Ch. 5 Ethernet & Ch. 6 Network Layer

The binary number 0000 1010 can be expressed as ____ in hexadecimal.

0A

The two primary addresses assigned to a device on an Ethernet LAN:

1) *physical address* (the MAC address for ethernet NIC communications) 2) *logical address* (the IP address for sending the packet from source to destination)

What two functions does ARP provide?

1) resolves IPv4 addresses to MAC addresses 2) maintains a table of mappings Address Resolution Protocol

Ethernet supports data bandwidths of:

10 Mb/s 100 Mb/s 1000 Mb/s (1 Gb/s) 10,000 Mb/s (10 Gb/s) 40,000 Mb/s (40 Gb/s) 100,000 Mb/s (100 Gb/s)

Which IPv4 address can a host use to ping the loopback interface?

127.0.0.1 is the loopback address

What is the decimal equivalent of the hexadecimal value of 3F?

63

The minimum Ethernet frame size is _____ bytes. Anything smaller than that should be considered a "runt frame."

64 bytes Ethernet II and IEEE 802.3 standards define the minimum frame size as 64 bytes and the maximum as 1518 bytes.

The MAC address is often referred to as a what?

A burned-in address (BIA) because historically this address is burned into ROM on the NIC.

What is a hop?

A hop is an intermediary Layer 3 device that a packet has to traverse to reach its destination. ex. In this case, the number of hops a packet has to traverse from PC-1 to PC-4 is three, as there are three routers from source to destination.

What are the functionalities of the data link layer?

Addressing, framing, and accessing the media

When transporting data from real-time applications, such as streaming audio and video, which field in the IPv6 header can be used to inform the routers and switches to maintain the same path for the packets in the same conversation?

Flow Label The Flow Label in IPv6 header is a 20-bit field that provides a special service for real-time applications. This field can be used to inform routers and switches to maintain the same path for the packet flow so that packets will not be reordered.

Which key combination allows a user to abort setup mode?

Ctrl-C The setup mode can be interrupted at any time using the *Ctrl-C* key combination.

H2 has sent a broadcast message to all of the hosts. If host H1 wants to reply to the broadcast message, which statement is true?

H1 sends a unicast message to H2, and the switch forwards it directly to H2.

In order for routers to be reachable, the router interface must be configured. (T or F)

True.

When the store-and-forward method of switching is in use, what part of the Ethernet frame is used to perform an error check?

CRC in the trailer The *cyclic redundancy check (CRC)* part of the trailer is used to determine if the frame has been modified during transit.​ If the integrity of the frame is verified, the frame is forwarded. If the integrity of the frame cannot be verified, then the frame is dropped.

The 4 basic processes of the Network Layer

IP addressing for end devices (hierarchical addressing and routing), encapsulation, routing, and de-encapsulation

If there are two or more possible routes to the same destination, the _____________ is used to determine which route is used in the routing table.

If there are two or more possible routes to the same destination, the *metric* is used to decide which route appears in the routing table.

Which action is taken by a Layer 2 switch when it receives a Layer 2 broadcast frame?

It sends the frame to all ports except the port on which it received the frame.

What are the two sublayers of the data link layer?

LLC and MAC sublayers

The Ethernet ______ sublayer is responsible for communicating directly with the physical layer.

MAC

A router may have to fragment a packet when forwarding it from one medium to another medium that has a smaller ___________.

MTU (maximum transmission unit)

The acronym ________ is used to define the process that allows multiple devices to share a single routable IP address.

NAT or Network Address Translation is the process of modifying the IP packet header information on packets going outside the corporate network. Corporate networks typically use private addresses on the inside LAN and need a public address to be able to communicate through the WAN.

All MAC addresses assigned to a NIC or other Ethernet device must use that vendor's assigned ____ as the first 3 bytes

OUI (organizationally unique identifier)

How does the network layer use the MTU value?

The MTU is passed to the network layer by the *data link layer*. The data link layer indicates to the network layer the MTU for the medium that is being used. The network layer uses that information to determine how large the packet can be when it is forwarded. When packets are received on one medium and forwarded on a medium with a smaller MTU, the network layer device can fragment the packet to accommodate the smaller size.

Within a production network, what is the purpose of configuring a switch with a default gateway address?

The default gateway address is used to forward packets originating from the switch to remote networks. A default gateway address allows a switch to forward packets that originate on the switch to remote networks. A default gateway address on a switch does not provide Layer 3 routing for PCs that are connected on that switch. A switch can still be accessible from Telnet as long as the source of the Telnet connection is on the local network.

What is the destination MAC address of the Ethernet frame as it leaves the web server if the final destination is PC1?

The destination MAC address is used for local delivery of Ethernet frames. The MAC (Layer 2) address changes at each network segment along the path. As the frame leaves the web server, it will be delivered by using the MAC address of the *default gateway*.

Ethernet is a _________-_______ method of networking.

contention-based a contention-based method means that any device can try to transmit data across the shared medium whenever it has data to send.

Which value, that is contained in an IPv4 header field, is decremented by each router that receives a packet?

Time-to-Live When a router receives a packet, the router will decrement the *Time-to-Live (TTL)* field by one. When the field reaches zero, the receiving router will discard the packet and will send an ICMP Time Exceeded message to the sender.

In Ethernet, different MAC addresses are used for Layer 2 unicast, multicast, and broadcast communications. (T or F)

True

PC1 issues an ARP request because it needs to send a packet to PC3. In this scenario, what will happen next?

