26 Static Networking Part 2

Up to this point, we have been using one router in our working environments that use DHCP. However, you will rarely work on a network with only one router because the whole point of an enterprise network is to connect multiple LANs into a single cohesive network.

In this lab, we will create and connect three LANs via three routers. We introduce you to static routing solutions so you can become familiar with routing procedures. Static routing is impractical mainly because it is very manpower intensive to maintain and prone to human error.

Estimated time for completion: 60 minutes

Learning objectives

• Successfully create three functional LANs:
  • Gray (DHCP Server)
  • Red (Switch + 2 PCs)
  • Blue (Switch + 2 PCs)
• Configure three routers to use static routing so all devices can communicate

Prerequisites

• Chapter 20 – Static Networking Part 1
• Chapter 21 – DHCP Relay

Deliverables

4 screenshots are required to receive credit for this lab

• Screenshot of GNS3 workspace with everything labeled
• Screenshot of the DHCP configuration
• Wireshark Screenshots of a Red host successfully pinging:
  • Blue Host
  • Gray Host

Resources

• MikroTik RouterOS Documentation – IP Routing – https://help.mikrotik.com/docs/display/ROS/IP+Routing

Contributors and Testers

• Dante Rocca, Cybersecurity Student, ERAU-Prescott

Phase I -Building the Topology

The following steps are to create the baseline for completing the lab.  It makes assumptions about learner knowledge from completing previous labs.  To reduce the amount of stress on the PC, we will be using Linux boxes for DHCP.

By the end of this chapter, your network should look like the following:

1. Open GNS3
   1. Create a new project: LAB_12
2. Build a small network with the following specifications:
   1. Class B Supernet – 10.0.0.0/16
      

      Host Range
      Host Lower Bound	10.0.0.1
      Host Upper Bound	10.0.255.254

      NOTE: Our supernet is the total IP address space we are allowed to use for this network. We will subnet this as necessary to fit our needs for each LAN. If you still confused how subnetting works, there are plenty of online tools that can help augment your learning!

   2. Subnet – Red
      1. One switch – Ethernet switch
      2. Two client machines – VPCS
      3. Minimize wasted address space for 300 hosts
         

         Network Information
         Network	10.0.0.0
         Netmask	255.255.254.0 (/23)
         Broadcast	10.0.1.255
         Gateway	10.0.0.1
         DHCP Lower Bound	10.0.0.100
         DHCP Upper Bound	10.0.1.250

         NOTE: I am choosing to reserve the first usable host for my gateway addresses. In addition, my DHCP range does not include every single host address available (mostly because I like clean numbers). These are not hard and fast rules. Feel free to adjust as necessary.

   3. Subnet – Blue
      1. One switch – Ethernet switch
      2. Two client machines – VPCS
      3. Minimize wasted address space for 150 hosts
         

         Network Information
         Network	10.0.2.0
         Netmask	255.255.255.0 (/24)
         Broadcast	10.0.2.255
         Gateway	10.0.2.1
         DHCP Lower Bound	10.0.2.100
         DHCP Upper Bound	10.0.2.250

   4. Subnet – Gray
      1. One DHCP server – Ubuntu 22.04.X LTS
         

         NOTE: In this example, the server will have a static IP address of 10.0.3.6.

      2. Minimize wasted address space for 6 hosts
         

         Network Information
         Network	10.0.3.0
         Netmask	255.255.255.248 (/29)
         Broadcast	10.0.3.7
         Gateway	10.0.3.1

   5. Subnet – Backbone
      1. Three routers – MikroTik CHR
      2. Full-mesh topology

         NOTE: The term full-mesh simply means that each node is connected to every other node.

      3. Minimize wasted address space for each router-to-router connection
         

         Connection	Network
         Router1 <-> Router2	10.0.4.0/30
         Router1 <-> Router3	10.0.5.0/30
         Router2 <-> Router3	10.0.6.0/30

3. Connect each LAN to their own router
4. Label and organize your network as necessary
   

   

1. Login to Router1 and open its console
   1. Set static IP addresses for all active network interfaces (Figure 3)
      

      Interface	Network	IPv4 Address
      ether1 -> Red	10.0.0.0/23	10.0.0.1
      ether2 -> Router2	10.0.4.0/30	10.0.4.1
      ether3 -> Router3	10.0.5.0/30	10.0.5.1

      NOTE: Refer to Chapter 16, Phase II for additional information on how to configure IP address in MikroTik.

