Information Technology Reference
In-Depth Information
Foundation Summary
The Foundation Summary is a condensed collection of material that provides a convenient
review of key concepts in this chapter. If you are already comfortable with the topics in this
chapter, this summary will help you recall a few details. If you just read the Foundation Topics
section, this review should help solidify some key facts. If you are doing your final preparation
before the exam, these materials are a convenient way to review the day before the exam.
BGP Summary
The characteristics of BGP are summarized as follows:
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Interdomain routing protocol.
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Uses TCP port 179 to establish connections with neighbors.
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BGP4 implements CIDR.
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eBGP for external neighbors.
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iBGP for internal neighbors.
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Uses several attributes for decision algorithm.
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Uses confederations and route reflectors to reduce BGP peering.
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Peer Groups apply policies to a group of routers; Communities apply policies to a group
of networks.
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MED (metric) attribute between autonomous systems to influence inbound traffic.
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Weight attribute influences the path of outbound traffic from a single router, configured
locally.
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Local preference attribute influences the path of outbound traffic from an AS.
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Administrative Distance is 20 for eBGP and 200 for iBGP.
BGP Decision Algorithm
The BGP decision algorithm can be summarized as follows:
If no next hop, drop the path.
1
For internal path with synchronization, and the route is not in the IGP, drop the path.
2
Highest weight.
3
Highest local preference.
4
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