Simon Marsh
556c837aa9
All checks were successful
continuous-integration/drone/push Build is passing
53 lines
2.5 KiB
Markdown
53 lines
2.5 KiB
Markdown
---
|
|
title: "Routing Policy"
|
|
geekdocDescription: "Description of the network routing policy"
|
|
weight: 40
|
|
---
|
|
With a global network and multiple peers, the burble.dn42 network typically has many alternative route paths for reaching a particular destination. The routing policy aims to keep route selection sane, and avoid sending traffic outside of a region where possible.
|
|
|
|
## Policy Objectives
|
|
|
|
1. Direct routes for prefixes belonging to a peer should be given the highest priority.
|
|
- So that traffic to peer networks is routed over the burble.dn42 network directly to the peer and not via an external 3rd party
|
|
3. Routes to the anycast prefixes should be prioritised through stable, low latency peers.
|
|
- To ensure stability within the network and provide good routes for well known destinations (e.g. DNS and the DN42 wiki)
|
|
5. Where prefixes are tagged with a DN42 region, they should be routed locally or within the burble.dn42 network.
|
|
- To avoid sending traffic across regions when this could have been avoided.
|
|
- The AS path length is also increased between regions to pursuade external routers to also prefer local hosts.
|
|
7. Prioritise by shortest path, then lowest latency
|
|
|
|
## Policy Implementation
|
|
|
|
### bgp local_pref
|
|
|
|
The local_pref for routes is set on entry, and then propogated across the whole network. This forces the
|
|
network to prefer routes that, where possible, send traffic through the burble.dn42 network to a local peer,
|
|
rather than sending cross regional traffic through external peers (aka
|
|
[Cold Potato Routing](https://en.wikipedia.org/wiki/Hot-potato_and_cold-potato_routing)).
|
|
|
|
|Local Pref | Route Class |
|
|
|:---|:---|
|
|
| 3000 | burble.dn42 dynamic / anycast routes |
|
|
| 2000 | burble.dn42 internal networks |
|
|
| 1000 | Peer networks (AS path len = 1) |
|
|
| 500 | Route received in same DN42 region as it originated |
|
|
| 100 | Default |
|
|
|
|
### bgp med
|
|
|
|
The med attribute is used to implement a latency based metric across the network. Scripts are used
|
|
to gather the latency between nodes (using ping) and this is then incorporated in to the ansible
|
|
scripting that generates the peer configuration for the internal mesh. The peer configuration
|
|
sets the med to be the latency in ms between nodes (in milliseconds * 10). A penalty of 500 is added
|
|
for each hop to encourange direct routing between nodes.
|
|
|
|
```
|
|
med = (latency between nodes in ms * 10) + (500 per hop)
|
|
```
|
|
|
|
The med metric is exported to external peers to help them decide how to route traffic to the burble.dn42
|
|
network.
|
|
|
|
|
|
|