[8-10] | Communicating Between Networks | FODC
In the early 1990s, the Internet Engineering Task Force (IETF) grew concerned about the issues with IPv4 and began to look for a replacement. This activity led to the development of IP version ____________
6 (IPv6)
End devices must be configured with a unique IP address for identification on the network.
Addressing end devices
IP is inherently unreliable because packet delivery is not guaranteed.
Best Effort
There is no connection with the destination established before sending data packets.
Connectionless
These are the basic characteristics of IP:
Connectionless, Best Effort, and Media Independent.
Which layer is responsible for taking an IP packet and preparing it for transmission over the communications medium?
Data Link Layer
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 is de-encapsulated by the network layer, the resulting Layer 4 PDU is passed up to the appropriate service at the transport layer. The de-encapsulation process is performed by the destination host of the IP packet.
De-encapsulation
What are the two most commonly referenced fields in an IPv4 packet header that indicate where the packet is coming from and where it is going?
Destination IP Address Source IP Address
This 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
Formerly called the type of service (ToS) field, the DS field is an 8-bit field used to determine the priority of each packet. The six most significant bits of the DiffServ field are the differentiated services code point (DSCP) bits and the last two bits are the explicit congestion notification (ECN) bits.
Differentiated Services or DiffServ (DS)
With such a large number of public IPv6 addresses, NAT between a private IPv4 address and a public IPv4 is not needed. This avoids some of the NAT-induced problems experienced by applications that require end-to-end connectivity.
Eliminates the need for NAT
The network layer encapsulates the protocol data unit (PDU) from the transport layer into a packet. The encapsulation 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
This is used to detect corruption in the IPv4 header.
Header Checksum
Which field is used to detect corruption in the IPv4 header?
Header Checksum
Packets may arrive at the destination corrupted, out of sequence, or not at all.__ provides no capability for packet retransmissions if errors occur.
IP
The protocol was not designed to track and manage the flow of packets. These functions, if required, are performed by other protocols at other layers, primarily TCP at Layer 4.
IP
__ was designed as a protocol with low overhead. It provides only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks.
IP
The _________________ information remains the same from the time the packet leaves the source host until it arrives at the destination host, except when translated by the device performing Network Address Translation (NAT) for IPv4.
IP addressing
The binary values of each field identify various settings of the _____________
IP packet
This is because while ________________ are sent with information about the location of delivery, they do not contain information that can be processed to inform the sender whether delivery was successful.
IP packets
IPv6 overcomes the limitations of _____ and is a powerful enhancement with features that better suit current and foreseeable network demands.
IPv4
_____ is one of the primary network layer communication protocols
IPv4
IPv4 has a limited number of unique public addresses available. Although there are approximately 4 billion IPv4 addresses, the increasing number of new IP-enabled devices, always-on connections, and the potential growth of less-developed regions have increased the need for more addresses.
IPv4 address depletion
Through the years, additional protocols and processes have been developed to address new challenges. However, even with changes, IPv4 still has three major issues:
IPv4 address depletion Lack of end-to-end connectivity Increased network complexity
The _______________ is used to ensure that this packet is delivered to its next stop on the way to its destination end device.
IPv4 packet header
An ______________________ consists of fields containing important information about the packet. These fields contain binary numbers which are examined by the Layer _ process.
IPv4 packet header, 3
Other fields are used to reorder a fragmented packet. Specifically, the IPv4 packet uses _______________, ____________, and ________________ to keep track of the fragments. A router may have to fragment an IPv4 packet when forwarding it from one medium to another with a smaller MTU.
Identification, Flags, and fragment Offset fields
The IPv6 header has been simplified with fewer fields.
Improved packet handling
IPv6 addresses are based on 128-bit hierarchical addressing as opposed to IPv4 with 32 bits.
Increased address space
Improvements that IPv6 provides include the following:
Increased address space Improved packet handling Eliminates the need for NAT
While NAT has extended the lifespan of IPv4 it was only meant as a transition mechanism to IPv6. NAT in its various implementation creates additional complexity in the network, creating latency and making troubleshooting more difficult.
Increased network complexity
Network Address Translation (NAT) is a technology commonly implemented within IPv4 networks. NAT provides a way for multiple devices to share a single public IPv4 address. However, because the public IPv4 address is shared, the IPv4 address of an internal network host is hidden. This can be problematic for technologies that require end-to-end connectivity.
Lack of end-to-end connectivity
The IP header is examined by __________________________________________ as it travels across a network to its destination.
Layer 3 devices (i.e., routers and Layer 3 switches)
The maximum size of the PDU that each medium can transport.
Maximum transmission unit (MTU)
Operation is independent of the medium (i.e., copper, fiber-optic, or wireless) carrying the data.
Media Independent
The ________________ layer is responsible for taking an IP packet and preparing it for transmission over the communications medium. This means that the delivery of IP packets is not limited to any particular medium.
