Routers have many of the same hardware and software components found in other computers, such as: CPU RAM ROM Operating System
Routers connect multiple networks, meaning it has interfaces that belong to different IP networks. Each network that a router connects to usually requires a separate interface: LAN (Ethernet) and WAN (Wide-Area or ISP).
Make sure you know these different router components – you WILL be asked about these components on the test!
Make sure to know the bootup processes – you WILL see this on the test! See pgs. 11 – 14 in your text for detailed information about each phase in the bootup process.
See pgs. 15 – 17 in your text for detailed information about the output of the show version command.
Main purpose of a router is to connect multiple networks and forward packets destined for its own networks or other networks. Routers are considered Layer 3 devices because its primary forwarding decision is based on the destination IP address of a packet. When a router receives a packet, it examines the destination IP address. If the destination IP address does not match any of the router’s directly connected networks, the router must then forward the packet to another router (or drop the packet if no match if found).
Remember, source and destination IP address DO NOT CHANGE as packets are transported from router to router. The MAC address WILL CHANGE at each router hop, because the router decapsulates the packet, examines the contents, and then re-encapsulates the packet with its MAC address to send to the next router.
Will demonstrate this on a real router in class and will have you do labs over this objective. Make sure you reference pgs. 25 – 29 in the text for detailed descriptions and examples over each configuration.
The running-config file is stored in RAM and is the file used by the IOS. Contents are lost when power is removed, unless it’s saved. The startup-config file is stored in NVRAM. Contents are not lost when power goes out. The show ip route command shows the routing table that the IOS is using to choose the best path to its destination networks. ALL show commands are executed from Privileged Exec Mode.
A directly connected network is a network that’s directly attached to one of the router interfaces. A remote network is a network that’s not directly connected to the router. Dynamic routes are routes to remote networks that were learned automatically by the router’s routing protocol. Static routes are routes that a network administrator manually configures.
See pgs. 44 – 45 in the text for full descriptions on each of the above mentioned IP packet fields.
Layer 2 Data-Link frame contains the header information with a source and destination MAC address, trailer information and the actual transmitted data. The Data-Link source address is the Layer 2 address of the interface that sent the Data-Link frame. As a packet is forwarded from router to router, the Layer 3 source and destination addresses WILL NOT CHANGE; however, the Layer 2 source and destination Data-Link addresses WILL CHANGE.
Important slide – will see this on test!
Important slide – will see this on test!
I think we’ve covered this concept before, as you can tell from the numerous repetitions, this concept is VERY important!
Introduction to Routing and Packet Forwarding Routing Protocols and Concepts – Chapter 1
-Computers that specialize in sending packets over the data network. They are responsible for interconnecting networks by selecting the best path for a packet to travel and forwarding packets to their destination
Routers determine a packets path to its destination by doing the following
Receiving an encapsulated frame & examining destination MAC address.
If the MAC address matches then Frame is de-encapsulated so that router can examine the destination IP address.
If destination IP address is in routing table or there is a static route then Router determines next hop IP address. Router will re-encapsulate packet with appropriate layer 2 frame and send it out to next destination.
Process continues until packet reaches destination.
Note - only the MAC addresses will change the source and destination IP addresses do not change.