Networking Basics Module 12 – 14 Checkpoint Test Online

Hint

The default gateway for a PC is the closest networking device that can forward traffic to other networks. If a PC has an incorrect or nonexistent default gateway address, it will not be able to communicate with devices in remote networks. However, communication would occur between devices in the same network with or without a default gateway.

Hint

Network address translation (NAT) implemented on the home network router enables privately addressed devices to share a registered public IP address that can be routed over the internet.

Hint

Network Address Translation (NAT) is a technology that operates on a wireless router and allows all LAN hosts to share the single internet routable address configured on the external interface of the wireless router. All LAN hosts can communicate at the same time using this single internet assigned IP address.

Hint

When a host needs to send a message to another host located on the same network, it can forward the message directly. However, when a host needs to send a message to a remote network, it must use the router, also known as the default gateway. This is because the data link frame address of the remote destination host cannot be used directly. Instead, the IP packet has to be sent to the router (default gateway) and the router will forward the packet toward its destination. Therefore, if the default gateway is incorrectly configured, the host can communicate with other hosts on the same network, but not with hosts on remote networks.

Hint

On a home router, NAT converts the source address in the IP packet from the internal private IP address to a registered public IP address assigned to the external interface on the router before sending it out over the internet.

Hint

The default gateway address is used to forward packets to remote networks. The IP address of the host must be correct because the user can reach other hosts on the same network. The TCP/IP protocol stack is correct because of verified communication to hosts on the same network. The end device could be incorrectly configured, but the most likely cause of the issue is a wrong address for the default gateway.

Hint

Because host A does not have the MAC address of the default gateway in the ARP table, host A sends an ARP broadcast. The ARP broadcast would be sent to every device on the local network. Hosts B, C, and router R1 would receive the broadcast. Router R1 would not forward the message.

Hint

ARP requests are sent when a host does not have an IP to MAC mapping for a destination in the ARP cache. ARP requests are sent to the Ethernet broadcast of FF:FF:FF:FF:FF:FF. In this example because the address of the remote host is unknown, an ARP request is sent to the Ethernet broadcast to resolve the MAC address of the default gateway that is used to reach the remote host.

Hint

ARP performs two functions: – To obtain a specific MAC address when an IP address is known, by broadcasting an ARP request message to all devices on a particular Ethernet network – To use the gathered information to create a viewable table of IP address to MAC address mappings

Hint

The purpose of an ARP request is to find the MAC address of the destination host on an Ethernet LAN. The ARP process sends a Layer 2 broadcast to all devices on the Ethernet LAN. The frame contains the IP address of the destination and the broadcast MAC address, FFFF.FFFF.FFFF. The host with the IP address that matches the IP address in the ARP request will reply with a unicast frame that includes the MAC address of the host. Thus the original sending host will obtain the destination IP and MAC address pair to continue the encapsulation process for data transmission.

Hint

The switch ARP table keeps a mapping of Layer 2 MAC addresses to Layer 3 IP addresses. These mappings can be learned by the switch dynamically through ARP or statically through manual configuration.

Hint

The address resolution protocol (ARP) maintains a cache of MAC to IPv4 address mappings on the local computer. If there is no mapping in the cache for a specific IPv4 address, then the ARP process sends an Ethernet broadcast on the local link in an attempt to resolve the destination IPv4 address to a MAC address.

Hint

TCP provides reliable delivery of data. UDP provides unreliable delivery of data. DHCP is used for the automatic assignment of IP addresses. ARP is used to discover the MAC address of a device on the Ethernet network.

Hint

When a router receives a packet, it examines the destination address of the packet and uses the routing table to search for the best path to that network.

Hint

When a router receives a frame on an interface, it strips the header containing the source and destination MAC addresses from the frame. The router checks the routing table to determine the interface to use to send the packet to its destination. The packet is then encapsulated in a new frame, with different header information.

Hint

There are two parts to an a network layer address, the network and host portions. Routers are not concerned about delivering packets to hosts. Routers are concerned with delivering packets to the network that a destination host is a member of.

Hint

When a router receives a frame on an interface, it strips the Layer 2 frame header information from the frame. It checks the routing table to determine which interface to use to send the packet to its destination. Once the interface is known, the packet is encapsulated with a new frame header containing different source and destination MAC addresses.

Hint

Routers connect multiple networks, determine the best path to send packets, and forward packets based on a destination IP address.

Hint

Routers use routing tables to store information. Routing tables contain the addresses of networks and the best path to reach those networks.

Hint

The default gateway is used to route packets destined for remote networks. The default gateway IP address is the address of the first Layer 3 device (the router interface) that connects to the same network.