Foundation Summary

The Foundation Summary provides a convenient review of many key concepts in this chapter. If you are already comfortable with the topics in this chapter, this summary might help you recall a few details. If you just read this chapter, this review should help solidify some key facts. If you are doing your final prep before the exam, the following lists and tables are a convenient way to review the day before the exam.

The key features of BGP include the following:

  • BGP is an enhanced path vector protocol that supports VLSM, CIDR, and summarization.

  • BGP creates and maintains connections between peers, using the destination TCP port 179 and keepalives, respectively.

  • BGP path attributes allow granularity in path selection.

  • BGP has its own table. BGP routes appearing in the routing table are judiciously selected from the BGP table.

Table 14-3 summarizes the different approaches to obtaining routing information from the Internet.

Table 14-3. Receiving Routing Updates from Multiple ISPs
Routes AcceptedMemory and CPUPath Selection
Default routes from each ISPLowRoute to the nearest BGP router.
Some routes plus default from ISPsMediumTake the router receiving specific path if offered; otherwise, route to nearest BGP router.
All routes from ISPsHighAlways take the most direct path.

BGP cycles through five states as it runs:

  • Idle— Searching for neighbors

  • Connect— TCP three-way handshake complete with neighbor

  • Open Sent— BGP Open message has been sent

  • Open Confirm— Response received

  • Established— BGP neighborship is established