Two interfaces on the same network

[AL Chane]

Rodolfo J. Paiz ??:
> At 12:08 6/9/2004, Al wrote:
> 
>> I didn't set default gateway (if that's what you meant "default route")
>>
>> I just bring up two interfaces with:
>> >ifconfig eth0 172.20.1.30 netmask 255.255.255.0
>> >ifconfig eth1 172.20.1.31 netmask 255.255.255.0
>>
>> that's it. no more route or other commands.
> 
> 
> So as root:
> 
> # ip addr show
> # ip route show
> # route -n
> 
> What do those commands show?
> 
>
[root at AL sbin]# ./ifconfig
eth0      Link encap:Ethernet  HWaddr 00:01:29:4C:06:46
           inet addr:172.20.1.30  Bcast:172.20.1.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:566 errors:0 dropped:0 overruns:0 frame:0
           TX packets:464 errors:12 dropped:0 overruns:0 carrier:24
           collisions:0 txqueuelen:100
           RX bytes:46725 (45.6 Kb)  TX bytes:39630 (38.7 Kb)
           Interrupt:11 Base address:0x7000

eth1      Link encap:Ethernet  HWaddr 00:02:B3:A3:D6:B0
           inet addr:172.20.1.31  Bcast:172.20.1.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:640 errors:0 dropped:0 overruns:0 frame:0
           TX packets:118 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:94134 (91.9 Kb)  TX bytes:9336 (9.1 Kb)
           Interrupt:11 Base address:0xdc00 Memory:dd021000-dd021038

[root at AL sbin]# ./ip addr show
1: lo: <LOOPBACK> mtu 16436 qdisc noqueue
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
     inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100
     link/ether 00:01:29:4c:06:46 brd ff:ff:ff:ff:ff:ff
     inet 172.20.1.30/24 brd 172.20.1.255 scope global eth0
3: eth1: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100
     link/ether 00:02:b3:a3:d6:b0 brd ff:ff:ff:ff:ff:ff
     inet 172.20.1.31/24 brd 172.20.1.255 scope global eth1
[root at AL sbin]# ./ip route show
172.20.1.0/24 dev eth0  scope link
172.20.1.0/24 dev eth1  proto kernel  scope link  src 172.20.1.31
169.254.0.0/16 dev eth1  scope link
default via 172.20.1.254 dev eth0
default via 172.20.1.254 dev eth1
[root at AL sbin]# ./route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use 
Iface
172.20.1.0      0.0.0.0         255.255.255.0   U     0      0        0 eth0
172.20.1.0      0.0.0.0         255.255.255.0   U     0      0        0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth1
0.0.0.0         172.20.1.254    0.0.0.0         UG    0      0        0 eth0
0.0.0.0         172.20.1.254    0.0.0.0         UG    0      0        0 eth1
[root at AL sbin]#



----------- my setups------------------------------------------------


_________eth0 172.20.1.30   _______________
|#1 PC  |-----------------> |Wireless AP  |
|Linux  |                   |Router       |->ADSL->Internet
|Http   |eth1 172.20.1.31   |172.20.1.254 |
|Server |...wireless......> |_____________|
|_______|                        ^
                                  |
__________                       |
|#2 PC   |                       |
|Windows |NIC 172.20.1.32        |
|Http    |-----------------------|
|client  |
|________|
 

Network: 172.20.1.X, netmask: 255.255.255.0
 

Ping test:
<on #2 PC> c:\ping 172.20.1.31
receive ping reply from #1 PC as long as eth0 is plug
even if wireless path not working.
If eth0 is unplug, c:\ping 172.20.1.31 won't get reply.
Thus, I think all traffic go to eth0 for linux if two
interfaces exist in the same subnetwork.
 

<if change #1 PC from Linux to Windows>
<on #2 PC> c:\ping 172.20.1.31, unplug eth0's wire won't affect
ping. That is, I think for windows:
ping 172.20.1.30 get reply from eth0, unplug eth1 won't affect ping
ping 172.20.1.31 get reply from eth1, upllug eth0 won't affect ping
 

 

 

My application:
#2 PC's browser can access #1 PC by IP address. I need
to ensure that when #2 PC access http://172.20.1.31,
traffic go thru eth1, not eth0. Can this be done in linux?
Or some commands (route/netmask/etc. settings)?
Or need change linux's IP stack source code a bit?


Thanks,

AL