Primary route confusion

[Kenth Eriksson]

On Fri, 2018-09-21 at 15:52 +0200, Ondrej Zajicek wrote:
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> On Fri, Sep 21, 2018 at 11:58:41AM +0000, Kenth Eriksson wrote:
> > So the preference value in BIRD is not the same as administrative
> > distance? I believe both Juniper and Cisco treats lower preference
> > value / administrative distance value as a more preferred route.
> > 
> > 
> > 
https://www.juniper.net/documentation/en_US/junos/topics/reference/general/routing-protocols-default-route-preference-values.html
> > 
> > Is preference value inverted in BIRD?
> 
> It has same position/usage as administrative distance in
> Juniper/Cisco,
> but it is inverted (lower is better) relative to them.
> 
> Generally, for property called 'metric' or 'distance' it makes sense
> that
> lower is better, while for 'preference' it makes sense that higher is
> better, it this sense Cisco and BIRD have it in natural way, while
> Juniper
> has it inverted.
> 

I believe Cisco uses administrative distance, which is inverted from
how BIRD has defined its preference  value. This wiki article has a
table for Cisco AD.

https://en.wikipedia.org/wiki/Administrative_distance

I still think BIRD confuses a user here (at least me). Consider the
following route in BIRD;

172.20.4.41/32       unicast [ospf1 2018-09-21] * I (110/50)
[172.20.4.41]
	via 172.20.4.41 on p1-1-1-1-2

The preference value is 110 and higher is better. The OSPF metric is 50
and lower is better. If BIRD were to use administrative distance
instead of preference, then you know that lower is always better. 

Any plans to support AD?

Thanks,
Kenth