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Intermediate Topic 32 of 50 Computer Networks

BGP

Protocol exchanging routes between autonomous systems.

How it works

The Border Gateway Protocol is the path-vector routing protocol of the internet, exchanging reachability information between autonomous systems, the independently operated networks identified by AS numbers. Routers advertise prefixes along with the AS path, and each network applies policies, such as local preference and filters, to choose routes based on business relationships as much as shortest paths. It runs over TCP port 179.

Step-by-step walkthrough

  1. The Internet is many autonomous systems, each run by one organization.
  2. AS 100 announces its address prefixes to neighbours.
  3. AS 200 passes the route on, adding itself to the AS path.
  4. AS 300 compares paths using policy and path length.
  5. The chosen route sends traffic across ASes, and bad announcements can hijack traffic.

Where it is used

Internet service providers, cloud providers, content networks and large enterprises use BGP to connect to the internet and to each other. Anycast and traffic engineering also depend on it.

Common pitfall

BGP trusts what neighbors announce, so misconfigurations or hijacks can redirect or black-hole traffic for whole regions, as in several major outages. RPKI route origin validation, prefix filters and max-prefix limits improve safety. Convergence is slow and policy interactions are complex, so test changes carefully.

Where it fits in the course

BGP is topic 32 of 50 in Computer Networks, rated Intermediate. It follows RIP and OSPF. The next topic is VLANs.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Computer Networks quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is BGP?
Protocol exchanging routes between autonomous systems. It belongs to Computer Networks and is an intermediate-level topic.
Where do people use BGP?
Internet service providers, cloud providers, content networks and large enterprises use BGP to connect to the internet and to each other.
What is the most common mistake with BGP?
BGP trusts what neighbors announce, so misconfigurations or hijacks can redirect or black-hole traffic for whole regions, as in several major outages.
What should I learn before this topic?
Start with RIP and OSPF, the topic just before it in Computer Networks.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Computer Networks quiz.
Is BGP hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn BGP?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to BGP?
RIP and OSPF, VLANs, Routing Algorithms are closely connected. The full list is in the related topics section of this page.
What should I study after BGP?
Continue with VLANs, the next topic in Computer Networks.

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