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:

quoted

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