Establishing Connection to Ethernet Switch

Question

I am trying to configure a basic network for a LAN. The LAN consist of only devices and an Ethernet switch. The devices are using Ubuntu.

To configure a basic network, the computers must be on the same subnet as the Ethernet port. In addition, the computer needs to use the same address of VLAN1 as the default gateway.

The Ethernet switch contains the IP interface VLAN1 with the address = 192.168.0.1 and the subnet = 255.255.255.0. The instructions I follow are in this configuration manual starting on page 35 - https://cache.industry.siemens.com/dl/files/218/109737218/att_1028764/v1/C79000-G8976-1280_ROS_v4.3_RS900W_ConfigurationManual.pdf. I will now explain my thought process.

The name of the Ethernet interface on my computer is eno1. I do the following:

In Ubuntu, I go to the Network settings and add a new wired connection. I set the name to eno1, set the MAC address with the drop down bar, then go to the IPv4 tab. I set the IPv4 Method to manual, set the address to 192.168.0.15, netmask to 255.255.255.0, and the gateway to 192.168.0.1.

I run the command netstat -r -n and I see that the eno1 interface has the destination 0.0.0.0 and a gateway of 192.168.0.1. How should I go about troubleshooting this issue?

I expect a wired connection to be established because I set the computer to be on the same subnet as the port and the default gateway to be that same as VLAN1. However, no connection is established and there is a question mark on the wired connection icon in Ubuntu.

Answer 1

The question mark in the Ethernet icon indicates that there is no Internet connectivity.

You say that there are only four computers connected to the switch. Unless there is some sort of router with an Internet connection also connected to the switch, you aren't going to have Internet access. This is ok, as long as you only want the computers to communicate amongst themselves. If you give the other computers addresses on the same subnet, you should even be able to ping them with your network configured as is.

The only real issue that I see is that you have your default gateway set to the VLAN address. I'm not familiar with Seimens equipment, but I believe that that is only a management address, meaning that you can connect to that address via HTTPS or SSH and configure the switch remotely. You shouldn't be forwarding traffic meant for other networks to that address.

The only situation where you would want to forward your traffic there is if you had a Layer 3 switch setup and you had other VLANs with which you wanted to communicate. Otherwise, you should set the default gateway to your router's address, if you have one.

By the way, destination 0.0.0.0 is a catch all, it means to forward all traffic to any unknown address to the default gateway. That is as it should be.

Answer 2

It is unclear to me what is happening here (not your fault, the term VLAN1 could be putting me off).

The first step I would attempt is to ping 192.168.0.1 from 192.168.0.15 and see if that works. If it works it means the computer can see the router, and you need to look if there is a default route.

If the ping does not work, I would look in the ARP table (arp -an on Linux and I think the same on windows) and see what entries are in the arp table. I would also try plug another computer into the lan and try and ping that and check the arp table.

Another thing to look at if ping does not work is if the interface is up on the switch and on the computer.