netdev - Re: [PATCH net-next-2.6] ipv4: sysctl to block responding on down interface

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Date:	Mon, 28 Jun 2010 23:09:02 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH net-next-2.6] ipv4: sysctl to block responding on down interface

Eric Dumazet <eric.dumazet@...il.com> wrote on 2010/06/28 21:42:01:
>
> Le lundi 28 juin 2010 à 21:03 +0200, Joakim Tjernlund a écrit :
> > Stephen Hemminger <shemminger@...tta.com> wrote on 2010/06/11 17:48:54:
> > >
> > > When Linux is used as a router, it is undesirable for the kernel to process
> > > incoming packets when the address assigned to the interface is down.
> > > The initial problem report was for a management application that used ICMP
> > > to check link availability.
> > >
> > > The default is disabled to maintain compatibility with previous behavior.
> > > This is not recommended for server systems because it makes fail over more
> > > difficult, and does not account for configurations where multiple interfaces
> > > have the same IP address.
> > >
> > > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> >
> > Ping David et. all?
> > I too want this.
>
> You probably missed David reply
>
> http://permalink.gmane.org/gmane.linux.network/164494

Sure did, don't know how that happened, sorry.

Reading David's reply I do wonder about the current behaviour. Why
is it so important to keep responding to an IP address when the
admin has put the interface holding that IP address into administratively
down state? I don't think the weak host model stipulates that it must be so, does it?

To me it "ifconfig eth0 down" means not only to stop using the I/F but
also any IP address associated with the I/F. I was rather surprised that
it didn't work that way. I don't see any way to make Linux stop responding to
that IP other that removing it completely from the system, which is rather
awkward.

Note, I don't mean that the same should be applied for the No Carrier case, just
ifconfig down.

 Jocke

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