Module 8: Network Layer Flashcards
Provides services to allow end devices to exchange data across networks
The network layer (OSI Layer 3)
Are the principle network layer communication protocols
IP version 4 (IPv4) and IP version 6 (IPv6)
Other network layer protocols
Open Shortest Path First (OSPF)
Messaging protocols such as Internet Control Message Protocol (ICMP).
To accomplish end-to-end communications across network boundaries, network layer protocols perform four basic operations:
Addressing end devices
Encapsulation
Routing
Decapsulation
Network Layer basic operation wherein End devices must be configured with a unique IP address for identification on the network.
Addressing end devices
Network Layer basic operation wherein the network layer encapsulates the protocol data unit (PDU) from the transport layer into a packet.
This process adds IP header information, such as the IP address of the source (sending) and destination (receiving) hosts. The encapsulation process is performed by the source of the IP packet.
Encapsulation
Network Layer basic operation wherein 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 role of the router is to select the best path and direct packets toward the destination host in a process known as routing. A packet may cross many routers before reaching the destination host. Each router a packet crosses to reach the destination host is called a hop.
Routing
Network Layer basic operation wherein 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 address within the header matches its own IP address, the IP header is removed from the packet.
After the packet has been _______ by the network layer, the resulting Layer 4 PDU is passed up to the appropriate service at the transport layer. This process is performed by the destination host of the IP packet.
De-encapsulation
Network layer communication protocols (i.e., IPv4 and IPv6) specify the packet structure and processing used to carry the data from one host to another host.
Operating without regard to the data carried in each packet allows what?
The network layer to carry packets for multiple types of communications between multiple hosts.
How does IP encapsulate the transport layer (the layer just above the network layer) segment or other data?
By adding an IP header
Is used to deliver the packet to the destination host.
IP header
The process of encapsulating data layer by layer enables the services at the different layers to?
Develop and scale without affecting the other layers.
the basic characteristics of IP
Connectionless
Best Effort
Media Independent
IP Characteristic wherein there is no connection with the destination established before sending data packets.
No dedicated end-to-end connection is created by IP before data is sent.
Connectionless
IP Characteristic wherein IP is inherently unreliable because packet delivery is not guaranteed.
With no pre-established end-to-end connection, senders are unaware whether destination devices are present and functional when sending packets, nor are they aware if the destination receives the packet, or if the destination device is able to access and read the packet.
The IP protocol does not guarantee that all packets that are delivered are, in fact, received.
Best effort
IP Characteristic wherein operation is independent of the medium (i.e., copper, fiber-optic, or wireless) carrying the data.
IP operates independently of the media that carry the data at lower layers of the protocol stack
Media Independent
One major characteristic of the media that the network layer considers: 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 the establishment of a maximum size for the packet.
Maximum Transmission Unit (MTU)
A process wherein IPv4 is split up when forwarding it from one medium to another with a smaller MTU. This however causes latency.
Fragmentation
A significant field in the IPv4 header that contains a 4-bit binary value set to 0100 that identifies this as an IPv4 packet.
Version
A significant field in the IPv4 header that is an 8-bit field used to determine the priority of each packet.
The six most significant bits of this field are the differentiated services code point (DSCP) bits and the last two bits are the explicit congestion notification (ECN) bits.
Differentiated Services/DiffServ (DS)
A significant field in the IPv4 header that contains an 8-bit binary value that is used to limit the lifetime of a packet.
The source device of the IPv4 packet sets this initial value. It is decreased by one each time the packet is processed by a router. If this field decrements to zero, the router discards the packet and sends an Internet Control Message Protocol (ICMP) Time Exceeded message to the source IP address.
Because the router decrements this field of each packet, the router must also recalculate the Header Checksum.
Time to Live (TTL)
A significant field in the IPv4 header that is used to identify the next level protocol. This 8-bit binary value indicates the data payload type that the packet is carrying, which enables the network layer to pass the data to the appropriate upper-layer protocol.
Common values include ICMP (1), TCP (6), and UDP (17).
Protocol
A significant field in the IPv4 header that is used to detect corruption in the IPv4 header.
Header Checksum
A significant field in the IPv4 header that contains a 32-bit binary value that represents the source IPv4 address of the packet.
This is always a unicast address.
Source IPv4 Address
A significant field in the IPv4 header that contains a 32-bit binary value that represents the destination IPv4 address of the packet.
The destination IPv4 address is a unicast, multicast, or broadcast address.
Destination IPv4 Address
The two most commonly referenced fields in the packet field.
These fields identify where the packet is coming from and where it is going.
Typically, these addresses do not change while travelling from the source to the destination.
Source and Destination IP addresses.
The fields are used to identify and validate the packet.
The Internet Header Length (IHL)
Total Length
Header Checksum
Fields are used to reorder a fragmented packet (Specifically IPv4 packets to keep track of the fragments)
Identification
Flags
Fragment Offset
IP version that overcomes the limitations of IPv4 and is a powerful enhancement with features that better suit current and foreseeable network demands.
IPv6
Improvements that IPv6 provides
Increased address space - IPv6 addresses are based on 128-bit hierarchical addressing as opposed to IPv4 with 32 bits.
Improved packet handling - The IPv6 header has been simplified with fewer fields.
Eliminates the need for NAT - NAT between a private IPv4 address and a public IPv4 is not needed.
A field in the IPv6 header that contains a 4-bit binary value set to 0110 that identifies this as an IP version 6 packet.
Version
A field in the IPv6 header that is an 8-bit field is equivalent to the IPv4 Differentiated Services (DS) field.
Traffic Class
A field in the IPv6 header that is a 20-bit field that suggests that all packets with the same flow label receive the same type of handling by routers.
Flow Label
A field in the IPv6 header that is a 16-bit field indicates the length of the data portion or payload of the IPv6 packet.
This does not include the length of the IPv6 header, which is a fixed 40-byte header.
Payload Length
A field in the IPv6 header that is the 8-bit field that replaces the IPv4 TTL field.
This value is decremented by a value of 1 by each router that forwards the packet.
When the counter reaches 0, the packet is discarded, and an ICMPv6 Time Exceeded message is forwarded to the sending host.
Unlike IPv4, IPv6 does not include an IPv6 Header Checksum, because this function is performed at both the lower and upper layers.
Hop Limit
A field in the IPv6 header that is the 128-bit field that identifies the IPv6 address of the sending host.
Source IPv6 Address
A field in the IPv6 header that is the 28-bit field that identifies the IPv6 address of the receiving host.
Destination IPv6 Address
An IPv6 may also contain this, which provides optional network layer information
Are placed between the IPv6 header and the payload.
Extension Header (EH)
Octets of the variable length header for IPv4 and IPv6 and the number of header fields for IPv4 and IPv6
IPv4 - 20 octets and 12 basic header fields
IPv6 - 40 octets and 8 basic header fields
