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66
website/blog/01-BGP.txt
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66
website/blog/01-BGP.txt
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TODO:
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eBGP/iBGP session
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Graphs
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/**********************************************/
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/* A no-bullshit guide to a bullshit protocol */
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/**********************************************/
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We can think of the Internet as a network of networks which are all connected in some way. We will refer to these networks as Autonomous Systems(AS) in this article.
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Now, how do we connect these AS's in a sane way? This is where BGP comes in. BGP, which stands for `Border Gateway Protocol`, enables different AS's to exchange information with each other, e.g. communicating with each other.
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There are three main challenges BGP has to solve:
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- Scalability: The Internet is BIG. BGP needs to scale well to be feasible in a large scale.
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- Privacy: Networks don't want to divulge internal topologies (topology = how a network is structured)
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- Policy enforcement: The Networks themselves need to have control over where to send and recieve traffic.
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Other protocols, like Link-Sate routing, do not solve these challenges.
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BGP's key concept, which it revolves about, is called *path-vector routing*, where it adertises the entire AS-level path.
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Now, what is an AS-level path? We'll get to that in a minute.
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Before that, why do we need even BGP? The problem is that sending data over the internet costs money. If we want to minimize the costs of sending data, we need to find routes which cost as little as possible. This is also why BGP is a "follow the money" protocol. Different ASes only connect with each other if they can save money that way.
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There are two policies we can use to define this routing:
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- Selection: Which path to use (only relevant for outbound traffic)
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- Export: Which path to advertise (only relevant for inbount traffic)
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TODO: add graphs here
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===============================================
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eBGP and iBGP
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===============================================
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BGP comes in two flavors: eBGP and iBGP.
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The e/i stands for external/internal
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External BGP sessions connect border routers in different ASes. These are therefore use to learn routes to external destinatons
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TODO: add graph
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Internal BGP sessions connect the routers in the same AS. These are used to split up externally-learned routes internally. These are tehn announces exernally(to other ASes) again, using eBGP sessions.
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BGP itself is a pretty simple protocol composed of four basic messages:
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- open: establish a BGP session (using TCP)
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- notification: report unusual conditions
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- update: inform neighbor of a new best route
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- can be a change or a removal of a best route
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- keepalive: inform neighbor that connection is alive
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update messages carry an IP prefix together with a set of attributes:
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/*********************/
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/* IP prefix */
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/*********************/
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/* Attributes */
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/* */
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/* */
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/* */
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/* */
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/*********************/
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There are four types of different attributes:
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- NEXT-HOP
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- AS-PATH
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- LOCAL-PREF
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- MED
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91
website/blog/posts/01.html
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91
website/blog/posts/01.html
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<!DOCTYPE html>
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<link rel="stylesheet" href="../../style.css" type="text/css">
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<html>
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<body>
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<div class="around">
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<div class="content">
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<pre style="display: inline;">
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TODO:
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eBGP/iBGP session
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Graphs
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/**********************************************/
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/* A no-bullshit guide to a bullshit protocol */
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/**********************************************/
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We can think of the Internet as a network of networks which are all connected in some way. We will refer to
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these networks as Autonomous Systems(AS) in this article.
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Now, how do we connect these AS's in a sane way? This is where BGP comes in. BGP, which stands for `Border
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Gateway Protocol`, enables different AS's to exchange information with each other, e.g. communicating with each
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other.
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There are three main challenges BGP has to solve:
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- Scalability: The Internet is BIG. BGP needs to scale well to be feasible in a large scale.
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- Privacy: Networks don't want to divulge internal topologies (topology = how a network is structured)
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- Policy enforcement: The Networks themselves need to have control over where to send and recieve traffic.
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Other protocols, like Link-Sate routing, do not solve these challenges.
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BGP's key concept, which it revolves about, is called *path-vector routing*, where it adertises the entire
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AS-level path.
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Now, what is an AS-level path? We'll get to that in a minute.
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Before that, why do we need even BGP? The problem is that sending data over the internet costs money. If we want
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to minimize the costs of sending data, we need to find routes which cost as little as possible. This is also why
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BGP is a "follow the money" protocol. Different ASes only connect with each other if they can save money that
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way.
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There are two policies we can use to define this routing:
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- Selection: Which path to use (only relevant for outbound traffic)
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- Export: Which path to advertise (only relevant for inbount traffic)
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TODO: add graphs here
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===============================================
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eBGP and iBGP
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===============================================
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BGP comes in two flavors: eBGP and iBGP.
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The e/i stands for external/internal
|
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External BGP sessions connect border routers in different ASes. These are therefore use to learn routes to
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external destinatons
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TODO: add graph
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Internal BGP sessions connect the routers in the same AS. These are used to split up externally-learned routes
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internally. These are tehn announces exernally(to other ASes) again, using eBGP sessions.
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BGP itself is a pretty simple protocol composed of four basic messages:
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- open: establish a BGP session (using TCP)
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- notification: report unusual conditions
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- update: inform neighbor of a new best route
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- can be a change or a removal of a best route
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- keepalive: inform neighbor that connection is alive
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update messages carry an IP prefix together with a set of attributes:
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/*********************/
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/* IP prefix */
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/*********************/
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/* Attributes */
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/* */
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/* */
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/* */
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/* */
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/*********************/
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There are four types of different attributes:
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- NEXT-HOP
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- AS-PATH
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- LOCAL-PREF
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- MED
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</pre>
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</div>
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</div>
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</body>
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</html>
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1
website/blog/posts/02.html
Normal file
1
website/blog/posts/02.html
Normal file
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@ -0,0 +1 @@
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JJ is is a new version control system, made to be compatible with git and _much_ less painful than it.
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