Very old thread, but I was digging around and found it, so thought I'd
answer, in case no one did:
On 5/10/22 13:27, Sebastian Neuner wrote:
But on IOS XR, I can only find global options to enable the capability
and set a general limit for the number of paths, like this:
router bgp 65000
address-family ipv6 unicast
additional-paths send
maximum-paths ibgp 6
"maximum-paths" only applies to Multipath, not Add-Paths.
So that looks like it enables the capability for all iBGP peers, and
in the process resets all sessions? (yay, fun)
Add-Paths is a non-default capability. If it has not been previously
enabled, the session is torn down so it can be negotiated with the neighbor.
But there is no configuration per neighbor. Am I missing something?
To support the capability, that is at the AF level.
After IOS XR 7.3.1, per-neighbor level is supported for path selection.
But the capability remains at the AF level, AFAICT.
There are some knobs in the route-policy. I found stuff like
route-policy monitoring-out
set path-selection all advertise
But how does that work? Do all iBGP neighbors without "path-selection"
options in their out-policy continue to only receive the best path?
And the monitoring-servers receive "maximum-paths"-many paths?
It means that for any neighbors who are advertising their ability to
receive additional paths, you will be able to send them all available
paths with that policy.
Would configuring that still reset all iBGP neighbors? Or just the
ones where the policy sets "path-selection" parameters?
No. Path selection policies and their advertisement does not reset BGP
sessions. BGP sessions are only reset when you need to negotiate
Add-Path capability exchange.
And why is the documentation for those products of the last few years
in general such a catastrophe?
I'm guessing most people don't use Add-Paths as much as they do
Multipath, so perhaps why.
Mark.
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