABR is the same as for the OSPF area (area).

2. ABR in the NSSA area

Name: Inter-area router

Position: Responsible for (LSA3) routing information transfer between different areas, and converting LSA7 to LSA5 (re)transferred from NSSA area to other areas

Scope: ABR is the same as for the OSPF area (area).

Second, ASBR

1. ASBR in common area

Name: External Area Border Router

Position: Responsible for external routing (LSA5) information transfer

Scope: ASBR is the same as for the OSPF area (area).

2. ASBR in the NNSA area

Name: External Area Border Router

Jobs: Responsible for routing (LSA5) routing information between different areas, and then converted to ALS5 by the ABR of the NSSA area to the non-NSSA area.

Scope: ASBR is the same as for the OSPF area (area).

Session 2 LSA summary

First, LSA1

Router Link, called Router LSA

Features: Each router in the same area sends

Content: Direct route to the router

Flood range: In this area, it cannot be transmitted out of the area because ABR will not be transmitted.

Second, LSA2

Net Link, called Network Router LSA

Features: Send by the DR router in the same area (BDR is not sent)

Content: The DR router summarizes all routes in the area (except for the direct route of LSA1)

Flood range: In this area, it cannot be transmitted out of the area because ABR will not be transmitted.

Third, LSA3

Summary Net Link, called the inter-area router LSA (note that it is not called summary routing)

Features: ABR generation and sending between the same area

Content: The routing information of the adjacent area announced by the ABR router in the area (the ABRs are usually ABRs of two or more areas)

Flood range: The area between the ABR and the B area is reddish so that the A area and the B area have a routing link to the opposite end.

Fourth, LSA5

External Link called the area external router LSA

Features: Generated by the ASBR of the OSPF common area boundary and declared into the OSPF area (used for the external route link redistributed into the OSPF area)

Content: The external route link information generated by the common area ASBR is displayed as OE route in the RIB.

Flood range: reddish throughout OSPF, regardless of the area

Displayed as OE route in the routing table

Five, LSA4

Summary ASBR Link, Router LSA called ASBR

Features: Produced by ABR in non-NSSA areas

Content: Declare to R-other, the routing entry to the ASBR of the NSSA area (how to get to the ASBR)

Flood range: reddish in the area connected to the ABR in the non-NSSA area

Sixth, LSA7

Type-7 AS External Link called the external router LSA of category 7.

Features: Generated by ASBR in the NSSA area

Content: Declare OSPF external (re-divided OSPF) routing link information in the NSSA area

Flood range: ABR reddened in the NSSA area to the ABR of the NSSA. After the ABR is converted to LSA5, it is reddened to other non-NSSA areas.

Displayed as an ON route in the routing table

Seven, LSA6, 8, 9-11

LSA6, multicast OSPF LSA

LSA8, OSPF LSA used by BGP

LSA9-11, OSPF LSA used by MPLS-VPN

Session 3 special area summary

First, area 0

Area0 is the core area of OSPF, the core point of OSPF's entire network.

The OSPF network area is a day-to-day network area, with area0 as the center of the flower, and other areas area1-65535 is the petals to build.

LSA1, 2, 3, 5, 7 are allowed in this area

Second, the general area

The OSPF petal must be directly connected to the area0 area. If it is not connected to area0, you need to connect the virtual link to the area0 area.

LSA1, 2, 3, 5, 7 are allowed in this area

Third, the stub area

The peripheral area of OSPF, the closed area, does not allow external routes to be stepped.

Only LSA1, 2, 3 are allowed in this area.

However, a default route is generated. The configuration method is that all Rs in the area are configured as stub routers.

Fourth, the total stub area

The complete stub area of OSPF, completely enclosed area, does not allow external routes to be stepped again and does not allow routing between OSPF areas.

Only LSA1, 2 are allowed in this area.

However, a default route will be generated. The configuration method is that all Rs in the area are configured as totally stub routers.

V. NSSA area

LSA4 and LSA5 do not allow LSA4 and LSA5 to enter the area in the non-pure stub area of the OSPF area. However, in order to learn the external routes, the LSA7 can be accessed.

Only LSA1, 2, 3, 7 are allowed in this area.

The default route will not be generated. If necessary, you can manually enable the configuration that generates the default route:

R3(config-router)#area 34 nssa default-information-originate Manually specify a default route in the NSSA area.

The configuration method is that all Rs in the area are configured as NSSA routers.

Sixth, totally NSSA area

The completely non-pure stub area of OSPF, the upgraded version of the total stub, does not allow LSA3, LSA4, and LSA5 to enter the area, but allows LSA7 to enter in order to learn external routes.

Only LSA1, 2, 7 are allowed in this area.

However, a default route is generated. The configuration method is that all Rs in the area are configured as totally NSSA routers.