CNA 101 - Module 8 - Network Layer, CNA 101 - Module 7 - Ethernet Switching

Ethernet Addressing

The Ethernet frame includes both a source and destination MAC address to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN.

Type / Length

This 2-byte field identifies the upper layer protocol encapsulated in the Ethernet frame. Common values are, in hexadecimal, 0x800 for IPv4, 0x86DD for IPv6 and 0x806 for ARP.

64-1518

What are the two sizes (minimum and maximum) of an Ethernet frame?

netstat - l route print

Which two commands could be entered on a Windows host to view its IPv4 and IPv6 routing table? (Choose two.) netroute -l netstat -r print route route print print net

8.2.2

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The packet will be sent directly to the destination host

A computer has to send a packet to a destination host in the same LAN. How will the packet be sent? The packet will be sent to the default gateway first, and then, depending on the response from the gateway, it may be sent to the destination host. The packet will be sent directly to the destination host. The packet will first be sent to the default gateway, and then from the default gateway it will be sent directly to the destination host. The packet will be sent only to the default gateway.

create a new Layer 2 Ethernet frame to be sent to the destination

A router receives a packet from the Gigabit 0/0 interface and determines that the packet needs to be forwarded out the Gigabit 0/1 interface. What will the router do next? route the packet out the Gigabit 0/1 interface create a new Layer 2 Ethernet frame to be sent to the destination look into the ARP cache to determine the destination IP address look into the routing table to determine if the destination network is in the routing table

Connectionless

Characteristics of IP IP requires no initial exchange of control information to establish an end-to-end connection before packets are forwarded.

The MTU is passed to the network layer by the data link layer.

How does the network layer use the MTU value? The network layer depends on the higher level layers to determine the MTU. The network layer depends on the data link layer to set the MTU, and adjusts the speed of transmission to accommodate it. The MTU is passed to the network layer by the data link layer. To increase speed of delivery, the network layer ignores the MTU.

Ethernet frame Ethernet Addressing Ethernet Error detection

IEEE 802.3 data encapsulation includes the following:

1. Preamble and SFD (Start Frame Delimiter) 2. Destination MAC Address 3. Source MAC Address 4. Type/Length 5. Data 6. FCS (Frame Check Sum)

Identify the fields

Increased address space

Improvements that is provided by IPv6 IPv6 addresses are based on 128-bit hierarchical addressing as opposed to IPv4 with 32 bits.

Improved packet handling

Improvements that is provided by IPv6 The IPv6 header has been simplified with fewer fields.

Eliminates the need for NAT

Improvements that is provided by IPv6 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.

IPv4 address depletion

Limitations of IPv4 IPv4 has a limited number of unique public addresses available.

Lack of end-to-end connectivity

Limitations of IPv4 Network Address Translation (NAT) is a technology commonly implemented within IPv4 networks.

NAT

Limitations of IPv4 Provides a way for multiple devices to share a single public IPv4 address.

The IPv4 address of an internal network host is hidden because IPv4 address is shared.

Limitations of IPv4 This can be problematic for technologies that require end-to-end connectivity.

Increased network complexity

Limitations of IPv4 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.

Ethernet Error detection

The Ethernet frame includes a frame check sequence (FCS) trailer used for error detection.

Frame Check Sequence Field

The Frame Check Sequence (FCS) field (4 bytes) is used to detect errors in a frame. It uses a cyclic redundancy check (CRC). The sending device includes the results of a CRC in the FCS field of the frame. The receiving device receives the frame and generates a CRC to look for errors. If the calculations match, no error occurred. Calculations that do not match are an indication that the data has changed; therefore, the frame is dropped. A change in the data could be the result of a disruption of the electrical signals that represent the bits.

Preamble and Start Frame Delimiter Fields

The Preamble (7 bytes) and Start Frame Delimiter (SFD), also called the Start of Frame (1 byte), fields are used for synchronization between the sending and receiving devices. These first eight bytes of the frame are used to get the attention of the receiving nodes. Essentially, the first few bytes tell the receivers to get ready to receive a new frame.

