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Re: Query on Netlink sockets on debian etch

On Fri, 2009-10-02 at 23:40 +0530, sathya sai wrote:
> But, when I reconfigure my network interface with the below ifconfig
> command, I am shocked that the above netlink program is giving me two
> notifications with RTM_NEWADDR (new address being added to an
> interface)
> I am not sure why the second ifconfig command gives me the two
> RTM_NEWADDR netlink notifications?
> ifconfig eth0 inet 0
> ifconfig eth0 inet netmask
> To analyse further on this, I then changed the second ifconfig to as
> in below(removed the netmask part),
> ifconfig eth0 inet
> Now I am getting only one RTM_NEWADDR netlink notification from the
> kernel.(although the netmask and broadcast address as been assigned to
> the default address by the kernel).
> Could you please help me out by answering why with my prior netlink
> command the debian kernel was triggering  two RTM_NEWADDR
> notifications.

If I run:
    strace ifconfig eth0 inet netmask
it shows me:
    ioctl(4, SIOCSIFADDR, 0xff97ca88)       = 0
    ioctl(4, SIOCGIFFLAGS, {ifr_name="eth0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_MULTICAST}) = 0
    ioctl(4, SIOCSIFFLAGS, 0xff97c98c)      = 0
    ioctl(4, SIOCSIFNETMASK, 0xff97ca88)    = 0

So the address and netmask configuration are two separation operations
that are notified separately.


Ben Hutchings
Who are all these weirdos? - David Bowie, about L-Space IRC channel #afp

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