Information Technology Reference
In-Depth Information
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Diverse administrative control
—BGP was designed to provide interconnection of
many diverse networks, all under different administrative control. An autonomous
system in BGP is an independently controlled unit. BGP's ability to define the scope
of administrative boundaries is actually an extension of policy control. BGP autono-
mous systems can be used to divide administrative control of a network.
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Handling large prefix counts
—BGP was designed to scale with the growth of the
global Internet routing table. Initially, this meant carrying only 10,000 prefixes.
However, the mechanisms on which BGP is built have allowed it to scale to carry
more than 200,000 prefixes in production networks and more than 500,000 in
laboratory tests. The number of prefixes that can be maintained is primarily limited by
memory.
BGP Weaknesses
Although BGP does have several benefits, you must also remember its weaknesses:
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Increased convergence time
—BGP does not react quickly to network changes and
is not optimized for fast convergence. Although the convergence time can be tuned,
BGP is slower than an IGP.
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Increased complexity
—BGP is not intended for use in lieu of an IGP. Rather, it is to
act in a complementary fashion with an IGP. With BGP acting in tandem with the IGP,
there are additional dependencies, which increase the network's complexity.
Protocol design, much like network design, is a series of trade-offs. When BGP was
designed, sacrifices had to be made to achieve the primary design goals. The sacrifices
made when BGP was designed are the very features that are taken for granted in IGPs.
NOTE
Keep in mind that adding BGP to the network is likely to increase the operational complex-
ity. This translates into additional knowledge requirements for the support staff and adds
complexity to the troubleshooting process.
Assuming that BGP is the appropriate solution, the rest of this chapter shows you how to
effectively design and implement a BGP routing architecture for enterprise networks.
Specifically, various architectures are explored for designing a BGP-based enterprise
network core.