Routing flaps, was Re: Ping flooding
Forrest W. Christian
forrestc at imach.com
Fri Jul 12 16:17:11 UTC 1996
On Fri, 12 Jul 1996, Paul Ferguson wrote:
> I'm sorry, but I'm afraid that you're missing the point here.
> In most larger ISP backbones, the behavior of their IGP is indeed
> visible to the public, since in most instances, most of the Internet
> traffic relies on the stability of these interior (an esoteric term)
> networks. Therefore, whether interior or exterior flap is really of
> no relevance in this context.
<This isn't intended to irritate, I just want to make sure I understand
Let me try a very simple example:
To Internet To Internet <-- Peering points or upstreams
'Point A' 'Point B'
| Router A |---| Router B |
| Router C | | Router D |
To Downstream To Downstream
Non-BGP (Static) Non-BGP (Static)
Routers A & B are running BGP to the outside world, and iBGP between them.
Routers C & D are 'defaulted' into A and B.
If the link between A&B dies the Exterior Routes will (and should) flap.
If the link between either A or B and the Internet dies, the Exterior
Routes will (and should) flap.
If the line between routers A&C or B&D or between either C or D and their
respective static downstreams die, there should be NO external route
flap. However, if C&D are incapable of 'Null0' routing, it may be
beneficial to run dynamic routing between A&C and between B&D so that
A&B discard packets instead of causing a routing loop. This "internal
routing flap" should not be visible to the outside world.
I think that's what I meant to say before. Sometimes I'm not too clear
about what I'm saying. If I've still missed the boat feel free to let me
-forrestc at imach.com
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