Source MAC Address Field

This 6-byte field identifies the originating NIC or interface of the frame.

Destination MAC Address Field

This 6-byte field is the identifier for the intended recipient. As you will recall, this address is used by Layer 2 to assist devices in determining if a frame is addressed to them. The address in the frame is compared to the MAC address in the device. If there is a match, the device accepts the frame. Can be a unicast, multicast or broadcast address.

Data Field

This field (46 - 1500 bytes) contains the encapsulated data from a higher layer, which is a generic Layer 3 PDU, or more commonly, an IPv4 packet. All frames must be at least 64 bytes long. If a small packet is encapsulated, additional bits called a pad are used to increase the size of the frame to this minimum size.

Ethernet frame

This is the internal structure of the Ethernet frame.

default route

This type of route is also known as a gateway of last resort. static route remote route default route directly connected route

True

True or False? A router can be configured with a combination of both static routes and a dynamic routing protocol. True False

The source Layer 2 address of incoming frames.

What addressing information is recorded by a switch to build its MAC address table?

1. It is responsible for Media Access Control. 2. It adds a header and trailer to form an OSI Layer 2 PDU.

What are two functions or operations are performed by the MAC sublayer?

a route learned dynamically from OSPF

What does a code of "O" indicate next to a route in the routing table? a directly connected route a route with an administrative distance of 0 a gateway of last resort a route learned dynamically from OSPF

The frame is dropped.

What happens to runt frames received by a Cisco Ethernet switch?

source and destination IP address

What information is added during encapsulation at OSI Layer 3? source and destination MAC source and destination application protocol source and destination port number source and destination IP address

1. Controls access to the media. 2. checks for errors in received bits. 3. Uses CSMA/CD or CSMA/CA to support Ethernet technology.

What is a function of the MAC sublayer?

A feature that detects Ethernet cable type.

What is auto-MDIX?

show ip route

What is the command used on a Cisco IOS router to view the routing table? netstart -r route print show ip route show routing table

01-00-5E-xx-xx-xx

What is the special value assigned to the first 24 bits of a multicast MAC address?

Fragmentation

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

They must be globally unique.

What statement describes a characteristic of MAC addresses?

An address that reaches a specific group of hosts.

What type of address is 01-00-5E-0A-00-02?

to relieve IPv4 address depletion

What was the reason for the creation and implementation of IPv6? to make reading a 32-bit address easier to relieve IPv4 address depletion to provide more address space in the Internet Names Registry to allow NAT support for private addressing

It will discard the frame.

What will a host on an Ethernet network do if it receives a frame with a destination MAC address that does not match its own MAC address?

Upper-Layer connection-oriented protocols keep track of the date received and can request retransmission from upper-layer protocols on the sending host.

When a connectionless protocol is in use at a lower layer of the OSI model, how is missing data detected and retransmitted if necessary? Connectionless acknowledgements are used to request retransmission. Upper-layer connection-oriented protocols keep track of the data received and can request retransmission from the upper-level protocols on the sending host. Network layer IP protocols manage the communication sessions if connection-oriented transport services are not available. The best-effort delivery process guarantees that all packets that are sent are received.

the destination IP address

When a router receives a packet, what information must be examined in order for the packet to be forwarded to a remote destination? destination MAC address source IP address the destination IP address source MAC address

127.0.0.1

Which IPv4 address can a host use to ping the loopback interface? 126.0.0.1 127.0.0.0 126.0.0.0 127.0.0.1

Transport Layer

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

Destination IP Address Source IP Address

Which 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 (DS)

The IPv6 header is simpler than the IPv4 header is, which improves packet handling.

Which characteristic describes an IPv6 enhancement over IPv4?​ IPv6 addresses are based on 128-bit flat addressing as opposed to IPv4 which is based on 32-bit hierarchical addressing. The IPv6 header is simpler than the IPv4 header is, which improves packet handling. Both IPv4 and IPv6 support authentication, but only IPv6 supports privacy capabilities. The IPv6 address space is four times bigger than the IPv4 address space.​

netstat -r

Which command can be used on a Windows host to display the routing table? netstat -s show ip route netstat -r tracert

LLC

Which data link sublayer controls the network interface through software drivers?

