[j-nsp] improving global unicast convergence (with or without BGP-PIC)

[adamv0025 at netconsultings.com]

> James Bensley
> Sent: Thursday, April 27, 2017 9:13 AM
> 
> It might be worth pointing out that on Cisco you need to enable PIC Core for
> PIC Edge to work at its best. PIC Core as already mentioned is just enabling
> the hierarchical FIB. So for your IGP / global routing table prefixes they will be
> covered by backup paths if they exist (backup path computed and installed
> into hardware FIB).
> 
Don't know about that, on Cisco Edge and Core functionality seems to be joined together. 

For instance in IOS or XE FIB hierarchy is enabled by default and can be disabled using: 
"cef table output-chain build favor memory-utilization" and re-enabled using "cef table output-chain build favor convergence-speed". 
In detail Convergence speed and indirection characteristics are enabled by default for the building of Cisco Express Forwarding table output chains (Since or beloved 12.2(33)SRA). 

The BGP PIC (Core) is configured using  "bgp additional-paths install". 
The BGP PIC (Edge+Core) feature is automatically enabled by the BGP Best External feature. 
When you configure the BGP Best External feature using the bgp advertise-best-external command, you need not enable the BGP PIC feature with the bgp additional-paths install command.  
The BGP PIC feature does not work with the BGP Best External feature. If you try to configure the BGP PIC feature after configuring the BGP Best External feature, you receive an error. 
So it's either Core or Core+Edge. 

In XR  cmd "advertise best-external" only advertises best external path and does not enable PIC on its own. 
You need to use "additional-paths selection" policy to calculate backup or enable PIC (Edge+Core) functionality. 
However the FIB hierarchy is enabled by default. 
Once again no distinction between Core and Edge. 


> For you VPNv4/VPNv6 stuff one must enable PIC Edge with advertise best
> external or add path etc. However enabling PIC Edge without PIC Core means
> that backup paths will be pre-computed but not programmed into hardware. 
Again, not sure how can you enable PIC Edge but not PIC Core on Cisco? 


> In Juniper land, does one need to activate indirect-next-hop before you can
> provide PIC Edge for eBGP vpn4/vpn6 routes?
> 
Nope, just load-balancing. 
And then protection under neighbour stanza. 

> Is indirect-next-hop enabled by default on newer MX devices / Junos
> versions?
> 
Yes. 


adam

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