CCNA 1 v7 Modules 8-10 Exam Answers

Communicating Between Networks

Routers and Packet Forwarding

• Routers use the destination IP address to forward a data packet towards its destination.
• A router receives a packet from an interface and determines that the packet needs to be forwarded out another interface.
• The router will create a new Layer 2 Ethernet frame to be sent to the destination.

IP Addressing

• A host can use the IP address 127.0.0.1 to ping the loopback interface.
• The large number of public IPv6 addresses eliminates the need for NAT (Network Address Translation).
• Any host or user can get a public IPv6 network address, which avoids some of the NAT-induced application problems.

Routing Decisions

• A router uses the metric value associated with the destination network to choose the path to the destination when there are multiple routes available.
• The metric value is used to determine the best path to the destination network.

OSI Network Layer

• The OSI network layer provides several services, including:
  • Addressing
  • Encapsulation
  • Routing
  • De-encapsulation
• Error detection, placing frames on the media, and collision detection are functions of the data link layer.

Switch Configuration

• Configuring a switch with a default gateway address allows the switch to forward packets originating from the switch to remote networks.
• The default gateway address is not used to provide Layer 3 routing for PCs connected to the switch.

IP Protocol Characteristics

• The IP protocol is connectionless, meaning it does not require an initial exchange of control information to establish an end-to-end connection before packets are forwarded.
• IP is media independent and does not provide reliable end-to-end delivery by itself.
• User data segmentation is a service provided at the transport layer.

IPv4 Header Fields

• The Time-to-Live (TTL) field in the IPv4 header is used to limit the lifetime of a packet and prevent it from traversing a network endlessly.
• The Protocol field in the IPv4 header identifies the upper-layer protocol the packet is carrying.
• The Differentiated Services (DS) field is used to determine the priority of each packet.

IPv6 Simplified Header

• The IPv6 simplified header offers several advantages over IPv4, including:
  • Better routing efficiency and efficient packet handling
  • No requirement for processing checksums
  • Simplified and more efficient extension header mechanisms### Routing and Forwarding
• Packets are forwarded through different interfaces based on their destination IP addresses.
• A gateway of last resort is used when there is no entry in the routing table for a packet's destination network.
• If a packet's destination network is unknown, it will be forwarded through the gateway of last resort.

Loopback Test

• The loopback test verifies that the host NIC, drivers, and TCP/IP stack are functioning.
• It does not provide information about network connectivity to other hosts.

Routing Table Entries

• Remote routes have a next hop IP address associated with a destination network.
• Directly-connected and local routes do not require a next hop, as they do not need to go through another router.

Host Routing

• Hosts maintain their own local routing table to ensure packets are directed to the correct destination network.
• The local routing table typically contains a route to the loopback interface, a local network route, and a default route.

IPv6 Header Field

• The Flow Label field in the IPv6 header is used to inform routers and switches to maintain the same path for packets in the same conversation.

Address Resolution Protocol (ARP)

• ARP is used to discover the MAC address of a host on the same network.
• ARP requests are sent as broadcasts to all devices on the local link.
• Switches forward ARP requests to all ports except the incoming port.

ARP Cache

• The ARP cache is used to store IPv4 addresses and their corresponding MAC addresses.
• Clearing the ARP cache using the arp -d * command is helpful when a router's configuration changes.

IPv6 Address Resolution

• Neighbor solicitation and neighbor advertisement messages are used in place of ARP for address resolution in IPv6.

Network Security

• ARP spoofing attacks associate IP addresses with incorrect MAC addresses.
• The aim of an ARP spoofing attack is to associate an IP address with the wrong MAC address.

Frame Forwarding

• Switches forward frames based on the destination MAC address.
• If a switch does not know where to send a frame, it will forward it to all ports except the incoming port.

Network Device Access

• Console and AUX ports can be used for local management access to network devices.
• SSH and Telnet are remote access methods that depend on an active network connection.

Router Boot Process

• The boot process of a Cisco router involves three phases: performing the POST and loading the bootstrap program, loading the Cisco IOS software, and loading the startup configuration file.

Network Device Management

• The ip default-gateway command is used to configure a default gateway on a switch.
• The transport input ssh command enables SSH encryption for remote access to a switch.### CCNA 1 v7 Modules 8-10: Communicating Between Networks

Router Configuration

• The three commands needed to password protect the console port are:
  • line console 0
  • password cisco
  • login
• The interface fastethernet 0/0 command is used to access the configuration mode for a specific interface (e.g. Fa0/0)
• The line vty 0 4 command is used to access the configuration mode for Telnet, specifying ports 0 through 4 (maximum of five simultaneous connections)
• The enable secret command is used to apply a password used to access privileged mode on the router

Default Gateway

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

Router Functions

• Two primary functions of a router are:
  • Packet forwarding
  • Path selection
• A router accepts a packet, accesses its routing table, and determines the appropriate exit interface based on the destination address

Router Configuration Files

• The copy running-config startup-config command copies the running-configuration file from RAM into NVRAM, saving it as the startup-configuration file
• This ensures that the configuration details are retained when the router is powered off

ARP Operation

• Two potential network problems that can result from ARP operation are:
  • Manually configuring static ARP associations could facilitate ARP poisoning or MAC address spoofing
  • Network attackers could manipulate MAC address and IP address mappings in ARP messages with the intent of intercepting network traffic
• Large numbers of ARP broadcast messages could cause momentary data communication delays

IPv4 Packet Header

• The protocol field in the IPv4 packet header is used to identify the next level protocol
• The TTL (Time To Live) field in the IPv4 packet header is used to limit the lifetime of a packet
• The header checksum field in the IPv4 packet header is used to detect corruption in the IPv4 header
• The source IPv4 address field in the IPv4 packet header contains a unicast, multicast, or broadcast address
• The version field in the IPv4 packet header contains a 4-bit binary value set to 0100

ARP Properties

• ARP allows hosts on a LAN to send traffic to remote networks by learning the MAC address of the default gateway
• ARP allows MAC addresses of frequently used servers to be fixed in the ARP table through manual configuration
• ARP forces all Ethernet NICs to process an ARP request when the destination MAC address FF-FF-FF-FF-FF-FF appears in the header of the Ethernet frame
• ARP causes a reply only to the source sending an ARP request
• ARP causes the request to be flooded out all ports of a switch except for the port receiving the ARP request