When a network device has to communicate with a device on another network, it broadcasts an ARP request asking for the default gateway MAC address. The default gateway (RT1) unicasts an ARP reply with the Fa0/0 MAC address.

What happens when a router receives a packet to be delivered?

When a router, such as the default gateway, receives a packet, it examines the destination IP address to determine the destination network. The routing table of a router stores information about directly-connected routes and remote routes to IP networks. If the router has an entry in its routing table for the destination network, the router forwards the packet. If no routing entry exists, the router may forward the packet to its own default route if one is configured, or it will drop the packet.

The Layer 2 Ethernet frame contains:

a destination MAC address and a source MAC address

The Layer 3 IP packet contains:

a source IP address and a destination IP address

ARP spoofing/poisioning

a technique used by an attacker to reply to an ARP request for an IPv4 address belonging to another device, such as the default gateway. The attacker sends an ARP reply with its own MAC address which is added to the sender's ARP table and the packets are sent to the attacker.

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

an address that reaches a *specific group of hosts* The multicast MAC address is a special value that begins with *01-00-5E* in hexadecimal. It allows a source device to send a packet to a group of devices.

How is an Ethernet MAC address expressed?

as a 48-bit binary value in 12 hexadecimal digits (4 bits per hexadecimal digit) -the same as IPv6 addresses

On Ethernet networks, the hexadecimal address FF-FF-FF-FF-FF-FF represents the ____________ MAC address.

broadcast

Routing table entries can be configured _________ on each router to provide ______ routing, or the routers may communicate route information __________ between each other using a _____________.

can be configured *manually* on each router to provide *static* routing, or routers may communicate information *dynamically* using a *routing protocol*

What do Ethernet switches do?

consult a MAC address table (or CAM table) to make a forwarding decision for each frame. Switches *learn* and *forward* the frames that enter them.

Autonegotiation

enables two devices to automatically exchange information about speed and duplex capabilities

How do you configure a router interface?

enter interface configuration mode enable conf t *int g0/0* use interface type and number

During the boot process, where will the router bootstrap program look for the IOS image by default?

flash The IOS image is typically stored in *flash* memory. If the image is not in flash memory when the router boots, the router bootstrap program can look for it on a TFTP server.

Data encapsulation provides what three primary functions?

frame delimiting- to ID a frame (increases synchronization) addressing- allows for data link layer addressing error detection- each frame contains a trailer that detects any errors in transmission

What is the multicast group IP address range?

from 224.0.0.0- 239.255.255.255

When is CSMA/CD used?

in half-duplex Ethernet LANs to detect and resolve collisions.

All MAC addresses with the same OUI must be assigned a unique value in the ______________.

last 3 bytes

LLC sublayer

logical link control- handles communication between upper (networking software) and lower layers (device hardware) takes the network protocol data (usually an IPv4 packet) and transforms it to be delivered by the physical layer implemented by driver *software* for the NIC

Which portion of the network layer address does a router use to forward packets?

network portion

What are two functions that are provided by the network layer?

providing end devices with a unique network identifier directing data packets to destination hosts on other networks The network layer is primarily concerned with passing data from a source to a destination on another network. IP addresses supply unique identifiers for the source and destination. The network layer provides connectionless, best-effort delivery. Devices rely on higher layers to supply services to processes.

What is the primary purpose of ARP?

resolve IPv4 addresses to MAC addresses

OSI Layer 3 provides

services to allow end devices to exchange data across the network

A Layer 2 switch is used to switch incoming frames from a 1000BASE-T port to a port connected to a 100Base-T network. Which method of memory buffering would work best for this task?

shared memory buffering With *shared memory buffering*, the number of frames stored in the buffer is restricted only by the size of the entire memory buffer and not limited to a single port buffer. This permits larger frames to be transmitted with fewer dropped frames. This is important to asymmetric switching, which applies to this scenario, where frames are being exchanged between ports of different rates. With *port-based memory buffering*, frames are stored in queues that are linked to specific incoming and outgoing ports making it possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port.

Advantages of IPv6 over IPv4

simplified header offers better routing efficiency, simplified extension headers, capability for per-flow processing and increases the number of available IP addresses (bc it is 128 bit addressing)

When a switch configuration includes a user-defined error threshold on a per-port basis, to which switching method will the switch revert when the error threshold is reached?

store-and-forward When the *store-and-forward* switching method is used, the switch receives the complete frame before forwarding it on to the destination. In contrast, a *cut-through* switch forwards the frame once the destination Layer 2 address is read.

When the computer starts up, what is the first thing the NIC does?

the NIC copies the MAC address from ROM (read-only memory) into RAM (random access memory)

IEEE 802.2. and 802.3

the family of networking technologies that make up Ethernet are defined in these standards 802.3 - physical layer and MAC data link layer 802.2 - LLC data link layer

MAC sublayer

the lower sublayer of the data link layer that encapsulates data and does Media Access Control (MAC) implemented by *hardware* typically in the computer NIC. assembles frames being transmitted (sent up) and disassembles frames being received (sent down) MAC layer adds a header and trailer to the network layer PDU (frame) and places frames on the media and removes frames from the media.

Ethernet is now what? And it operates at the _________ layer and _________ layer.

the predominant LAN technology in the world and is a high bandwidth and full-duplex technology operates at the data link layer and the physical layer