TCP/IP Network Layer

Network Layer Fundamentals

• The primary responsibility of the network layer is host-to-host delivery of datagrams.
• The network layer delivers datagrams from the source host to the destination host.

Packet Delivery and Routing

• At the source host, a packet is encapsulated in a datagram and delivered to the data-link layer.
• The network layer at the destination host decapsulates the datagram, extracts the packet, and delivers it to the transport layer.
• A router delivers packets from one network to another network.
• Packetizing is the process of encapsulating the payload in a network-layer packet at the source and decapsulating it at the destination.

Error Control and Correction

• Error control means including a mechanism for detecting corrupted, lost, or duplicate datagrams.
• Error control is not implemented in the network layer because packets may be fragmented at each router, making error checking inefficient.
• ICMP is an auxiliary protocol that provides some form of error control if a datagram is discarded or has unknown information in the header.

Packet Switching and Circuit Switching

• Packet switching is more efficient in terms of resource utilization because it allows multiple packets to share the same link.
• The primary advantage of packet switching over circuit switching is its efficiency in terms of resource utilization.
• Packet switching is a connectionless service, whereas circuit switching is a connection-oriented service.

Router Functions

• Routers route packets based on the destination address contained in the packet header.
• Routers use forwarding tables to make forwarding decisions when a packet arrives at one of its interfaces.
• The primary function of a router is to route packets based on the destination address.

Connection-Oriented and Connectionless Services

• The datagram approach is connectionless, whereas the virtual circuit approach is connection-oriented.
• In the datagram approach, each packet is routed independently, whereas in the virtual circuit approach, a virtual connection is set up before sending packets.
• The flow label defines the virtual path the packet should follow in a connection-oriented packet-switched network.

Network Performance Metrics

• Latency is the total time taken for a complete message to arrive at the destination.
• Throughput is an actual measurement of how fast we can send data.
• High latency leads to the creation of bottlenecks in any network communication.
• Bandwidth is the potential measurement of a link, whereas throughput is the actual measurement of how fast we can send data.

Addressing and Subnetting

• The address space is the total number of addresses used by the protocol.
• Classful addressing became obsolete due to address depletion.
• Supernetting is used to combine several class C blocks into a larger block.
• Subnetting is used to divide a large block into smaller subnets, allowing for more efficient use of addresses.### Subnetting and Classless Addressing
• Supernetting involves combining several blocks into a larger block, allowing for more efficient use of addresses.
• In classless addressing, the prefix length is variable and can range from 0 to 32.
• The slash notation is used to indicate the prefix length in classless addressing.
• To find the first address in a block, you keep the n leftmost bits and set the (32 - n) rightmost bits all to 0s.
• The main difference between classful and classless addressing is that classful addressing uses fixed-length blocks, while classless addressing uses variable-length blocks.

Subnetting

• Subnetting involves dividing a range of addresses into several subranges and assigning each subrange to a subnetwork.
• The formula to find the prefix length for each subnetwork is nsub = 32 - log2Nsub.
• The size of the network is inversely proportional to the length of the prefix.
• The first step in designing subnets is to assign addresses to larger subnetworks.
• Subnetting is used to divide a network into smaller subnetworks.

Classless Addressing

• The main concept behind classless addressing is using variable-length blocks to divide the address space.
• The benefit of using classless addressing is that it provides more flexibility in assigning addresses.
• The formula to find the number of addresses in a block is N = 232 - n.
• The number of addresses in each subnetwork is inversely proportional to the prefix length.

DHCP

• DHCP simplifies the process of network configuration by automating the assignment of IP addresses, subnet masks, default gateways, DNS servers, and other settings.
• The DHCP server is a device on the network that is responsible for allocating and managing IP addresses and other configuration parameters.
• A DHCP client's lease has a duration, known as the lease time, after which the client must renew its lease.
• The DHCP Discover message is used to discover available DHCP servers on a network.
• The DHCP Request message is used to respond to a DHCP Offer message, indicating acceptance of the offered configuration.

NAT

• NAT (Network Address Translation) is a technology that allows a site to use private addresses for internal communication and global Internet addresses for communication with the rest of the world.
• Static NAT maps a private IP address to a specific public IP address.
• NAT provides the mapping between the private and universal addresses, and supports virtual private networks.

Routing

• Forwarding means delivering packets from the source to the destination without changing them.
• Routing involves delivering packets from the source to the destination without changing them.

Network Layer Fundamentals

• The primary responsibility of the network layer is host-to-host delivery of datagrams.
• The network layer delivers datagrams from the source host to the destination host.

Packet Delivery and Routing

• At the source host, a packet is encapsulated in a datagram and delivered to the data-link layer.
• The network layer at the destination host decapsulates the datagram, extracts the packet, and delivers it to the transport layer.
• A router delivers packets from one network to another network.
• Packetizing is the process of encapsulating the payload in a network-layer packet at the source and decapsulating it at the destination.

