Ethernet Queries on imx8mplus

[ssuresh]

Hi NXP Team,

[DESCRIPTION]
Please find the below 2 scenarios on ethernet.
In ifconfig we have 2 ethernet interfaces eth0 and eth1

Scenario 1:
Board ON
Connect the LAN cable between linux PC and eth0 port on board

Set the IP of eth0 (ifconfig eth0 192.168.1.250 up)
ping 192.168.1.250 ---> SUCCESS

Set the IP of eth1 (ifconfig eth1 192.168.1.251 up)
ping 192.168.1.251 ---> SUCCESS (Is this expected??)

Remove the LAN cable and connect between PC and eth1 port
ping 192.168.1.251 ---> NOT SUCCESS (Is this expected??)
ping 192.168.1.250 ---> NOT SUCCESS

Scenario 2:
Board ON
Connect the LAN cable between linux PC and eth0 port on board

Set the IP of eth1 (ifconfig eth1 192.168.1.17 up)
ping 192.168.1.17 ---> NOT SUCCESS

Set the IP of eth0 (ifconfig eth0 192.168.1.18 up)
ping 192.168.1.18 ---> NOT SUCCESS (Is this expected??)

Remove the LAN cable and connect between PC and eth1 port
ping 192.168.1.17 ---> SUCCESS
ping 192.168.1.18 ---> SUCCESS (Is this expected??)

Conclusion ---> to which interface we set the IP first, we can only use that port for packet transaction and also we observe a sharing of IPs between the eth0 and eth1 for the active port.

Is this behaviour expected? If yes, please let us know the reason.

[ssuresh]

Hi NXP Expert,

Yes this scenario is seen in i.MX 8M Plus EVK.

[JosephAtNXP]

Hi,

I could replicate,

I think that this issue and the other one is how is routed the packet and my assumption is based on this output.

Regards,

[JosephAtNXP]

Hi,

I conducted an experiment and showed that it's expected due to routes applied to the network section of the board, please feel free to try:

# Booted board shows no routes
$ ip route show table main

# Connect ETH0 to modem, as the IF is up, dhcp is assigned and shows routes
$ ip route show table main

# Assign an static IP to ETH1, increases a route (which is that the host routes ETH1 IP through ETH0)
$ ip route show table main

# Change cable to ETH1, the routes are limited and not swapped, shows that there needs to be an update for the routes or the workaround you have described
$ ip route show table main

Regards

[JosephAtNXP]

Hi,

Thank you for your interest in NXP Semiconductor products,

Can you replicate this on i.MX 8M Plus EVK?

Regards