Lecture 2: Intro to BGP Flashcards

1
Q

What is Border Gateway Protocol, (BGP)?

A

The protocol responsible for managing how traffic transits from AS to AS

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2
Q

What is the primary purpose of BGP?

A

Allow routing systems to share information on what resources
can be reached and where

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3
Q

Which protocol and port is used to send BGP information?

A

BGP information is sent via TCP (Transmission control protocol) using port 179

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4
Q

How does BGP work?

A
  • Router sends out updates of currently available routes (advertisements)
  • Other routers use the advertisements to update their own mappings
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5
Q

What do Path-Vector Routing Protocol do?

A

Define a route as the collection of autonomous systems that must be travelled from source to destination

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6
Q

What is the AS-Path?

A

The AS-Path describes a given path from one AS to another

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7
Q

How is the AS-Path generated?

A

An AS re-advertises routes it has received,and adds it’s own AS to the AS-PATH variable

The AS-PATH variable then identifies each AS that will be transited through for the route

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8
Q

What is the purpose of the AS-Path?

A

To prevent loops in the
routing algorithm

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9
Q

What is AS-Path Prepending?

A

AS adds its own AS multiple times to the AS-Path to discourage people from using it

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10
Q

How do routers learn about their neighbours through BGP?

A
  • BGP sends out hello messages
  • BGP maintains regular communication to check if the neighbour is still alive
  • BGP allows advertisements to be sent/received as routes change
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11
Q

What are the 3 core activities in a BGP routing system.

A
  1. Listen for paths from internal and
    external BGP sources
  2. Pick the best path and put it into the routing table
  3. Advertise the best path to your neighbours
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