On 31/05/11 16:57, Gert Doering wrote:
In your case, I'd have the core/border routers do route-reflector functions
towards the customer-edge routers. Saves you having to do a full mesh
between all the customer-edge routers, and saves you from having to add
two more boxes (two! one RR is going to fail one day, and then your BGP
is broken).
If you mean saving from installing two additional routers just for RR,
then I agree core/border should be RR towards customer-edge routers.
btw in your scheme there is link between CR1 and CR2, what's point to
have such, if my customer is have bgp session with both there is no
chance packet could go to "worst path" and thus link between CR1 and CR2
redundant. Probably I miss some case scenario?
Well, it depends a bit how the connectivity between CR1 and CR2 is
built. If you have two independent switches there, the direct link is
not strictly needed.
AR1 and AR2 two independent switches at different racks. If I understood
you correctly. So to replicate that scenario both physical links from
AR1 and AR2 to CR2 should fail.
Still, it has the advantage that if these switches
should fail, CR1 and CR2 always are connected - otherwise you'll run
into some weird problems.
Imagine:
upstream upstream
| |
CR1 CR2
| \
| \
| \
AR1 AR2
now what happens if a packet comes in from upstream 2 to CR2? It will
have to be dropped -> black-holing. So if you have a direct link CR1-CR2,
you ensure that your network never partitions, even if switch(es) fail.
Perfect explanation, thanks for that case scenario.
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