Error Control and Correction

• Error control means including a mechanism for detecting corrupted, lost, or duplicate datagrams.
• Error control is not implemented in the network layer because packets may be fragmented at each router, making error checking inefficient.
• ICMP is an auxiliary protocol that provides some form of error control if a datagram is discarded or has unknown information in the header.

Packet Switching and Circuit Switching

• Packet switching is more efficient in terms of resource utilization because it allows multiple packets to share the same link.
• The primary advantage of packet switching over circuit switching is its efficiency in terms of resource utilization.
• Packet switching is a connectionless service, whereas circuit switching is a connection-oriented service.

Router Functions

• Routers route packets based on the destination address contained in the packet header.
• Routers use forwarding tables to make forwarding decisions when a packet arrives at one of its interfaces.
• The primary function of a router is to route packets based on the destination address.

Connection-Oriented and Connectionless Services

• The datagram approach is connectionless, whereas the virtual circuit approach is connection-oriented.
• In the datagram approach, each packet is routed independently, whereas in the virtual circuit approach, a virtual connection is set up before sending packets.
• The flow label defines the virtual path the packet should follow in a connection-oriented packet-switched network.

Network Performance Metrics

• Latency is the total time taken for a complete message to arrive at the destination.
• Throughput is an actual measurement of how fast we can send data.
• High latency leads to the creation of bottlenecks in any network communication.
• Bandwidth is the potential measurement of a link, whereas throughput is the actual measurement of how fast we can send data.

Addressing and Subnetting

• The address space is the total number of addresses used by the protocol.
• Classful addressing became obsolete due to address depletion.
• Supernetting is used to combine several class C blocks into a larger block.
• Subnetting is used to divide a large block into smaller subnets, allowing for more efficient use of addresses.### Subnetting and Classless Addressing
• Supernetting involves combining several blocks into a larger block, allowing for more efficient use of addresses.
• In classless addressing, the prefix length is variable and can range from 0 to 32.
• The slash notation is used to indicate the prefix length in classless addressing.
• To find the first address in a block, you keep the n leftmost bits and set the (32 - n) rightmost bits all to 0s.
• The main difference between classful and classless addressing is that classful addressing uses fixed-length blocks, while classless addressing uses variable-length blocks.

Subnetting

• Subnetting involves dividing a range of addresses into several subranges and assigning each subrange to a subnetwork.
• The formula to find the prefix length for each subnetwork is nsub = 32 - log2Nsub.
• The size of the network is inversely proportional to the length of the prefix.
• The first step in designing subnets is to assign addresses to larger subnetworks.
• Subnetting is used to divide a network into smaller subnetworks.

Classless Addressing

• The main concept behind classless addressing is using variable-length blocks to divide the address space.
• The benefit of using classless addressing is that it provides more flexibility in assigning addresses.
• The formula to find the number of addresses in a block is N = 232 - n.
• The number of addresses in each subnetwork is inversely proportional to the prefix length.

DHCP

• DHCP simplifies the process of network configuration by automating the assignment of IP addresses, subnet masks, default gateways, DNS servers, and other settings.
• The DHCP server is a device on the network that is responsible for allocating and managing IP addresses and other configuration parameters.
• A DHCP client's lease has a duration, known as the lease time, after which the client must renew its lease.
• The DHCP Discover message is used to discover available DHCP servers on a network.
• The DHCP Request message is used to respond to a DHCP Offer message, indicating acceptance of the offered configuration.

NAT

• NAT (Network Address Translation) is a technology that allows a site to use private addresses for internal communication and global Internet addresses for communication with the rest of the world.
• Static NAT maps a private IP address to a specific public IP address.
• NAT provides the mapping between the private and universal addresses, and supports virtual private networks.

Routing

• Forwarding means delivering packets from the source to the destination without changing them.
• Routing involves delivering packets from the source to the destination without changing them.

Network Layer Services

• The network layer in the TCP/IP protocol suite is responsible for host-to-host delivery of datagrams.
• It provides services to the transport layer and receives services from the data-link layer.
• The network layer is involved at the source host, destination host, and all routers in the path.

Packetizing

• The first duty of the network layer is packetizing, which involves encapsulating the payload (data received from upper layer) in a network-layer packet at the source and decapsulating the payload from the network-layer packet at the destination.
• The network layer carries a payload from the source to the destination without changing it or using it.

Routing

• The network layer is responsible for routing the packet from its source to the destination.
• The network layer needs to have some specific strategies for defining the best route.
• Routing protocols are used to help routers coordinate their knowledge about the neighborhood and to come up with consistent tables to be used when a packet arrives.

Forwarding

• Forwarding is the action applied by each router when a packet arrives at one of its interfaces.
• The decision-making table a router normally uses for applying this action is sometimes called the forwarding table or routing table.
• When a router receives a packet from one of its attached networks, it needs to forward the packet to another attached network (in unicast routing) or to some attached networks (in multicast routing).

