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

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Date:	Wed, 24 Aug 2011 09:20:10 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	David Lamparter <equinox@...c24.net>
CC:	jhs@...atatu.com, jamal <hadi@...erus.ca>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Interface without IP address can route??

On 08/24/2011 09:15 AM, David Lamparter wrote:
> 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 :)

Ok..glad to know there are folks with even crazier setups than mine :)

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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