L6 Network Layer 1 Flashcards
What are the two key functions of the network layer?
• Forwarding: Move packets from input link to output link at a router.
• Routing: Determine the path that packets take from source to destination.
What is the difference between the control plane and the data plane in the network layer?
• Control plane: Determines end-to-end paths through the network (routing algorithms).
• Data plane: Per-router operations that move packets from input to output ports.
In the network layer, what happens on the sending side?
• Segments are taken from the transport layer.
• Each segment is encapsulated into a datagram.
• Datagrams are sent to a nearby router.
What is the role of the network layer on the receiving side?
• Receives datagrams from the router.
• Extracts transport layer segments.
• Delivers segments to the transport layer.
Define Forwarding.
Router-local action transferring a packet from an input link to the correct output link.
Define Routing.
Network-wide action determining the end-to-end paths for packets.
How is a packet forwarded within a router?
• The router examines packet header fields.
• Uses header values to index into the forwarding table.
• Forwards the packet to the output interface indicated.
What is the traditional approach for configuring a router’s forwarding table?
• Routing algorithms run on each router.
• Routers exchange routing messages and compute their own forwarding tables.
How does the SDN (Software Defined Networking) approach differ?
• Routing is centralized in a remote controller.
• Controller computes and distributes forwarding tables to routers.
• Routers only perform forwarding.
List the four components of a router.
• Input ports
• Switching fabric
• Output ports
• Routing processor
What functions are performed by an input port in a router?
• Terminate incoming physical link.
• Perform link-layer functions.
• Lookup and determine output port.
• Forward control packets to routing processor.
What is the role of a routing processor in traditional routers?
• Execute routing protocols.
• Maintain routing tables and link-state information.
• Compute the forwarding table.
What is the goal of a routing algorithm?
Determine good paths (least cost, fastest, least congested) from sender to receiver.
What is the cost of a path in a network graph?
Sum of the costs of all individual links along the path.
Name types of routing algorithms based on network knowledge.
• Centralized: Each router has complete network information.
• Decentralized: Each router knows only its neighbors.
What is the difference between static and dynamic routing?
• Static: Routes change slowly over time.
• Dynamic: Routes update frequently with changes in network traffic or topology.
(Diagram 1) What does the first diagram represent overall?
The layered architecture (Application, Transport, Network, Data Link, Physical) across different devices and network components.
(Diagram 1) In the diagram, which layers are present at routers?
Network, Data Link, and Physical layers.
(Diagram 1) Which devices in the diagram implement the Application and Transport layers?
End hosts (laptops, servers, smartphones) implement the Application and Transport layers.
(Diagram 1) What is missing from the routers compared to end hosts in the diagram?
Routers do not implement Application or Transport layers.
(Diagram 1) How is communication established between end systems according to the layer model shown?
End systems use all layers; routers forward based on the Network layer information.
(Diagram 1) What role does the data link layer play at routers in the diagram?
Ensures correct data transfer between neighboring routers or devices.
(Diagram 1) Which layer ensures the physical transmission of bits?
The Physical layer.
(Diagram 2) What does the second diagram illustrate?
It shows how a router uses the local forwarding table to forward packets based on header values.
