Information Technology Reference
In-Depth Information
Defining the Problem
The design process begins with accurately defining the problem. The following questions
help you lay the groundwork:
What specific problem am I trying to solve?
What is the root cause of the problem?
How will BGP resolve this problem?
Does BGP resolve the root cause or just resolve symptoms?
If BGP resolves only the symptoms, focus on addressing the actual root cause. Using BGP
to treat symptoms can allow the underlying problem to continue to grow. A common
example is the number of prefixes carried in the IGP.
If prefixes are assigned in an ad hoc manner that does not allow summarization, BGP can
provide a temporary patch, but the root of the problem needs to be addressed as well. A
proper numbering scheme that allows for efficient summarization should be developed and
deployed, even though renumbering a network is time-consuming and often difficult.
If the root cause is not treated, it might become a chronic problem, and it won't become any
easier to resolve as the network grows. A network should never be allowed to evolve in an
uncontrolled manner. Network expansion should be controlled growth that is consistent
with the well-defined and documented network architecture. If the network outgrows a
particular architecture, a new architecture should be developed, and continued expansion
should be based on this new architecture.
Determining the Solution
In determining if BGP is the appropriate solution, you must examine its strengths and
weaknesses. BGP is just one more tool that is at the disposal of network engineers and
architects. Deploying BGP is not a panacea, but it can help engineers resolve difficult policy
and scaling issues if used correctly. However, there are trade-offs.
BGP Strengths
The following BGP strengths are important in designing an enterprise network:
Routing policy control —BGP is not so much a routing protocol as a policy definition
tool. The BGP protocol does carry NLRI, which allows for routing functionality;
however, the main intent is to give the network administrator flexibility in defining
routing policy. This is in contrast to IGPs, where the main intent is to provide
reachability and fast reconvergence.
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