OSI data link
Other network layer protocols include routing protocols such as:
Open Shortest Path First (OSPF) Messaging protocols such as Internet Control Message Protocol (ICMP).
This field 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
Which field includes common values such as ICMP (1), TCP (6), and UDP (17)?
Protocol
The routing performed by these intermediary devices examines the network layer addressing in the packet header. In all cases, the data portion of the packet, that is, the encapsulated transport layer PDU or other data, remains unchanged during the network layer processes.
Routers
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
This contains a 32-bit binary value that represents the source IPv4 address of the packet. The source IPv4 address is always a unicast address.
Source IPv4 Address
In the TCP/IP protocol suite, reliability is the role of the ___ protocol at the transport layer.
TCP
What three fields are used to identify and validate the packet.
The Internet Header Length (IHL) Total Length Header Checksum
Which statement is correct about IPv4 packet header fields?
The source and destination IPv4 addresses remain the same while travelling from source to destination
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 TTL value. It is decreased by one each time the packet is processed by a router. If the TTL 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 the TTL of each packet, the router must also recalculate the Header Checksum.
Time to Live (TTL)
Which OSI layer sends segments to be encapsulated in an IPv4 or IPv6 packet?
Transport Layer
IPv6 packets cannot be fragmented by the router. T/F
True
IPv6 will eventually replace IPv4. T/F
True
The 32-bit IPv4 address space provides approximately 4,294,967,296 unique addresses. IPv6 address space provides 340,282,366,920,938,463,463,374,607,431,768,211,456, or 340 undecillion addresses. This is roughly equivalent to every grain of sand on Earth. T/F
True
IP also does not require additional fields in the header to maintain an established connection. This process greatly reduces the overhead of IP. T/F
True, However, 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 process of encapsulating data layer by layer enables the services at the different layers to develop and scale without affecting the other layers. T/F
True, This means the transport layer segments can be readily packaged by IPv4 or IPv6 or by any new protocol that might be developed in the future.
If out-of-order packets are delivered, or packets are missing, then applications using the data, or upper layer services, must resolve these issues. T/F
True, this allows IP to function very efficiently.
___________ means that IP does not have the capability to manage and recover from undelivered or corrupt packets.
Unreliable
Contains a 4-bit binary value set to 0100 that identifies this as an IPv4 packet.
Version
Significant fields in the IPv4 header include the following:
Version Differentiated Services or DiffServ (DS) Header Checksum Time to Live (TTL) Protocol Source IPv4 Address Destination IPv4 Address
Which delivery method does not guarantee that the packet will be delivered fully without errors?
best effort
IP is __________________________, meaning that no dedicated end-to-end connection is created by IP before data is sent. _________________ communication is conceptually similar to sending a letter to someone without notifying the recipient in advance.
connectionless
Connectionless _____ communications work on the same principle. IP requires no initial exchange of control information to establish an end-to-end connection before packets are forwarded.
data
IP packets can be communicated as ______________ over copper cable, as optical signals over fiber, or _______________ as radio signals.
electronic signals, wirelessly
What is the term for splitting up an IP packet when forwarding it from one medium to another medium with a smaller MTU?
fragmentation
In some cases, an intermediate device, usually a router, must split up an IPv4 packet when forwarding it from one medium to another medium with a smaller MTU. This process is called _______________________
fragmenting the packet, or fragmentation.
Fragmentation causes _______.
latency
IP operates independently of the media that carry the data at lower _____ of the protocol stack.
layers
IP version 4 (IPv4) and IP version 6 (IPv6) are the principle ______ _________ communication protocols.
network layer
The ___________________________, or OSI Layer 3, provides services to allow end devices to exchange data across networks.
network layer
The data link layer passes the MTU value up to the ______________. The _______________ then determines how large packets can be.
network layer
Unlike the transport layer (OSI Layer 4), which manages the data transport between the processes running on each host, _________________________________ (i.e., IPv4 and IPv6) specify the packet structure and processing used to carry the data from one host to another host.
network layer communication protocols
Part of the control communication between the data link layer and the network layer is the establishment of a maximum size for the ____________.
packet
Protocol header diagrams, which are read left to right, and top down, provide a visual to refer to when discussing _______________
protocol fields.
IP does not guarantee that all sent packets will be received. Other _____________ manage the process of tracking packets and ensuring their delivery.
protocols
The IP protocol does not guarantee that all packets that are delivered are, in fact, __________.
received
Routers implement ____________ protocols to route packets between networks.
routing
The two most commonly referenced fields are the __________ and ______________. These fields identify where the packet is coming from and where it is going.
source, destination IP addresses. Typically, these addresses do not change while travelling from the source to the destination.
IP encapsulates the __________________ (the layer just above the network layer) segment or other data by adding an IP header. The IP header is used to deliver the packet to the destination host.
transport layer
