Backbone router

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

A backbone router is an OSPF router with at least one interface in the backbone area.

A backbone router is an OSPF router with at least one OSPF-enabled interface in area 0, the backbone area. Area 0 provides the connection point for non-backbone areas. section 18.1.2 section 18.5

Distinguish backbone routers from related OSPF router types:

• An internal router keeps all OSPF-enabled interfaces in one area; it can also be a backbone router when that area is area 0. section 18.1.2
• An area border router connects one or more areas to area 0, so every ABR is also a backbone router, but not every backbone router is an ABR. section 18.1.2
• An autonomous system boundary router connects OSPF to external networks and may independently be a backbone, internal, or area border router. section 18.1.2

Figure 18.2 A multi-area OSPF network consisting of four areas. Area 0 is the backbone area to which other areas must connect. Areas 1, 2, and 3 are non-backbone areas, and traffic between them must pass through area 0.

Use the multi-area topology to identify area 0, the backbone routers, and the required paths between non-backbone areas. section 18.1.2

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Defines the classification and contrasts it with internal routers, ABRs, and ASBRs without describing configuration commands.

Examples

Uses a four-area topology and identifies R1 through R5 as backbone routers, with R3 through R5 also serving as ABRs.

What it assumes

Assumes familiarity with OSPF areas while defining area 0 and related router categories.

What you can do after

Evaluate OSPF diagrams and classify routers by their area 0 interfaces and relationships to other areas.

How it connects

Connects backbone routers with OSPF areas, area 0, internal routers, area border routers, and autonomous system boundary routers.

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Related concepts

• OSPF area border routerincludes · An OSPF area border router connects one or more nonbackbone areas to the backbone area.
• backbone areaconfigures · The OSPF backbone area is area 0, the central area through which traffic between non-backbone areas passes.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.