netdev - Re: Interface without IP address can route??

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110824161557.GC611458@jupiter.n2.diac24.net>
Date:	Wed, 24 Aug 2011 18:15:57 +0200
From:	David Lamparter <equinox@...c24.net>
To:	Ben Greear <greearb@...delatech.com>
Cc:	jhs@...atatu.com, jamal <hadi@...erus.ca>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Interface without IP address can route??

On Wed, Aug 24, 2011 at 06:24:54AM -0700, Ben Greear wrote:
> On 08/24/2011 06:01 AM, jamal wrote:
> > It makes sense to behave this way.
> > IPv4 addresses are owned by the system not interfaces.
> > If you want to control the forwarding behavior, control ARP so it doesnt
> > respond on the interfaces with no IP.

I agree.

> I understand your argument about IPs being owned by system instead of
> interface, but I think it's the wrong behaviour in this case.  Can
> you think of any case where this behaviour actually helps?

It's used for oddball /32 setups at server hosting farms that look like:
      /--- eth0, no ip ---- server 0.1.4.5/32, default via 0.1.2.3
router --- eth1, no ip ---- server 0.1.6.7/32, default via 0.1.2.3
      \--- eth2, no ip ---- server 0.1.8.9/32, default via 0.1.2.3
   \- eth3: 0.1.2.3/28 - to rest of internet

The general idea is to a) conserve IPs and b) not renumber servers even
when they move, so you end up with random scattered /32s on the servers
and the router has no sensible IP.

> Either way, it appears I can work around this by explicitly disabling
> forwarding for this particular interface.

I was about to suggest exactly this :)


David

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html