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.
| Routes Accepted | Memory and CPU | Path Selection |
|---|---|---|
| Default routes from each ISP | Low | Route to the nearest BGP router. |
| Some routes plus default from ISPs | Medium | Take the router receiving specific path if offered; otherwise, route to nearest BGP router. |
| All routes from ISPs | High | Always 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
