[ASL] ip address problem

[Dan L. <da...@st...>]

libASL users,

I am having a strange problem with packets getting sent from an IP address 
that is assigned to a network interface on my machine even when it is down.

My configuration is as follows:

eth0 - wired ethernet, configured for 192.168.1.140
eth1 - 802.11b card, configured for 10.1.1.2



Ok, I can explicitly bring down the eth0 interface with `/sbin/ifconfig eth0 
down`. Now, eth0 does not appear in the list of interfaces when I do an 
`/sbin/ifconfig`. Then I ping some address as follows:

# ping 10.2.3.4

[root@localhost libASL]# ping 10.2.3.4
PING 10.2.3.4 (10.2.3.4) from 10.1.1.2 : 56(84) bytes of data.
From 10.1.1.2 icmp_seq=1 Destination Host Unreachable
From 10.1.1.2 icmp_seq=2 Destination Host Unreachable
From 10.1.1.2 icmp_seq=3 Destination Host Unreachable

--- 10.2.3.4 ping statistics ---
4 packets transmitted, 0 received, +3 errors, 100% loss, time 3028ms



Ok, thats what I want. Note that the ping is coming from 10.1.1.2 (my wireless 
interface) which is what I want.


Now I start up my ad-hoc routing daemon on eth1. I do a `/sbin/ifconfig`:

[root@localhost libASL]# /sbin/ifconfig
eth1      Link encap:Ethernet  HWaddr 00:02:2D:05:58:22
          inet addr:10.1.1.2  Bcast:10.255.255.255  Mask:255.0.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24 errors:1 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:0 (0.0 b)  TX bytes:3200 (3.1 Kb)
          Interrupt:5 Base address:0x100

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:58 errors:0 dropped:0 overruns:0 frame:0
          TX packets:58 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:5610 (5.4 Kb)  TX bytes:5610 (5.4 Kb)

tun       Link encap:Point-to-Point Protocol
          inet addr:127.0.0.2  P-t-P:127.0.0.2  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:10
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)


Note the tun interface is up as well as the wireless interface, but not eth0.

Now I try doing the same ping that I did before. I expect the result to be the 
same, except that I get activity on the ASL socket letting my routing daemon 
know of a route request. Here is the ping:


[root@localhost libASL]# ping 10.2.3.4
PING 10.2.3.4 (10.2.3.4) from 192.168.1.140 : 56(84) bytes of data.

--- 10.2.3.4 ping statistics ---
4 packets transmitted, 0 received, 100% loss, time 3014ms


There it is. I do get the activity on the ASL socket, but as you can see, the 
ping is from "192.168.1.140", which is the IP of eth0, which is down. This 
obviously causes a problem because the routing daemon thinks its IP is 
"10.1.1.2" and won't think this request for a route was generated locally.

Does anyone have any reason why this happens? Is this an issue with libASL or 
the way I am doing something in my routing daemon?