Foundation Summary

The "Foundation Summary" section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on your CCDA exam, a well-prepared CCDA candidate should at a minimum know all the details in each "Foundation Summary" before taking the exam.

The CCDA exam requires that you be familiar with the following topics covered in this chapter:

■ OSPFv2—The OSPF link-state routing protocol for IPv4

■ OSPFv3—OSPF link-state routing protocol for IPv6

■ IS-IS—The IS-IS link-state routing protocol

Table 11-6 summarizes the OSPF router types. Know how to identify these routers from a description or a diagram. These router types apply to both OSPFv2 and OSPFv3.

Table 11-6 OSPF Router Types

OSPF Router Type


Internal router

Router whose interfaces belong to the same OSPF area.


Router connected to more than one area. It generates summary LSAs.


Router that injects external routes into the OSPF protocol.

Backbone router

Routers with at least one interface connected to Area 0.

Table 11-7 summarizes OSPF stub network types. Remember which LSAs are not permitted in each stub type. These stub types apply for both OSPFv2 and OSPFv3.

Table 11-7 OSPF Stub Network Types

OSPF Area Stub Type


LSA Types Not Permitted

Stub area

No OSPF external LSAs

Type 5

Totally stubby

No OSPF external and summary LSAs

Type 3, Type 4, and Type 5


No OSPF external, Type 7 produced by NSSA

Type 5

Table 11-8 summarizes OSPFv2 LSA types. Understand which routers generate the LSA and what type of information each contains.

Table 11-8 OSPFv2 Major LSA Types

Type Code




Router LSA

Produced by every router. It includes all the router's links, interfaces, state of links, and cost. This LSA type is flooded within a single area.


Network LSA

Produced by every DR on every broadcast or NBMA network. It lists all the routers in the multiaccess network. This LSA type is contained within an area.


Summary LSA for ABRs

Produced by ABRs. It is sent into an area to advertise destinations outside the area.


Summary LSA for ASBRs

Originated by ABRs. Sent into an area by the ABR to advertise the ASBRs.


AS external LSA

Originated by ASBRs. Advertises destinations external to the OSPF AS, flooded throughout the whole OSPF AS.


NSSA external LSA

Originated by ASBRs in an NSSA. It is not flooded throughout the OSPF AS, only to the NSSA.

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