Communication with a simple echo server works with RPi but not desktop Ubuntu

hamsterpoop · 10-01-2020, 07:36 AM

Hi guys.

I have been stuck on this problem for quite a while now and I humbly ask for your advice.

OS: Ubuntu 18.04.1
HW: Dell Precision 5820

I have a simple example ethernet echo server running on a FPGA evaluation board. The problem is that I am not able to communicate with it from my desktop running Ubuntu 18.04.1. I am, however, able to communicate with it from my Raspberry Pi.

The echo server aquires, without DHCP, an IP of 192.168.1.10, when connecting my RPi directly to the evaluation board I can type
"ping 192.168.1.10" and I observe packets sent back and forth on Wireshark.

My desktop has 2 ethernet interfaces, en0 and enp2s0. en0 is connected to the internet. When I simply type
"ping 192.168.1.10" the OS uses the en0 interface and we get, obviously, no response. I tried updating the ip route table by doing:
"sudo ip route add 192.168.1.10 dev enp2s0" but this had no effect.

What did have an effect was specifing what interface to use with ping:
"ping -I enp2s0 192.168.1.10" makes the ping requests go over the enp2s0 interface, But still there is no response. Inspecting the packet trace in Wireshark on both desktop and RPi reveals nothing. The message exchange seems identical except that the RPi gets a response and the desktop doesnt.

Any ideas for how to debug this further? This is, unfortunately, only one of many issues I am having with Ubuntu 18.04.1 which lends to the question if I should just wipe the computer and try Ubuntu 18.04.4 or maybe 20.04?

Thanks for your help

michaelk · 10-01-2020, 09:14 AM

Is your enp2s0 interface configured? Does it have an IP address?

Post the output of the command

Code:

ip addr show dev enp0s0

hamsterpoop · 10-01-2020, 09:25 AM

Hi Michael and thanks for your time!

I have not done anything to configure that interface. It doesnt have an IP address:

"ip addr show dev enp2s0
2: enp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
link/ether b4:96:91:8c:89:9e brd ff:ff:ff:ff:ff:ff
"

The ping's sent over the enp2s0 interface does report a source IP address that matches the en0 interface which is connect to the internet. Should I try to assign a static IP address to enp2s0? How does one do this?

michaelk · 10-01-2020, 10:11 AM

Normally, you would not use the same subnet on both interfaces.

ip addr add enp2s0 192.168.1.xxx dev ennp2s0 (xxx should be an unused IP address in that subnet 1 - 254 but not 10)

ip link set enp2s0 up

hamsterpoop · 10-02-2020, 03:33 AM

Thanks alot for your help Michael.

I was unable to configure the interface by using

Code:

ip addr add eno2s0 192.168.1.7 dev enp2s0

But I could configure a static IP address using the network gui in Ubuntu. Now I am able to communicate with the echo server. A curios observation is that I tried connecting the devices through a router, which should do DHCP, but still the enp2s0 didnt get an IP address.

Have a nice day and a great weekend