Re: Interface without IP address can route??

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.

ARP is already controlled, but interface was effectively promisc,
so it received packets anyway.  This allows me to bridge packets
in user-space using packet sockets.

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?

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

Thanks,
Ben

cheers,
jamal
On Tue, 2011-08-23 at 17:20 -0700, Ben Greear wrote:

quoted

I just noticed on a 3.0.1 kernel that the system is routing packets
received on an interface without an IP address. (I was trying to use the
interface in a user-space wifi_station-to-wired bridge application).

[root@lf0301-demo1 lanforge]# cat /proc/sys/net/ipv4/conf/sta1/forwarding
1
[root@lf0301-demo1 lanforge]# ifconfig sta1
sta1      Link encap:Ethernet  HWaddr 00:03:2D:12:16:0D
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:85248 errors:0 dropped:0 overruns:0 frame:0
            TX packets:1419 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:67423391 (64.2 MiB)  TX bytes:1087581 (1.0 MiB)


Seems that older stock kernels have forwarding set for interfaces without
IP addresses too, so maybe it's always been this way...

Anyway, I can add some logic to my config to explicitly disable
routing for interfaces w/out IP address, but it seems to me that
it should automatically not route packets received on an interface
that had no IP address on it..

Thanks,
Ben

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Ben Greear [off-list ref]
Candela Technologies Inc  http://www.candelatech.com