Networking Concepts and Subnetting Quiz

Network Layer: Data Plane

• The network layer has two planes:
  • Data plane: local, per-router function. Determines how a datagram arriving at a router input port is forwarded to the router output port.
  • Control plane: network-wide logic. Determines how a datagram is routed among routers along an end-to-end path.

What's Inside a Router

• Input ports, switching, and output ports

Internet Protocol (IP)

• The Internet Protocol.
  • Datagram format: specific format for IP packets, including version number, header length, type of service, time to live (TTL), upper layer protocol, source IP address, destination IP address, options (if any), and payload data.
  • Addressing: 32-bit identifiers for hosts and routers, allowing for the identification of different devices.
  • Network address translation (NAT): allows multiple devices in a local network to share a single IP address with the outside world.
  • IPv6: a newer version of the Internet Protocol with 128-bit addresses, designed to address the limitations of IPv4.

Network Layer Functions

• Forwarding: the router-local action of moving packets from an input link to the appropriate output link.
• Routing: the network-wide process that determines the route taken by packets from source to destination. Includes routing algorithms.

Router Architecture Overview

• High-level view of generic router architecture. Routing processor, high-speed switching fabric, input ports, and output ports.

Input Port Functions

• Physical layer: bit-level reception (e.g., Ethernet, chapter 6).
• Link layer protocol (receive): lookup, forwarding, and queueing.
• Decentralized switching: using header field values for lookup and output port. Using forwarding table in the input port memory ("match plus action"). Destination-based forwarding (traditional) using destination IP address. Generalized forwarding using any header field value to forward packets based on a combination of values.

Destination-Based Forwarding

• A forwarding table to forward packets.

Longest Prefix Matching

• Use longest address prefix that matches the destination address to choose the appropriate entry in the forwarding table.

Switching Fabrics

• Transfer packets from input link to appropriate output link. Switching rate (measured as a multiple of input/output line rate). N inputs: switching rate N times line rate desirable.

Input Port Queuing

• Queuing may occur if the switch fabric is slower than the combined input ports. Queueing delay and loss may occur due to input buffer overflow.

Output Port Queuing

• Buffering required when datagrams arrive faster than link transmission rate. This can cause queuing (delay) and loss due to output buffer overflow. Scheduling discipline chooses among queued datagrams for transmission.

Network Layer: Internet Functions

• Path selection algorithm(implemented in routing protocols, e.g., OSPF, BGP, and SDN controller)

IP Datagram Format

• IP Protocol version number
• Header length in bytes
• Type of service (e.g., real-time, non-real time)
• Time-to-live (TTL)
• Upper layer protocol (e.g., TCP, UDP)
• Overhead (bytes of TCP, IP, application layer for TCP or UDP segment)
• Maximum length
• Checksums
• Source IP address
• Destination IP address
• Options (if any)
• Payload data (variable length, typically a TCP or UDP segment).

IP Addressing: Introduction

• IP address: 32-bit numerical identifier associated with each host or router interface.
• Interface: the connection between a host/router and a physical network link. Routers typically have multiple interfaces. Hosts typically have one or two like wired Ethernet or wireless 802.11

Subnets

• A subnet is a logical grouping of devices on a network that share the same subnet part of their IP addresses. Subnets are isolated from other subnets.
• IP Addresses have a structure: with the subnet part specifying (high order) common high order bits (for the same subnet), and the host part representing the lower order bits (remaining) in the IP address.
• Subnet mask: the format to specify the subnet part (high order).
• Subnets are defined by detaching interfaces from a host or router, and creating "islands" of isolated networks.

IP Addressing: CIDR

• CIDR: Classless InterDomain Routing (pronounced "cider"). The subnet portion of an address has an arbitrary length.
• Address format: a.b.c.d/x, where x is the number of bits in the subnet portion of the address.

IP Addresses: How to Get One?

• ICANN (Internet Corporation for Assigned Names and Numbers) allocates IP addresses through 5 regional registries (RRs)

Hierarchical Addressing: Route Aggregation

• Hierarchical addressing allows efficient advertisement of routing information.

Hierarchical Addressing: More Specific Routes

• When an organization moves from one ISP to another, the new ISP usually advertises a more specific route to the organization.

IP Addressing: Last Words

• ICANN allocates IP addresses through 5 regional registries.
• NAT (Network Address Translation) helps to conserve IPv4 addresses.
• IPv6 has a larger address space (128 bits).

NAT: Network Address Translation

• NAT allows multiple devices in a local network to share a single IP address with the outside world.

NAT: Implementation

• Replace source IP address and port numbers in outgoing datagrams with NAT's IP address and a new port number.
• For incoming datagrams, replace NAT's IP address and port numbers with the corresponding source IP address and port number.
• NAT router maintains a NAT translation table to keep track of these changes and map them.

IPv6: Motivation

• IPv6 was created because the 32-bit IPv4 address space was getting fully allocated. IPv6 provides a larger address space (128 bits instead of 32 bits)
• IPv6 includes expanded addressing capabilities and speed processing. Improves processing/forwarding with a 40-byte fixed length header. Enabling better quality of service or real-time service.

IPv6 Datagram Format

• Contains a priority field to sort datagrams in a flow
• Uses a flow label to identify datagrams in the same flow.
• Uses a 128-bit address
• Eliminates checksum to speed processing at routers
• No fragmentation or re-assembly
• No options provided (to be implemented in a higher layer protocol).

Transition from IPv4 to IPv6

• Tunneling: encapsulating IPv6 datagrams inside IPv4 datagrams to allow them to pass through IPv4 routers. This is often used when IPv6 routers are not present but IPv4 routers are used to connect two IPv6 networks.

Tunneling and Encapsulation

• Process of using an IPv4 network to tunnel IPv6 packets between two IPv6 networks.

IPv6 Adoption

• Significant adoption and deployment in network services.
• Long-term transition to IPv6 is underway and necessary.

Test your knowledge on fundamental networking concepts including forwarding, routing, and the components of the network layer. This quiz covers essential topics such as subnets, IP addresses, and the roles of devices like routers and switches in a network. Deepen your understanding of how these elements interact within a network environment.