PROCESSOR-SDK-AM437X: AM437x ETH0 and ETH1 loopback - ping not working

Hello,

The subnet is the 3rd number in the IP address. so for eth0 = 192.168.1.100, the subnet is 1. Even if two ethernet ports are physically connected, they will only look for communication on their subnet. Since one ethernet port is on subnet 1 and the other ethernet port is on subnet 2, it makes sense that you cannot ping from one to another.

The constraint says, if your Ethernet ports are physically connected to each other (for example, both plugged into the same external Ethernet switch or the same network), they should be on different subnets. If you are curious about why that is required, let me know and I will find where we document the reasoning.

Off the top of my head, I am not sure what would happen if you are doing a loopback from one Ethernet port to the other. Try putting them on the same subnet (e.g., 192.168.1.100 and 192.168.1.101) and see what happens.

Regards,

Nick

Following up: Without testing, I cannot say for sure what would happen when doing loopback with Linux Ethernet ports. However, there is potential that 1) The loopback test would not work, or 2) The kernel would figure out the source and destination is the host machine, and then just pass the data between the two applications without sending anything out an Ethernet port. So my initial suggestion would be to test Ethernet with a separate link partner (PC, a second AM437x EVM, etc).

Regards,

Nick

Hello Nick,

I tried putting eth0 & eth1 on same subnet on our hardware and AM4378 SK EVM, but I am not able to see ping working on our hardware as well as on AM4378 SK EVM.

see the following log:

#Our hardware

root@picv6-1:~# ifconfig eth0; ifconfig eth1
eth0      Link encap:Ethernet  HWaddr 14:42:FC:D2:84:61
          inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: 2001:db8::1642:fcff:fed2:8461/128 Scope:Global
          inet6 addr: fe80::1642:fcff:fed2:8461/64 Scope:Link
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:86 errors:0 dropped:0 overruns:0 frame:0
          TX packets:54 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3000
          RX bytes:16451 (16.0 KiB)  TX bytes:9965 (9.7 KiB)
          Interrupt:48

eth1      Link encap:Ethernet  HWaddr 14:42:FC:D2:84:63
          inet addr:192.168.1.101  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::1642:fcff:fed2:8463/64 Scope:Link
          inet6 addr: 2001:db8::1642:fcff:fed2:8463/128 Scope:Global
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:52 errors:0 dropped:0 overruns:0 frame:0
          TX packets:86 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3000
          RX bytes:9873 (9.6 KiB)  TX bytes:16107 (15.7 KiB)

root@picv6-1:~# ping -I eth0 192.168.1.101
PING 192.168.1.101 (192.168.1.101) from 192.168.1.100 eth0: 56(84) bytes of data.
^C
--- 192.168.1.101 ping statistics ---
9 packets transmitted, 0 received, 100% packet loss, time 326ms
pipe 3
root@picv6-1:~# ping -I eth1 192.168.1.100
PING 192.168.1.100 (192.168.1.100) from 192.168.1.101 eth1: 56(84) bytes of data.
^C
--- 192.168.1.100 ping statistics ---
6 packets transmitted, 0 received, 100% packet loss, time 233ms
pipe 3
root@picv6-1:~#


#SK EVM
root@am437x-evm:~# ifconfig -a
eth0      Link encap:Ethernet  HWaddr C4:BE:84:CC:87:B2
          inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:20 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:6840 (6.6 KiB)
          Interrupt:72

eth1      Link encap:Ethernet  HWaddr C4:BE:84:CC:87:B4
          inet addr:192.168.1.101  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING 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)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:118 errors:0 dropped:0 overruns:0 frame:0
          TX packets:118 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:193518 (188.9 KiB)  TX bytes:193518 (188.9 KiB)

root@am437x-evm:~# ping -I eth0 192.168.1.101
PING 192.168.1.101 (192.168.1.101): 56 data bytes
^C
--- 192.168.1.101 ping statistics ---
9 packets transmitted, 0 packets received, 100% packet loss
root@am437x-evm:~# ping -I eth1 192.168.1.100
PING 192.168.1.100 (192.168.1.100): 56 data bytes
^V^C
--- 192.168.1.100 ping statistics ---
7 packets transmitted, 0 packets received, 100% packet loss
root@am437x-evm:~

1) The loopback test would not work

• On our previous hardware which is AM335x bases, we used to run board level functional testing by doing loopback with Linux Ethernet ports. We had no problem pinging from eth0 to eth1.

2) The kernel would figure out the source and destination is the host machine, and then just pass the data between the two applications without sending anything out an Ethernet port

• kernel will pass the data between two application if we do not provide "-I" option while pinging. When we provide -I option while pinging kernel sends data out on Ethernet port 

So my initial suggestion would be to test Ethernet with a separate link partner (PC, a second AM437x EVM, etc)

• I have tested ethernet with separate link partner and it works with PC