[c-nsp] LDPv6 Census Check

Thu Jun 11 18:50:11 UTC 2020

On 6/11/20, 1:19 PM, "Saku Ytti" <saku at ytti.fi> wrote:

    On Thu, 11 Jun 2020 at 19:49, Phil Bedard <bedard.phil at gmail.com> wrote:

    > As for normal v6 forwarding, the way most higher speed routers made recently work there is little difference in latency since the encapsulation for the packet is done in a common function at the end of the pipeline and the lookups are often in the same memory space.  NPUs are also being built today with enough on-package memory to hold larger routing tables.   Whether a packet has to be buffered on-chip vs. off-chip has a much larger impact on latency/PDV than a forwarding lookup.

    On-package is not important, on-chip or off-chip is what matters, i.e.
    do you eat SERDES to connect memory or not.

[pmb] 
Sorry meant to say on-die, not on-package.  

Typically the time it takes to do those lookups are built into the system specs to attain the performance you need with deterministic latency within a certain bounds.  There are certainly corner cases where you make tradeoffs, especially now that single NPUs are 10+ Tbps, but it's not really an MPLS vs. IPv4 vs. IPv6 thing.  The other key is to do those types of accesses in a single pass, not traverse multiple hierarchy levels or do multiple operations.  If you are tunneling then the table for any of those types is going to small on a mid-point router.  