two netcard configed in one subnet problem

[hu jun]

two linux machines A and B , they are in one network: 192.168.160.0

A has two netcards:
eth0      Link encap:Ethernet  HWaddr 00:0C:29:F9:DD:29          inet addr:192.168.160.11  Bcast:192.168.160.255  Mask:255.255.255.0          inet6 addr: fe80::20c:29ff:fef9:dd29/64 Scope:Link          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1          RX packets:448 errors:0 dropped:0 overruns:0 frame:0          TX packets:361 errors:0 dropped:0 overruns:0 carrier:0          collisions:0 txqueuelen:1000          RX bytes:42722 (41.7 Kb)  TX bytes:46887 (45.7 Kb)
eth1      Link encap:Ethernet  HWaddr 00:0C:29:F9:DD:33          inet addr:192.168.160.21  Bcast:192.168.160.255  Mask:255.255.255.0          inet6 addr: fe80::20c:29ff:fef9:dd33/64 Scope:Link          UP BROADCAST MULTICAST  MTU:1500  Metric:1          RX packets:73 errors:0 dropped:0 overruns:0 frame:0          TX packets:7 errors:0 dropped:0 overruns:0 carrier:0          collisions:0 txqueuelen:1000          RX bytes:9926 (9.6 Kb)  TX bytes:578 (578.0 b)                    B has one netcard:
eth0      Link encap:Ethernet  HWaddr 00:0C:29:A9:5F:E2          inet addr:192.168.160.12  Bcast:192.168.160.255  Mask:255.255.255.0          inet6 addr: fe80::20c:29ff:fea9:5fe2/64 Scope:Link          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1          RX packets:793 errors:0 dropped:0 overruns:0 frame:0          TX packets:649 errors:0 dropped:0 overruns:0 carrier:0          collisions:0 txqueuelen:1000          RX bytes:74366 (72.6 Kb)  TX bytes:80645 (78.7 Kb)          Interrupt:17 Base address:0x2000          
now on B :ping 192.168.160.11 and 192.168.160.21, both are ok
run arp -a,result is as follows:? (192.168.160.21) at 00:0C:29:F9:DD:29 [ether] on eth0? (192.168.0.59) at 00:0C:29:F9:DD:1F [ether] on eth1? (192.168.160.1) at 00:50:56:C0:00:01 [ether] on eth0? (192.168.0.1) at 00:11:95:CD:35:66 [ether] on eth1Vsles11sp1 (192.168.160.11) at 00:0C:29:F9:DD:29 [ether] on eth0

then I unplug eth1 , ethtool eth1 show "Link detected: no",
now on B :ping 192.168.160.11 and 192.168.160.21, both are ok, too.
I was confused that things.
Google , I has understanded a little . 
on A , I run "echo 1 >/proc/sys/net/ipv4/conf/all/arp_ignore",then on B , ping ping 192.168.160.11 and 192.168.160.21, both still are ok
Can you give me advise ?
What will I do for on B pinging 192.168.160.21 is not ok?

          
 		 	   		  
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