Error Control

• Error control means including a mechanism for detecting corrupted, lost, or duplicate datagrams.
• Error control also includes a mechanism for correcting errors after they have been detected.
• Although error control is not implemented in the network layer, the Internet uses an auxiliary protocol, ICMP, that provides some kind of error control.

Switching

• Switching is the passage of a message from a source to a destination and involves many decisions.
• There are two types of switching: circuit switching and packet switching.
• In circuit switching, a physical circuit is established between the source and destination of the message before the delivery of the message.
• In packet switching, the message is first divided into manageable packets at the source before being transmitted.

Network Layer Performance

• The performance of a network pertains to the measure of service quality of a network as perceived by the user.
• There are different ways to measure the performance of a network, depending upon the nature and design of the network.

Routing Efficiency: Latency (Delay)

• Latency (delay) is the total time taken for a complete message to arrive at the destination.
• Latency is affected by the source of the delays, including workstations, WAN links, routers, LAN, and servers.

Throughput

• Throughput is the number of messages successfully transmitted per unit time.
• Throughput is controlled by available bandwidth, the available signal-to-noise ratio, and hardware limitations.

Packet Loss

• Packet loss is another issue that severely affects the performance of communication.
• Packet loss occurs when a router receives a packet while processing another packet, and the received packet needs to be stored in the input buffer waiting for its turn.

IPv4 Address

• An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet.
• IPv4 addresses are unique and universal in the sense that each address defines one, and only one, connection to the Internet.

Classful Addressing

• Classful addressing is a system of dividing the address space into five classes: A, B, C, D, and E.
• Each class has a fixed prefix length and a fixed number of possible networks and hosts.

Address Depletion

• Address depletion is the reason that classful addressing has become obsolete.
• The classful addressing system has become obsolete due to the rapid growth of the Internet and the need for more addresses.

Subnetting and Supernetting

• Subnetting is the process of dividing a class A or class B block into several subnets.
• Supernetting is the process of combining several class C blocks into a larger block.

Classless Addressing

• Classless addressing is a system of dividing the address space into variable-length blocks.
• In classless addressing, the whole address space is divided into variable-length blocks, and the prefix in an address defines the block (network), and the suffix defines the node (device).### Classless Addressing
• Classful addressing is a special case of classless addressing, where variable-length blocks are used that belong to no classes.
• In classless addressing, the prefix length in an address defines the block (network), and the suffix defines the node (device).
• The size of the network is inversely proportional to the length of the prefix.

Prefix Length and Slash Notation

• The prefix length, n, is added to the address, separated by a slash (slash notation or CIDR strategy).
• The number of addresses in a block is found as N = 2^(32-n).
• To find the first address, keep the n leftmost bits and set the (32 - n) rightmost bits all to 0s.
• To find the last address, keep the n leftmost bits and set the (32 - n) rightmost bits all to 1s.

Subnetting

• An organization can divide a range of addresses into subranges and assign each subrange to a subnetwork (subnet).
• Subnetworks can be divided into sub-subnetworks, and so on.
• When designing subnets, the number of addresses in each subnet should be a power of 2.
• The prefix length for each subnet should be found using the formula: nsub = 32 - log2Nsub.

Dynamic Host Configuration Protocol (DHCP)

• DHCP is a network management protocol used to dynamically assign IP addresses and other network configuration parameters to devices on a network.
• DHCP operates on the client-server model, where a DHCP server manages and allocates IP addresses to DHCP clients.
• DHCP clients request and obtain network configuration information from a DHCP server.

DHCP Components

• DHCP server: manages and allocates IP addresses and other configuration parameters.
• DHCP client: requests and obtains network configuration information from a DHCP server.
• Lease: a temporary assignment of an IP address and other configuration parameters to a DHCP client.

DHCP Process

• DHCP Discover: a client broadcasts a message to discover available DHCP servers on the network.
• DHCP Offer: a DHCP server responds with an offered IP address and configuration parameters.
• DHCP Request: the client selects an offered IP address and sends a request message to the chosen DHCP server.
• DHCP Acknowledgment: the DHCP server confirms the assignment of the IP address and provides the client with the configuration parameters.

Network Address Translation (NAT)

• NAT provides a mapping between private and universal addresses, supporting virtual private networks.
• NAT types:
  • Static NAT: maps a private IP address to a specific public IP address.
  • Dynamic NAT: maps private IP addresses to public IP addresses from a pool of available addresses.
  • NAT Overload (PAT): maps multiple private IP addresses to a single public IP address using different source port numbers.

Forwarding of IP Packets

• Forwarding delivers a packet to the next hop (final destination or intermediate connecting device).
• IP can be used as a connectionless or connection-oriented protocol.
• Forwarding can be based on the destination address of the IP datagram or a label attached to an IP datagram.
• A forwarding table is used to find the next hop to deliver the packet to.