Bird-communities: mention that link latency community generally doesn't consider intra-AS latencies

James Lu commited 2023-03-04 13:05:59 -0800 commit b1d10f06f39b984623d91d520094697587c2df20

howto/Bird-communities.md

@@ -44,6 +44,8 @@ For example, if your peer is 12ms away and the link speed between you is 250Mbit

 Two utilities which measure round trip time and calculate community values automatically are provided, written in [ruby](https://github.com/Mic92/bird-dn42/blob/master/bgp-community.rb) and [C](https://github.com/nixnodes/bird/blob/master/misc/dn42-comgen.c).

+**Note: In general, the link latency metric only reflects the latency of the *immediate* link, and not the overall latency from following a path**. A route may traverse multiple internal routers once it enters an AS, and because this is invisible to BGP, it's best to treat latency values as informational only and not use them to make routing decisions.

+

 ```

 $ ruby bgp-community.rb --help

 USAGE: bgp-community.rb host mbit_speed unencrypted|unsafe|encrypted|pfs

...	...	@@ -44,6 +44,8 @@ For example, if your peer is 12ms away and the link speed between you is 250Mbit
44	44
45	45	Two utilities which measure round trip time and calculate community values automatically are provided, written in [ruby](https://github.com/Mic92/bird-dn42/blob/master/bgp-community.rb) and [C](https://github.com/nixnodes/bird/blob/master/misc/dn42-comgen.c).
46	46
	47	+*Note: In general, the link latency metric only reflects the latency of the immediate* link, and not the overall latency from following a path**. A route may traverse multiple internal routers once it enters an AS, and because this is invisible to BGP, it's best to treat latency values as informational only and not use them to make routing decisions.
	48	+
47	49	```
48	50	$ ruby bgp-community.rb --help
49	51	USAGE: bgp-community.rb host mbit_speed unencrypted\|unsafe\|encrypted\|pfs