On Sun, Apr 3, 2016 at 6:17 PM, Mark Tinka <mark.tinka@seacom.mu> wrote:
On 31/Mar/16 10:12, magicboiz@hotmail.com wrote:
My questions are:
1. What could happen in the case of total failure in the redundant leased lines? Black hole routing between POPs?
If you have redundant backhaul that completely fails, you've got real problems.
However, if that does happen, any traffic coming into each individual PoP destined for users in the other PoP will fail. Only traffic terminating for customers at that PoP will succeed.
so (as bill points out) plan to localize subnets to each pop. (do not number customers in pop1 in the same /24 as customers in pop2)
2. What are the best design methods to avoid this scenario?
Work on your backhaul.
Originate specific routes that cover customers present in each PoP, with the aggregate as a backup route.
You can run a tunnel across the Internet to simulate a backbone between both PoP's, using your side of your upstream's IP addresses as the tunnel end-point. Not elegant, but keeps you up.
be aware of gre / ip-in-ip forwarding limitations
2.1: adding a third POP creating a triangle? What if a POP looses connection with the other two POPs at the same time? Another black hole?
Your fixation on a complete backhaul outage is interesting.
Purchase backhaul from different service providers to increase your chances of uptime.
different providers, different entrance facilities in the building(s), different conduits out of the area... and hope that somewhere along the path providerA and B didn't share conduit or capacity-swap you to a single path :)
2.2: requesting another prefix and allocating 1:1 prefix:POP, so in the scenario each POP only would announce its prefix to the upstreams?
See above re: originating more specific routes based on the customers you have at each PoP.
2.3: other?
Work harder on your backhaul.
Yes, bad things can happen, and they do happen. But more than likely, if a 3-PoP network loses all connectivity from each other, I think routing will be a much smaller problem to solve in the grand scheme of things.
Mark.