Subject: Interface without IP address can route??

From: Ben Greear <[email-masked]>
Date: Tue, 23 Aug 2011 17:20:29 -0700

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

-- 
Ben Greear <[email-masked]>
Candela Technologies Inc  http://www.candelatech.com