[c-nsp] SXI3 strange issue, Loose mode uRPF jumps to strict by itself

[Jared Mauch]

On the SUP720/EARL7 unicast-rpf is a global setting on the device.

If someone changes *any* interface to strict, all interfaces with u-rpf enabled will change to strict.

- jared

On Jul 29, 2010, at 3:21 PM, bas wrote:

> Hi All,
> 
> Yesterday we had a strange issue.
> Our monitoring tool alerted that one of our boxes (SUP720-3BXL - 6506
> running SXI3) became unreachable.
> 
> When we logged in everything looked ok.
> BGP was up, OSPF was up and nothing special in logging.
> Still traffic had dropped to near zero.
> 
> With "debug ip cef drop" we immediately saw that traffic was dropped
> due to uRPF feature.
> All upstream interfaces had strict mode uRPF configured, before the
> problems started it was loose mode uRPF.
> 
> After manually changing them back too loose mode traffic was restored.
> 
> A couple of minutes before the problems started an engineer had
> configured a customer facing interface with strict mode uRPF.
> Apparently this configuration changed triggered a bug that caused
> upstream interface loose mode to be automagically turned to strict
> mode.
> 
> So, hereby a heads up. If your SXI3 boxes show strange behavior,
> quickly check uRPF.
> 
> Cya,
> 
> Bas
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