Which Ethernet?

[das দাশ]

I have two ethernet cards, named eth0 and eth2 by the OS. And, one of
them connects with the dsl modem through pppoe. 'pppoeconf' detected it,
and connected it to Internet with ppp0. But, I cannot get which ethernet
card (0 or 2) is connected with the modem? Is there any way to know it?

This is the result of 'ifconfig -a':
<<<
dd at mahammad:~$ ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:A1:B0:09:0C:8F  
          inet addr:192.168.0.1  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST 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:1000 
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:17 Base address:0x4e00 

eth2      Link encap:Ethernet  HWaddr 00:E0:7D:89:F6:2F  
          inet addr:192.168.1.40  Bcast:192.168.1.255
Mask:255.255.255.0
          inet6 addr: fe80::2e0:7dff:fe89:f62f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3353 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3044 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:956667 (934.2 KiB)  TX bytes:291065 (284.2 KiB)
          Interrupt:16 Base address:0x2f00 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:200 (200.0 b)  TX bytes:200 (200.0 b)

ppp0      Link encap:Point-to-Point Protocol  
          inet addr:59.93.222.179  P-t-P:59.93.192.1
Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1
          RX packets:1087 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1053 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3 
          RX bytes:247099 (241.3 KiB)  TX bytes:75384 (73.6 KiB)


>>>