LLC

Which data link sublayer works with the upper layers to add application information for delivery of data to higher level protocols?

The default gateway address is the IP address of the router on the local network.

Which default gateway statement is true? A default gateway is required to send packets to other hosts on the local network. The default gateway address is the IP address of a switch on a remote network. The default gateway address is the IP address of the router on the local network. Traffic can only be forwarded outside the local network if there is no default gateway.

Best Effort

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

Destination Address

Which field in an IPv4 packet header will typically stay the same during its transmission? Flag Time-to-Live Packet Length Destination Address

Hop Limit

Which field in an IPv6 packet is used by the router to determine if a packet has expired and should be dropped? TTL Hop Limit Address Unreachable No Route to Destination

Protocol

Which field includes common values such as ICMP (1), TCP (6), and UDP (17)? Header Checksum Time to Live Protocol Differentiated Services (DS)

Header Checksum

Which field is used to detect corruption in the IPv4 header? Header Checksum Time to Live Protocol Differentiated Services (DS)

It communicates with upper protocol layers.

Which function or operation is performed by the LLC sublayer?

destination IP address

Which information is used by routers to forward a data packet toward its destination? source IP address destination IP address source data-link address destination data-link address

They are manually configured

Which is a characteristic of static routes? They are manually configured. They are advertised to directly connected neighbors. They are appropriate when there are many redundant links. They automatically adjust to a change in network topology.

it consists of 40 octets it contains 8 header fields

Which is true of the IPv6 header? it consists of 20 octets. it consists of 40 octets. it contains 8 header fields. it contains 12 header fields.

The hop limit field replaces the IPv4 Time to Live field

Which is true of the IPv6 packet header? The Hop Limit field replaces the IPv4 Time to Live field. The Source and Destination IPv6 addresses change while travelling from source to destination. The Time to Live field replaces the DiffServ field. The Version field identifies the next header.

Data Link Layer

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

Switch

Which network device has the primary function to send data to a specific destination based on the information found in the MAC address table?

Switch

Which network device makes forwarding decisions based on the destination MAC address that is contained in the frame?

EtherType Field

Which part of an Ethernet Frame describes the higher-layer protocol that is encapsulated?

Preamble

Which part of an Ethernet Frame notifies the receiver to get ready for a new frame?

Data Field

Which part of an Ethernet Frame uses a pad to increase the frame field to at least 64 bytes?

FCS (Frame Check Sequence)

Which part of an Ethernet frame detects errors in the frame?

Local hosts can reach each other without the need of a router.

Which statement about host forwarding decisions is true? A host cannot ping itself. A remote destination host is on the same local network as the sending host. Local hosts can reach each other without the need of a router. Routing is enabled on switches to discover the best path to a destination.

IPv4 has a 32-bit address space

Which statement accurately describes a characteristic of IPv4? All IPv4 addresses are assignable to hosts.​ IPv4 has a 32-bit address space.​ An IPv4 header has fewer fields than an IPv6 header has.​ IPv4 natively supports IPsec.​

The source and destination IPv4 addresses remain the same while travelling from source to destination.

Which statement is correct about IPv4 packet header fields? The source and destination IPv4 addresses remain the same while travelling 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 field identifies the next level protocol.

The first three bytes are used by the vendor assigned OUI.

Which statement is true about MAC addresses?

IP address depletion Increased network complexity and Internet routing lack of end-to-end connections

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 addresses available

1. It is supported by IEEE 802.3 standards. 2. It uses the CSMA/CD access control method.

Which two characteristics describe Ethernet technology?

Increased the IP address space Uses a simpler header to provide 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 the IP address space standardizes the use of NAT supports class-based networks uses a simpler header to provide improved packet handling