28 Dynamic Networking – Open Shortest Path First
Mathew J. Heath Van Horn, PhD and Jacob Christensen
Open Shortest Path First (OSPF) is quite complicated to implement, but it makes things very simple for users. Its essence is that routers share information with each other so that when a data packet needs to go from Point A to Point B, all the routers know the fastest path through the network. The “fastest path” can be decided by the physical distance between routers (speed of light energy loss), electrical distance (router hops), and availability and reliability. This means you can’t just look at a network diagram and make assumptions about speed. In this lab, we will build an OSPF network with several paths. We will look at how the OSPF builds a network topology and shares the information amongst the routers. We will also watch how the familiar ICMP packets traverse the network.
Estimated time for completion: 30 minutes
Learning objectives
- Successfully configure an enterprise network to use OSPF routing
- Use Wireshark to identify packets specifically associate with OSPF
- Implement a DHCP Relay solution to an enterprise network
- Use CIDR subnetting techniques to minimize the IP network space waste
Prerequisites
Deliverables
- 5 screenshots are required to receive full credit for this assignment
- GNS3 working environment will have all devices on and labeled correctly
- A router display of all the IP routes – all four router IDs should be visible
- Wireshark showing OSPF Hello Packets
- Wireshark shows ICMP packets between PC1 and PC3 using one path
- Wireshark shows ICMP packets between PC1 and PC3 using a different path
Resources
- MikroTik RouterOS Documentation – OSPF – https://help.mikrotik.com/docs/display/ROS/OSPF
- IBM – Packet Types for OSPF – https://www.ibm.com/docs/en/i/7.1?topic=concepts-packet-types-ospf
Contributors and Testers
- Dante Rocca, Cybersecurity Student, ERAU-Prescott
Phase I – Terminology
OSPF relies on many terms to describe the relationship between the routers and the routing processes. We will use many of these in this lab, so we will list them here. The list is from the MikroTik RouterOS manual but will be summarized. so you don’t have to flip back and forth between websites.
- Adjacency – A logical connection between a router and a designated router and a backup designated router. No routing information is exchanged unless adjacencies are formed.
- Area Border Router (ABR) – A router that is connected to multiple areas and is responsible for summarizing and update suppression between network areas.
- Autonomous System (AS) – Routers that use a common routing protocol to exchange information.
- Autonomous System Boundary Router (ASBR) – A term used to describe a router that is connected to an external network and imports the external routes into the OSPF topology.
- Back-up Designated Router (BDR) – A hot standby for the designated router and receives all routing updates from adjacent routers, but does not flood