[c-nsp] add-path on XR

Sebastian Neuner neuner at belwue.de
Tue May 10 07:27:55 EDT 2022

Hi everyone,

I am currently looking at getting BGP info from routers for different 
purposes. The servers (iBGP, RR-client) should see more than just the 
best-path, so simply enable add-path for this neighbor, right?

On JunOS (where I have done something like this before) you can simply 
set the number of paths the neighbor should receive:

> set [...group/neighbor/afi...] add-path send path-count 6

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

So that looks like it enables the capability for all iBGP peers, and in 
the process resets all sessions? (yay, fun) But there is no 
configuration per neighbor. Am I missing something?

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?

Would configuring that still reset all iBGP neighbors? Or just the ones 
where the policy sets "path-selection" parameters?

And why is the documentation for those products of the last few years in 
general such a catastrophe?


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