   2. Configure Router1 to act as a relay for DHCP discover packets (Figure 4)

      > ip dhcp-relay add name=Red-Relay interface=ether1 dhcp-server=10.0.3.6 local-address=10.0.0.1 disabled=no

      NOTE: You only need to configure DHCP forwarders for networks directly connected to the relay. In this case, only the Red subnet is attached to this router, so only one relay needs to be made. Refer to Chapter 21, Phase II for additional information.

   3. Statically update Router1’s  routing table with routes to the Blue and Gray networks (Figure 5)

      NOTE: Two routes need to be created for every subnet, with each specifying the same destination via different gateways (Router2 and Router3). This is a form of redundancy that ensures network functionality even in the case of either path going offline. When building networks, it is important to mitigate as many single point of failures as possible to ensure availability and reliability.

      1. Add all routes to the Blue subnet

         > ip route add dst-address=10.0.2.0/24 gateway=10.0.4.2 distance=1

         > ip route add dst-address=10.0.2.0/24 gateway=10.0.5.2 distance=2

         NOTE: The distance option specifies how many additional routers are needed to reach the destination network. The route with the shortest number of hops will take priority over the other.

      2. Add all routes to the Gray subnet

         > ip route add dst-address=10.0.3.0/29 gateway=10.0.5.2 distance=1

         > ip route add dst-address=10.0.3.0/29 gateway=10.0.4.2 distance=2

2. Login to Router2 and open its console
   1. Set static IP addresses for all active network interface (Figure 6)
      

      Interfaces	Network	IPv4 Address
      ether1 -> Blue	10.0.2.0/24	10.0.2.1
      ether2 -> Router1	10.0.4.0/30	10.0.4.2
      ehter3 -> Router3	10.0.6.0/30	10.0.6.1

   2. Configure Router2 to act as a relay for DHCP discover packets (Figure 7)

      > ip dhcp-relay add name=Blue-Relay interface=ether1 dhcp-server=10.0.3.6 local-address=10.0.2.1 disabled=no

   3. Statically update Router2’s routing table with routes to the Red and Gray networks (Figure 8)
      1. Add all routes to the Red subnet

         > ip route add dst-address=10.0.0.0/23 gateway=10.0.4.1 distance=1

         > ip route add dst-address=10.0.0.0/23 gateway=10.0.6.2 distance=2

      2. Add all routes to the Gray subnet

         > ip route add dst-address=10.0.3.0/29 gateway=10.0.6.2 distance=1

         > ip route add dst-address=10.0.3.0/29 gateway=10.0.4.1 distance=2

3. Login to Router3 and open its console
   1. Set static IP addresses for all active network interfaces (Figure 9)
      

      Interfaces	Network	IPv4 Address
      ether1 -> Gray	10.0.3.0/29	10.0.3.1
      ether2 -> Router1	10.0.5.0/30	10.0.5.2
      ether3 -> Router2	10.0.6.0/30	10.0.6.2

      NOTE: We will not configure any DHCP relays on this device since there is no DHCP-dependent LAN that is directly connected to it. The Gray subnet will only consist of statically assigned host addresses.

   2. Statically update Router3’s  routing table with routes to the Red and Blue networks (Figure 10)
      1. Add all routes to the Red subnet

         > ip route add dst-address=10.0.0.0/23 gateway=10.0.5.1 distance=1

         > ip route add dst-address=10.0.0.0/23 gateway=10.0.6.1 distance=2

      2. Add all routes to the Blue subnet

         > ip route add dst-address=10.0.2.0/24 gateway=10.0.6.1 distance=1

         > ip route add dst-address=10.0.2.0/24 gateway=10.0.5.1 distance=2

4. Verify that all three routers can ping each other before continuing to the next section

1. Start the DHCP server and login
   1. Configure the network interface with the static IPv4 address 10.0.3.6 (Figure 11)
   2. Modify the DHCP daemon configuration file to support the Red and Blue networks (Figure 12)
2. Start PC1 and open its console
   1. Test the DHCP service by requesting a new IP address

      > ip dhcp

   2. Test the reliability of the network by cutting the Router1-Router3 link
      

      

   3. Request a new IP address

      > ip dhcp

3. Repeat step 2 with a client device from the Blue network

   NOTE: Try cutting the Router2-Router3 link instead. We are trying to see if the routers can successfully redirect packets via the longest path!

Congratulations! You were able to create small network with multiple routers by manually administering the routing tables. Hopefully by the end of this exercise you realize how tedious and error-prone this can be as network sizes increases. Luckily, the next few chapters will introduce new protocols that can automate this process for a much friendlier experience.

End of Lab

Figures for Printed Version