[ntp:hackers] Correctly detecting interfaces

Philip Prindeville philipp_subx at redfish-solutions.com
Fri Jul 12 03:00:04 UTC 2013

I was looking at lib/isc/unix/ifiter_ioctl.c (et al) works:

        if ((ifa->ifa_flags & IFF_UP) != 0)
                iter->current.flags |= INTERFACE_F_UP;

and thinking that the semantics aren't exactly right. This checks for the interface being configured, but not necessarily "up" (i.e. having carrier).  I'm thinking a more precise semantic might be:

        if ((ifa->ifa_flags & (IFF_UP | IFF_RUNNING)) != (IFF_UP | IFF_RUNNING))
                iter->current.flags |= INTERFACE_F_UP;

which requires the interface to be both configured and be active at the physical layer.

Anyone have an argument against this proposal?


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