IGP metric attribute semantic dichotomy

[Lexi Winter]

Maria Matejka via Bird-users:
> In short, there are two different route attributes in BIRD 2:
 
> - The whole route's total metric from here to the destination,
>   if set explicitly by `igp_metric = N` in filters.
>   I.e., a generic alternative to protocol-specific IGP metrics
>   like `ospf_metric1` or `babel_metric`.

> - Metric of the route's part between here and `bgp_next_hop`,
>   determined by recursive next hop resolution. I.e., from 
>   that route which resolved the recursive next hop, the value
>   in the first meaning of `igp_metric` is taken and stored here.
 
> **How to name these two attributes better?**

may i suggest "igp_metric" for the first and "next_hop_igp_metric" for
the second?

i believe these names are clear and obvious to the administrator without
having to consult any documentation: igp_metric is the metric for this
route in this IGP, and next_hop_igp_metric is the metric for the route's
next hop in the underlying IGP.

"next_hop_igp_metric" also has the advantage of not having a
BGP-specific name (e.g., "bgp_nexthop_metric"); while it may currently
be used mostly for IBGP (and EBGP confederation) routes, it could
potentially be used by any routing protocol.