Ccna routing and Switching Complete Study Guide

Protocol Comparison and Overview

Because BGP is the first exterior gateway protocol we’ve encountered, I’ll briefly compare it 

to a more familiar interior gateway protocol, like OSPF, so that we can put its features into 

context. After that comes a brief overview of BGP so that you can quickly become aware of 

its main capabilities.

Just to clarify things, with this comparison, I’m not implying that OSPF could be a 

substitute for BGP. In fact, there are a number of reasons that BGP is far better suited as an 

exterior gateway protocol than OSPF. For example, the requirement that all OSPF areas be 

connected to area 0 simply doesn’t allow OSPF to scale to the size required by the Internet. 

Thousands of areas would have to connect to area 0, overwhelming it with route updates. 

In addition, OSPF uses a metric based on bandwidth, but in the context of the Internet, 

routing decisions are also based on political and business issues. OSPF does not have any 

mechanism to modify path selection based upon factors such as interconnection agreements 

between Internet service providers.

Although BGP can be thought of as just another routing protocol, the differences 

between it and protocols like OSPF are significant enough to catapult it into an entirely dif-

ferent category. Table 21.1 contains a comparison of BGP and OSPF.

TA b l e   21.1     Comparison of BGP and OSPF