Chapter 8: Network Layer

This is a destination host that is on the same local network as the send host. The source and destination hosts share the same network address.

Local host

True or False: The IP protocol was not designed to track an manage the flow of packets.

True, These functions, if required, are performed by other protocols at other layers, primarily TCP at Layer 4.

True or False: IP operates independently of the media that carry the data at lower layers of the protocol stack.

True, the OSI data link 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.

What IPv4 headers fields had there name and position changed in an IPv6 header?

Type of service Total Length Time-to-Live Protocol

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

Version

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

Version

What IPv4 header fields remain the same in IPv6 header?

Version Source address Destination address

The fields in the IPv6 header include the follwoing:

Version Traffic Class Flow Label Payload Length Next Header Hop Limit Source IPv6 Address Destination IPv6 Address

True or False: Fragmentation causes latency

True

True or False: IP was designed as a protocol with low overhead.

True,

What is the loopback address used for IPv4?

127.0.0.1

What is the total length of a IPv6 packet header?

40 bytes or 40 octets

What is the loopback address used for IPv6?

::1

Is the default gateway required if the you want to communicate outside the network?

A default gateway is required to send traffic outside of the local network.

What is a default route?

A default route is the route or pathway your computer will take when it tries to contact a remote network.

What will a routing table typically include if the default gateway is confiugred?

A default route, which will be the IP address of the default gateway

Why would a router have to fragment an IPv4 packet?

A router may have to fragment an IPv4 packet when forwarding it form one medium to another with a smaller Maximum Transmission Unit (MTU).

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

Addressing end devices

To accomplish end-to-end communications across network boundaries, network layer protocols perform four basic operations:

Addressing end devices Encapsulation Routing De-encapsulation

IP is inherently unreliable because packet delivery is not guranteed

Best Effort

There is no connection with the destination established before sending data packets.

Connectionless

What the three basic characteristics of IP:

Connectionless Best Effort Media Independent

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 preformed 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? (Choose two) Destination IP address protocol Time to Live Source IP address Differentiated Services

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, broadcast, or multicast

Destination IPv4 address

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

Destination IPv6 Address

Formerly called the type of service (ToS) field, 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 of DiffServ (DS)

What two methods in IPv4, are used be a host to obtain IPv4 address of the default gateway?

Either dynamically form Dynamic Host Configuration Protocol (DHCP) or manually configured

With such a larger 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 application that require end-to-end connectivity.

Eliminates the need for NAT

What is the benefit of encapsulating data layer by layer?

Enables the services at the different layers to develop and scale without affecting the other layers. 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

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

It is important to note, that the IP addressing information remains the same from the time the packet leaves the source host until it arrives at the destination host, except when?

Except when translated by the device performing Network Address Translation (NAT) for IPV4.

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

Flow Label

What is the term for splitting up an IP packet when forwarding it from one medium to another medium with a smaller MTU? encapsulation fragmentation segmentation serialization

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 what?

Fragmenting the packet, or fragmentation.

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 Time to Live Protocol Differentiated Services (DS)

Header Checksum

This 8-bit field 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. This indicates that the packet did not reach its destination because the hop limit was exceeded. Unlike IPv4, IPv6 does not include an IPv6 header checksum, because this function is preformed at both the lower an upper layers. This means that Checksum does not need to be recalculated by each router when the decrements the Hop Limit field, which also improves network performance.

Hop Limit

Which three options are major issues associated with IPv4? ( Choose three) IP address depletion Increased network complexity and Internet routing table expansion always on connections lack of end-to-end connectivity global and political boundaries too many IPv4 address available

IP address depletion Increased network complexity and Internet routing table expansion Lack of end-to-end connectivity

What do intermediary devices examine when looking at layer 3 packets?

IP header for network layer addressing

What does it mean that IP is connectionless?

IP is connectionless, meaning that no dedicated end-to-end connection is created by IP before data is sent. For example, Connectionless communication conceptually similar to sending a letter to someone without notifying the recipient in advance.

IPv4 has a limited number of unique public address available. Although there are approximately 4 billion IPv4 address, the increasing number of new IP-enables devices, always-on connections, and the potential growth of less-developed regions have increased the need for more address.

IPv4 address depletion

What are the three major issues with IPv4?

IPv4 address depletion Lack of end-to-end connectivity Increased network complexity

What are the principle network layer communication protocols?

IPv4 and IPv6

Which fields reorder a fragmented packet and keep track of the fragments?

Identification Flags Fragment Offset

What are some reasons why a local host would not be able to reach a remote host?

If there is no default gateway, the default gateway address in not configured, or the default gateway is down.

The IPv6 header has been simplified with fewer fields.

Improved packet handling

Which two options are improvements provided by IPv6 as compared to IPv4? (Choose Two) header supports additional fields for complex packets increased IP address space standardizes the use of NAT Supports class-based networks uses a simpler header to provide improved packet handling

Increased IP address space Uses a simpler header to provide improved packet handling

IPv6 addresses are based on the +128-bit hierarchical addressing as opposed to IPV4 with 32 bits

Increased address space

What are the three improvements that IPv6 provides over IPv4?

Increased address space Improved packet handling Eliminates the need for NAT

While NAT extended the lifespan of IPv4 it was only meant as a transition mechanism to IPv6. NAT in tis various implementation creates additional complexity in the network, creating latency and making troubleshooting more difficult.

Increased network complexity

What does the messaging protocol ICMP stand for?

Internet Control Message Protocol

What fields IPv4 header fields are no longer required in an IPv6 header?

