Module 8: Network Layer

(4) Basic Network Layer Operations

(1) Addressing end devices (2) Encapsulation (3) Routing (4) De-encapsulation

What (3) sections related to the current TCP/IP network connections are displayed when the netstat -r or route print commands are inputted

(1) Interface List - lists MAC address and assigned interface number of every network-capable interface on the host (includig Ethernet, wifi, and bluetooth) (2) IPv4 Route Table - lists all know IPv4 routes including direct connections, local network, and local default routes (3) IPv6 Route Table - Lists all known IPv6 routes including direct connections, local network, and local default routes

What are the three destinations a computer communicates with?

(1) Itself (2) Local host (3) Remote host

(3) Basic Characteristics of IP

(1). Connectionless - there is no connection with the destination established before sending data packets (2) Best Effort - IP is inherently unreliable because packet delivery is not guaranteed (3) Media Independent - Operation is independent of the medium carrying the data

What are some impacts and limitations of Packet Fragmentation

- It causes latency - IPv6 packets cannot be fragmented by a router

What is the special self-ping address for IPv4?

127.0.0.1

(IPv6 header fields) - Destination IPv6 Address

128-bit field that identifies the IPv6 address of the receiving host

(IPv6 header fields) - Source IPv6 Address

128-bit field that identifies the IPv6 address of the sending host

(IPv6 header fields) - Payload Length

16-bit field indicates the length of the data portion or payload of the IPv6 packet. Does not include lenght of the IPv6 header (which is a fixed 40-byte header)

(IPv6 header fields) - Flow Label

20-bit field suggests that all packets with the same flow label receive the same type of handling by routers

(IPv6 header fields) - Traffic Class

8-bit field equivalent to the IPv4 Differentiated Services (DS) field.

(IPv6 header fields) - Next Header

8-bit field equivalent to the IPv4 Protocol field. Indicates the data payload type that the packet is carrying (enabling the network layer to pass the data to the appropriate upper-layer protocol)

(IPv6 header fields) - Hop Limit

8-bit field that replaces the IPv4 TTL. Decremented by 1 each time a new router forwards the packet. Packet is discarded when the counter reaches 0.

What is the special self-ping address for IPv6?

::1

(IPv4 header fields) - Version

Contains a 4-bit binary value set to 0100 that identifies this as an IPv4 packet.

(Basic Layer 3 Operations) - Addressing end devices

End devices must be configured with a unique IP address for identification on the network.

Describe Fragmentation of a Packet

Ex: In some cases, an intermediate device, usually a router, must split up an IPv4 packet when forwarding it from one medium to another with a smaller MTU. This process is called fragmenting the packet.

Describe (3) limitations of IPv4

IPv4 address depletion - limited number of unique public addresses available but IP-enabled devices are growing Lack of end-to-end connectivity - Network Address Translation (provides way for multiple addresses to share public IPv4 address) can be problematic for technologies requiring end-to-end connectivity Increased network complexity - added complexity from NAT leads to latency and increased difficulty in troubleshooting.

Describe (3) improvements brought by IPv6

Increased address space - IPv6 is based on a 128-bit hierarchical addressing vs the 32-bit IPv4 Improved packet handling - IPv6 header has been simplified with fewer cards Eliminates need for NAT - there are so many address available that NAT isn't necessary

What fields are used to identify and validate an IP packet

Internet Header Length (IHL), Total Length, and Header Checksum

Maximum Transmission Unit

MTU - the maximum size of the PDU that each medium can transport. Part of the control communication between the data link layer and the network layer is establishment of the max size for a packet.

OSI Layer 3 - Network Layer

OSI Layer that provides services to allow end devices to exchange data across networks

(Basic Layer 3 Operations) - Routing

The Network layer provides services to direct the packets to a destination host on another network. To travel to other networks, the packet must be processed by a router. The router's role is to choose the best path and direct packets toward the destination host. A packet may cross many routers before reaching the destination host. Each router a packet crosses to reach the destination is called a hop

(Basic Layer 3 Operations) - Encapsulation

The network layer process where the PDU from the transport layer in encased in a packet. The _______ process adds IP header information such as source and destination IP addresses of the hosts. The ________ process is performed by the source of the IP packet.

Describe what a routing table contains

The router examines the destination IP address of the packet and searches its routing table to determine where to forward the packet.

What happens when a packet arrives on a router interface?

The router examines the destination IP address of the packet and searches its routing table to determine where to forward the packet. The router will forward the packet using the best (longest) matching route entry.

(IPv4 header fields) - Time to Live

This contains an 8-bit binary value that is used to limit the lifetime of a packet. The source device of the IPv4 packet sets the initial ______ value. It is decreased by one each time the packet is processed by a router. If the _____ field decrements to zero, the router discards the packet and sends and Internet Control Message Protocol (ICMP) Time Exceeded message to the source IP address. Because the router decrements the ______ of eah packet, the router must also recalculate the Header Checksum.

(IPv4 header fields) - Header Checksum

This is used to detect corruption in the IPv4 header

(Basic Layer 3 Operations) - De-encapsulation

When the packet arrives at the network layer of the destination host, the host checks the IP header of the packet. If the destination IP matches it's own IP, the IP header is removed from the packet. After the packet is _________ by the network layer, the resulting Layer 4 PDU is passed up to the appropriate service at the transport layer. The ___________ process is performed by the destination host of the IP packet.

dynamic routing protocol

allows the routers to automatically learn about remote networks, including a default route, from other routers

route print

command used to display the host routing table for a Window host

netstat -r

command used to display the host routing table for a Windows host

(IPv6 header fields) - Version

contains 4-bit binary value set to 0110 that identifies this as an IPv6 packet

(IPv4 header fields) - Differentiated Services or DiffServ (DS)

formerly called the type of service (ToS) field, this field is and 8-bit field used to determine the priority of each packet. The xis ost significant bits of the ________field are teh differentiated services code point (DSCP) bits and the last two bits are the explicit congestion notification (ECN) bits

IPv6 extension header (EH)

optional network layer information placed between the IPv6 header and the payload. Used for things like fragmentation, security, to support mobility, etc.

Static route

route entries that are manually configured

(IPv4 header fields) - Destination IPv4 Address

this contains a 32-bit binary value representing the destination IPv4 address of the packet. It can be unicast, multicast, or a broadcast address.

(IPv4 header fields) - Source IPv4 Address

this contains a 32-bit binary value that represents the source IPv4 address of the packet. It is always a unicast address.

(IPv4 header fields) - Protocol

this field is used to identify the next level rules or "__________". This 8-bit binary value indicates he data payload type that the packet carries, which enables the network layer to pass the data to the appropriate upper-layer protocol. Common values include ICMP, TCP, and UDP