Simon Marsh
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65 lines
2.7 KiB
Markdown
65 lines
2.7 KiB
Markdown
---
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title: "BGP Communities"
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geekdocDescription: "BGP communities used in the network"
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weight: 50
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---
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This page describes the use of BGP communities within the network.
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## DN42 Communities
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[DN42 Communities](https://dn42.net/howto/Bird-communities) are applied both internally and externally, and are used to influence the [Routing Policy](/home/routing-policy).
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|Community |Description|
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|:---|:---|
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|( 64511 : 0 < x < 21 ) | Max latency |
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|( 64511 : 20 < x < 30 ) | Min bandwidth |
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|( 64511 : 30 < x < 35 ) | Min encryption |
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|( 64511 : 40 < x < 54 ) | Route Origin |
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## Well Known BGP Communities
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The following well known communities are implemented.
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|Community |Description|Action|
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|:---|:---|:---|
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| ( 65535 : 65281 ) | No Export | Prefix should not be exported outside of AS4242422601 |
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| ( 65535 : 65282 ) | No Advertise | Prefix should not be exported to any peers |
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| ( 65535 : 65283 ) | Local-AS | Prefix should not be exported outside of region |
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## burble.dn42 Specific Communities
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burble.dn42 implements [large BGP communities](http://largebgpcommunities.net/), with [ISO 3166-1 / UNSD](https://en.wikipedia.org/wiki/ISO_3166-1) country, and [UNSD](https://unstats.un.org/unsd/methodology/m49/) region codes.
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### Informational Communities
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|Community |Description|
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|:---|:---|
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| ( 4242422601 : 120 : _host code_ ) | Route learned on this host |
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| ( 4242422601 : 130 : 1 ) | Route is a direct peer |
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| ( 4242422601 : 140 : _DN42 region_ ) | Route learned in this DN42 region |
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### Internal Ghost Route Protection
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In a large network like burble.dn42 it can take some time for route updates
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to be distributed and for the network to settle following changes. As changes
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ripple through the network it can create a cascade of ghost updates, each with
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an increasing internal path length, or adjusted latency metric. Worse the
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cascade of updates can also be re-distributed to peers, creating a significant
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multiplier for the number of updates from a single change.
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To protect against ghost routes, a community is used to track how many internal
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hops a route has. In a fully meshed network like burble.dn42, a genuine route should
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never have more than two internal hops, so an export filter is used to prevent
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distribution of longer paths.
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|Community |Description|
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|:---|:---|
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| ( 4242422601 : 100 : 1 ) | Added on first internal re-distribution |
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| ( 4242422601 : 100 : 2 ) | Added on second re-distribution and prevents further re-distribution within burble.dn42 |
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The ( 4242422601 : 100 : x ) communities are not exported to peers.
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