This module is a part of a larger series of networking labs using GNS3 in Proxmox. Click here to be taken back to the first pages in the series.

Proxmox: GNS3 Remote Server

In this post, I demonstrate how to get GNS3 Remote Server running in Proxmox, and how to connect to it using a GNS3 client on Windows.

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Previous Lab

Proxmox: GNS3 Lab 1

This is the first post in a computer networking mini-series following the University of the Pacific COMP 177 labs, using GNS3 hosted on my Proxmox server. In this post, we set up a very rudimentary network to test GNS3’s functionality.

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Reference Material

I'll be following along with this series of labs published by University of the Pacific for their COMP 177 class. The labs were originally published in 2020, but still offer some very valuable educational material.

Lab 2 - Intro to RouterOS | Pacific Cybersecurity

Pacific CybersecurityUniversity of the Pacific

The instructors have also provided us a brief introduction to working with MikroTik's RouterOS.

MikroTik RouterOS | Pacific Cybersecurity

Pacific CybersecurityUniversity of the Pacific

The Network Topology

Based on the lab documentation, we should have:

• Two VPCs
• One MikroTik Router
• One switch

Completing the Project

Create a New Project in GNS3

Building out the Network

Click the + button and reveal the node options. I've highlighted the node types we'll need to add to the work area in red.

Drag and drop each item onto the canvas to add it to the network environment. You can see that my environment matches the network diagram above. However, I have not yet added any links between the hosts.

Linking the Nodes

Just a brief detour to look at the MikroTik device... If you right-click the device and choose Show node information, you can see that the router ships with two ports.

Use the Add a link button to wire up the devices in your lab.

Link PC1:Ethernet0 to MikroTik:ether1.

Link MikroTik:ether2 to Switch1:Ethernet0.

Link Switch1:Ethernet1 to PC2:Ethernet0.

Final result.

Starting and Configuring the Nodes

We'll press the Start button to start all of the nodes at once.

Next, right-click each node and choose Web console. The switch does not have a console, as it is not a managed switch.

Configure MikroTik

Login with the username admin and a blank password. Choose n when prompted to view the license. You should be prompted to change the admin password.

Press CTRL + X to enter safe mode (as advised in the lab documentation).

Next, we will run two commands to configure the interfaces with IP addresses. You'll recall this router has two interfaces:

• ether1 — which is connected to PC1
• And, ether2 — which is connected to the switch

Configure Ether1

ip address add address=172.16.10.254/24 interface=ether1

• ether1 is the default gateway for PC1 for any communications where PC1 needs to reach another network
• We're giving ether1 the following configuration:
  • IP Address: 172.16.10.254
  • Subnet Mask: 255.255.255.0

Configure Ether2

ip address add address=172.16.20.254/24 interface=ether2

• ether2 is the default gateway for any host plugged into Switch1.
• Switch1 is currently just a dumb switch that extends the physical Ethernet medium for the Local Area Network (LAN) of 172.16.20.0/24.
• We're giving ether2 the following configuration:
  • IP Address: 172.16.20.254
  • Subnet Mask: 255.255.255.0

Give the Router a Hostname

system identity set name=gns3-mikrotik

Configure PC1

ip 172.16.10.1/24 172.16.10.254

We are giving PC1 the following configuration:

• IP Address: 172.16.10.1
• Subnet Mask: 255.255.255.0
• Default Gateway: 172.16.10.254

Configure PC2

ip 172.16.20.1/24 172.16.20.254

We are giving PC2 the following configuration:

• IP Address: 172.16.20.1
• Subnet Mask: 255.255.255.0
• Default Gateway: 172.16.20.254

Testing Connectivity

You can refer here for a more comprehensive overview of how data travels between two computers, as that's a bit out of scope of this article.

Computer Networking Flowchart

In this post, I will go over a simple diagram and show a couple scenarios on the way data travels between two hosts

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Inspecting Routing Tables

MikroTik

ip route print

Looking at MikroTik's routing table, you should be able to understand why it will be able to move packets between the PC1 and PC2.

Route 172.16.10.0/24

• MikroTik's routing table has 172.16.10.0/24 by way of 172.16.10.254 on ether1 interface
  • So if PC1 is at 172.16.10.1 and sends a packet to 172.16.20.1, this goes to the default gateway (MikroTik) at 172.16.10.254 for routing
  • MikroTik sees that 172.16.20.0/24 is on ether2, checks its ARP table for PC2's MAC address, and puts the packet on the wire to its destination

Route 172.16.20.0/24

• MikroTik's routing table has 172.16.20.0/24 by way of 172.16.20.254 on ether2 interface
  • Likewise if PC2 is at 172.16.20.1 and sends a packet to 172.16.10.1, this goes to its default gateway, 172.16.20.254 for routing
  • MikroTik sees that 172.16.10.0/24 is on ether1, checks its ARP table for PC1's MAC address, and puts the packet on the wire to its destination

PC1 to Default Gateway

PC1 is pinging the MikroTik ether1 interface, which should have no trouble, as they're both physically linked, and are configured statically with the same network address and subnet mask.

PC2 to Default Gateway

PC2 is pinging the MikroTik ether2 interface. This goes to Switch1, which looks at its CAM table to find the port where the MAC address of MikroTik's ether1 interface is plugged in. Switch1 then forwards the Ethernet frame onto MikroTik.

MikroTik replies, and the process repeats itself in reverse.

PC1 to PC2

PC1 is pinging a target on a foreign network. It sends the packet to the MikroTik router to complete its destination. The path of the packet is effectively:

PC2 to PC1

Since we covered the process more in-depth when looking at PC1, I'll summarize the packet path briefly here.

PC2 is pinging a target on a foreign network. It sends the packet to Switch1 — stamped with MikroTik's MAC address — and the switch sends the Ethernet frame to MikroTik. MikroTik routes the packet to its destination.

PC1 responds and the packet goes back to MikroTik, then to Switch1, and then onto PC2.

Up Next: GNS3 Lab 3

The lab 3 blog post is in the works and I'll link to it here as soon as I've finished it. Stay tuned.