Border Gateway Protocol

Module Code: ELEE1157

Module Name: Network Routing Management

Lecturer: Seb Blair BEng(H) PGCAP MIET MIHEEM FHEA

Contents

  1. What is Border Gateway Protocol PT1
  2. What is Border Gateway Protocol PT2
  3. Autonomous System PT1
  4. Autonomous System PT2
  5. Autonomous System PT3
  6. BGP Friend or Competitor?
  1. Who Operates Autonomous Systems?
  2. Autonomous System Number
  3. External and Internal Border Gateway Protocol
  4. Breaking the Internet with Border Gateway Protocol
  5. Trust
ELEE1157 | Network Routing Management

Border Gateway Protocol

  • Border Gateway Protocol (BGP) is the postal system of the internet.

  • When a packet leaves your system to another system over the Internet, BGP is responsible for looking at all of the available paths that the outbound packet/data could travel, and picking the best route, which usually hopping between Autonomous Systems.

    • When you post a letter into a post box, the Royal Mail for example will process that piece of mail and will choose a fast, efficient route to deliver that item to its addresses recipient.
ELEE1157 | Network Routing Management

Autonomous Systems

So far we have looked at LANs and WANs, but the internet is made of billions and billions of network. To manage the size of the internet these billions of networks are broken up into hundreds of thousands of smaller networks, known as Autonomous Systems (AS). So each of these networks is essentially a large pool of routers run by a single organisation.

The Internet therefore is a network of networks

ELEE1157 | Network Routing Management

Border Gateway Protocol

So essentially, the BGP is the protocol that makes the Internet work by enabling data routing on the Internet.

  • When a user in Australia loads a website with origin servers in Canada, BGP is the protocol that enables that communication to happen quickly and efficiently.

Static content such as
images and files can
be cached on edge server

When a login request is made
dynamic data is requested so this
is stored on the origin server

ELEE1157 | Network Routing Management

Autonomous Systems

If we continue to think of BGP as a postal service of the Internet then the AS’s are like individual post office branches.

A town may have hundreds of mailboxes,
but the mail in those boxes must go through
the local postal office before being routed to another destination.

The internal routers within an AS are like
post boxes, they forward their outbound
transmissions to the AS, which then uses
BGP routing to get these transmissions to their destinations.

ELEE1157 | Network Routing Management

Autonomous Systems

The figure below illustrates a simplified version of BGP. In this version there are only six autonomous systems on the Internet. If AS1 needs to route a packet to AS3, it has two different options:

AS2 → AS3

AS6 → AS5 → AS4 → AS3

Now imagine that there are hundreds of thousands of AS’s and that hop count is only one part of a complex route selection algorithm. That’s the reality of BGP routing on the Internet.

ELEE1157 | Network Routing Management

BGP Friend or Competitor

  • AS must be kept up to date with information regarding new routes as well as obsolete routes.

  • This is done through peering sessions where each AS connects to neighbouring AS’s for the purpose of sharing routing information.

  • Using this information, each AS is equipped to properly route outbound data transmissions coming from within.

  • BGP routes sometimes take business considerations into account.

  • Autonomous Systems often charge each other to carry traffic across their networks, and the price of access can be factored into which route is ultimately selected.

ELEE1157 | Network Routing Management

Who operates BGP Autonomous Systems?

Autonomous Systems (AS) typically belong to Internet Service Providers (ISP) or other large high-tech organisations:

  • Tech Companies

  • Universities

  • Government agencies

  • and Scientific organisation

Each AS wishing to exchange routing information must have a registered Autonomous System Number (ASN)

ELEE1157 | Network Routing Management

Autonomous System number

Internet Assigned Numbers Authority (IANA) assigns ASNs to Regional Internet Registries (RIRs), which then assigns them to ISPs and networks.

ASNs are:

  • 16 bit numbers between 1 and 65534

  • 32 bit numbers between 131072 and 4294967294.

In of 2020, there were approximately 67,000 ASNs in-use worldwide. Now there are 110,000+ These ASNs are only required for external BGP.

ELEE1157 | Network Routing Management

External and Internal BGP

  • Routes are exchanged and traffic is transmitted over the Internet using external BGP or eBGP.

  • AS can route through their internal networks, which is known as internal BGP, or iBG.

  • AS can choose from a number of internal protocols to connect the routers on their internal network.

  • eBGP is like international shipping; there are certain standards and guidelines that need to be followed when shipping a piece of mail internationally.

ELEE1157 | Network Routing Management

BGP Hijacking

https://youtu.be/9NBv7lKrG1A

ELEE1157 | Network Routing Management

Trust

  • BGP hijacks happen because the route-sharing function of BGP relies on trust through which the AS implicitly trust the routes that are shared with them.

  • There have been proposals to remedy this, but it would every AS to simultaneously update their behaviour. Which would the require the coordination of hundreds of thousands of organisations and the temporary downtime of the entire Internet.

ELEE1157 | Network Routing Management