Devil's Advocate - Segment Routing, Why?

Baldur Norddahl baldur.norddahl at
Sun Jun 21 10:45:28 UTC 2020

On Sun, Jun 21, 2020 at 9:56 AM Mark Tinka <mark.tinka at> wrote:

> On 20/Jun/20 22:00, Baldur Norddahl wrote:
> I can't speak for the year 2000 as I was not doing networking at this
> level at that time. But when I check the specs for the base mx204 it says
> something like 32 VRFs, 2 million routes in FIB and 6 million routes in
> RIB. Clearly those numbers are the total of routes across all VRFs
> otherwise you arrive at silly numbers (64 million FIB if you multiply, 128k
> FIB if you divide by 32). My conclusion is that scale wise you are ok as
> long you do not try to have more than one VRF with a complete copy of the
> DFZ.
> I recall a number of networks holding multiple VRF's, including at least
> 2x Internet VRF's, for numerous use-cases. I don't know if they still do
> that today, but one can get creative real quick :-).
Yes I once made a plan to have one VRF per transit provider plus a peering
VRF. That way our BGP customers could have a session with each of those
VRFs to allow them full control of the route mix. I would of course also
need a Internet VRF for our own needs.

But the reality of that would be too many copies of the DFZ in the routing
tables. Although not necessary in the FIB as each of the transit VRFs could
just have a default route installed.


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