Ketan Talaulikar has entered the following ballot position for
draft-ietf-grow-bmp-bgp-rib-stats-16: Discuss
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DISCUSS:
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Thanks to the authors and the WG for this document.
Note: this ballot has been updated for v16 of the document. The
previous number
of points is retained. Points that have been addressed are deleted.
Please find below certain points that I would like to discuss.
<discuss-1> Semantics of routes, paths, primary, and backup.
Section 2 of this document says:
Primary route: A route to a prefix that is considered the best route
by the BGP
decision process [RFC4271] and actively used for forwarding traffic to
that
prefix. Backup route: A backup route is eligible for route selection,
but it is
not selected as the primary route and is also installed in the
Loc-RIB. It is
not used until all primary routes become unreachable. Backup routes
are used
for fast convergence in the event of failures.
Consider an BGP route for destination prefix x/y is a multipath:
x/y via BGP NH1 (path1) (best)
via BGP NH2 (path2) (multipath - say ECMP)
via BGP NH3 (path3) (backup)
via BGP NH4 (path4) (valid but not best/multipath/backup)
via BGP NH5 (path5) (invalid - for whatsover reason)
This is a single route. The best/multipath/backup/valid/invalid/etc are
qualifiers of its paths. Except for two stats that refer to paths
(stale and
suppressed), everything is referring to routes. I would like to
discuss the
semantics of route vs path. It seems to me like some of the stats are
for paths
and not routes.
In general, I think the use of the terms primary/backup which are
related to
forwarding plane aspects can be confusing. Instead, perhaps using
terms that
are more suitable for BGP Loc-RIB would be better? I've suggested some
of them
above for consideration. Also refer to
draft-ietf-grow-bmp-path-marking-tlv -
the terms of stats should be aligned across the BMP documents?
Furthermore, there is a wrong assumption that backup paths are only
activated
when all primary paths are down. This is very much implementation
dependent.
Some implementations have a 1:1 provisioning of primary/backup - where
the
backup would get used when its specific primary goes down - this draws
on the
FRR notion in the forwarding planes. Refer to the definition in
draft-ietf-grow-bmp-path-marking-tlv
These clarifications have implications on several of the stats as they
are
defined currently.
<discuss-2> Section 3 has the following text and Section 4 introduces
a table
that brings up an interesting aspect.
"This section defines different statistics type for Adj-RIB-In and
Adj-RIB-Out
monitoring type. Some of these statistics are also applicable to
Loc-RIB; refer
to Section 4 for more details."
For types 24 through 28, they are applicable for both Adj-RIB-In and
Loc-RIB.
How does one know what is being reported? Can this be clarified? Seems
like
this is the first document introducing such overloaded types but I
don't find
the reason why this is being done. There is also a sort of duplication
for same
stat being both global as well as per afi/safi - is there any guidance on
whether only one of them needs to be supported (this way avoiding the
race
conditions and discrepancies in their totaling)?
It is important to clarify these aspects if this is going to set a
precedent/guidance for other similar stats in BMP in future documents?
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