Internet Header Length (IHL) Identification Flags Fragment Offset Header Checksum Options Padding

Which fields in a IPv4 header identify and validate the packet?

Internet Header Length (IHL) Total Length Header Checksum

On a network, a default gateway is usually a router with theses features:

It has a local IP address in the same address range as other hosts on the local network. It can accept data into the local network and forward data out of the local network It routes traffic to other network

What is the IP protocols designed for?

It provides only the functions that are necessary deliver a packet from a source to a destination over an interconnected system of networks.

A host can ping itself by sending a packet to a special IPv4 address of 127.0.0.1 or an IPv6 address of ::1, which is referred to as the loopback interface. Pinging the loopback interface tests TCP/IP protocol stack on the host.

Itself

Another role of the network layer is to direct packets between hosts. A host can send a packet to the following:

Itself Local Host Remote host

Network Address Translation (NAT) is a technology commonly implemented within IPv4 networks. NAT provides way to 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 maximum size of the PDU that each medium can transport. This characteristic is referred to as what?

Maximum Transmission Unit (MTU)

Part of the control communication between the data link layer and the network layer is the establishment of what?

Maximum size for the packet

Operation is independent of the medium (IE copper, fiber, or wireless)

Media Independent

This 8-bit field is equivalent to the IPv4 Protocol field. It indicates the data payload type that the packet is carrying, enabling the network layer to pass the data to the appropriate upper-layer protocol

Next Header

Can IPv6 packets be fragmented by the router?

No

If you do not have a default gateway, can local traffic travel outside of the local network?

No, traffic cannot be forwarded outside the local network.

What does the routing protocols OSPF stand for?

Open Shortest Path First

This 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 fixed 40-byte header.

Payload Length

This field is used to identify the next level protocol. This 8-bit binary vale 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)? Header Checksum Time to Live Protocol Differentiated Services

Protocol

What the is the purpose of the network layer or layer 3?

Provides services to allow end devices to exchange data across networks.

This is a destination host on a remote network. The source and destination hosts do not share the same network address.

Remote host

Devices that are beyond the local network segment are known as what?

Remote hosts

What devices examine a layer 3 header as it travels across a network to its destination?

Routers and layer 3 switches

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 across many routers before reaching the destination host. Each router a packet crosses to reach the dentation host is called a hop.

Routing

When a source device sends a packet to a remote destination device, then the help what two things are needed?

Routing and a routes

What does it mean to route packte?

Routing is the process of identifying the best path to a destination.

What type of protocols do routers implement?

Routing protocols

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

Source IPv4 address

This 128-bit field identifies the IPv6 address of the sending host.

Source IPv6 Address

In the TC/IP protocol suite, reliability is the role of what protocol at the transport layer?

TCP or Transmission Control Protocol

Which is true of the IPv6 packet header? The Hop Limit field replaces the IPv4 Time to Live field The source and destination IPv69 address change while travelling form source to destination The Time to Live field replaces the DiffServ field The Version field identifies the next header

The Hop Limit field replaces the IPv4 Time To Live field

Why is IP considered best effort/unreliable?

The IP protocol does not guarantee that all packets that are delivers are, in fact received.

How does the network layer determine how lage a packet can be?

The data link layer passes the MTU value up to the network layer and then the network layer determines how large packets can be.

What is the default gateway used for?

The default gateway is the network device (i.e., router or Layer 3 switch) that can route traffic to other networks. If you use the analogy that a network is like a room, then the default gateway is like a doorway. If you want to get to another room or network you need to find the doorway.

In IPv6, how does the source end device determine whether destination IP address on the same network that the source device its self is on?

The local router advertises the local network address (prefix) to all devices on the network.

What is the one major characteristic of the media that the network layer considers?

The maximum size of the PDU that each medium can transport.

What is the minimum size of an IPv4 packet header?

The minimum size is 20 bytes or 20 octets

Unlike the transport layer (OSI Layer 4), which manages the data transport between the processes running on each host, network layer communicating protocols (i.e. IPv4 and IPv6) specify what two things?

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 the network layer to carry packets for multiple types of communications between multiple hosts.

What two methods in IPv6, are used be a host to obtain IPv6 address of the default gateway?

The router advertises the default gateway address or the host can be configured manually

What is the a default gateway?

The router connected to the local network segment is referred to as the default gateway.

Which statement is correct about IPv4 packet header fields? The source and destination IPv4 address remain the same while traveling from source to destination The time to Live field is used to determine the priority of each packet The Total Length and Header Checksum fields are used to reorder a fragmented packet The Version fields identifies the next level protocol

The source and destination IPv4 address remain the same while traveling from source to destination

In IPv4, how does the source end device determine whether destination IP address on the same network that the source device its self is on?

The source device uses its own subnet mask along with its own IPv4 address and the destination IPv4 address to make this determination.

TTL 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 on each time the packet is processed by the 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)

How does the source host a direct the packet to the destination host?

To do this, host end devices create their own routing table. This topic discusses how end devices use routing tables.

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

Traffic Class

Which OSI layer sends segments to be encapsulated in an IPv4 or IPv6 packet? data link network transport session

Transport layer

What OSI layer PDU does the network layer encapsulate?

Transport layer PDU/Segment

Which delivery method does not guarantee that the packet will be delivered fully without errors? connectionless best effort media independent

best effort

Which layer is responsible for taking an IP packet and preparing it for transmission over the communication medium? physical layer network layer data link layer transport layer

data link layer

Which is true of the IPv6 header? (Choose two) It consists of 20 octets it consists of 40 octets it contains 8 header fields it contains 12 header fields

it consists of 40 octets it contains 8 header fields