[j-nsp] Interconnecting spines in spine & leaf networks [ was Re: Opinions on fusion provider edge ]

[Gert Doering]

Hi,

On Thu, Nov 15, 2018 at 10:22:51AM -0600, Aaron1 wrote:
> Well, I???m a data center rookie, so I appreciate your patience
> 
> I do understand that layer 2 emulation is needed between data centers, if I do it with traditional mechanisms like VPLS or l2circuit martini, I???m just afraid if I make too many connections between spine and leaves that I might create a loop

Since these connections are all *routed*, the routing protocol takes care
of loops.  There is no redundant L2 anything (unless you do LACP links,
but then LACP takes care of it) that could loop.

The "user-visible layer2 network" stuff emulated via VXLAN, MPLS, ...
might form loop, so how you attach downstream L2 "infrastructure" will pose 
some challenges - but this is totally independent from the leaf/spine
infra.

> However, I???m beginning to think that EVPN may take care of all that stuff, again, still learning some of the stuff that data centers due

EVPN is, basically, just putting a proper control-plane on top of MPLS
or VXLAN for "L2 routing" - put your MAC addresses into BGP, and it will
scale like hell.

ISPs I've talked to like EVPN, because "this is BGP, I understand BGP".

Enterprise folks find EVPN scary, because "this is BGP, nobody here knows
about BGP"... :-)  (and indeed, if BGP is news to you, there are way too
many things that can be designed poorly, and half the "this is how you do
a DC with EVPN" documents design their BGP in ways that I wouldn't do...)

gert

-- 
"If was one thing all people took for granted, was conviction that if you 
 feed honest figures into a computer, honest figures come out. Never doubted 
 it myself till I met a computer with a sense of humor."
                             Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany                             gert at greenie.muc.de
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