Which field in a routers routing table identifies an IP address of the next router to forward packet?

What is the purpose of the network layer in data communications?

• Addressing End Devices - End devices must be configured with a unique IP address for identification on the network.
• Encapsulation - 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.
• Routing - The network layer provides services to direct 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 cross many intermediary devices before reaching the destination host. Each router a packet crosses to reach the destination host is called a hop.
• De-encapsulation - 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.

What is the role of the major header fields in the IPv4 and IPv6 packets?

IPv4 -

• Version - Contains a 4-bit binary value set to 0100 that identifies this as an IP version 4 packet.
• Differentiated Services - Formerly called the Type of Service field, the DS field is an 8-bit field used to determine the priority
  of each packet. 
• Time-to-Live (TTL) - Contains an 8-bit binary value that is used to limit the lifetime of a packet.  The packet sender sets the initial TTL value, and it is decreased by one each time the packet is processed by the router.
• Protocol - Field is used to identify the next level protocol.  This 8-bit binary value indicates the data payload type that the packet is carrying.
• Source IPv4 - Contains a 32-bit binary value that represents the source IPv4 address of the packet.
• Destination IPv4 - Contains a 32-bit binary value that represents the destination IPv4 address of the packet.

IPv6 - 

• Version - This field contains a 4-bit binary value set to 0110 that identifies this as an IPv6 packet.
• Traffic Class - This 8-bit field is the equivalent to the IPv4 DS field.
• Flow Label - This 20-bit field suggests that all packets with the same flow label receive the same type of handling by routers.
• Payload Length - This 16-bit field indicates the length of the data portion or payload of the IPv6 packet.
• Next Header - This 8-bit field is equivalent to the IPv4 Protocol field.  It indicates the data payload type that the packet is carrying.
• Hop Limit - This 8-bit field replaces the IPv4 TTL field and is decremented by a value of 1 by each router that forwards the packet.
• Source IPv6 Address - This 128-bit field identifies the IPv6 address of the sending host.
• Destination IPv6 Address - This 128-bit field identifies the IPv6 address of the receiving host.

How does a host device use routing tables to direct packets to itself, a local destination, or a default gateway?

A host can send a packet to:

• Itself - A host can ping itself by sending a packet to a special IPv4 address of 127.0.0.1, which is referred to as the loopback interface. Pinging the loopback interface tests the TCP/IP protocol stack on the host.
• Local Host - This is a host on the same local network as the sending host. THe hosts share the same network address.
• Rremote Host - This is a host on a remote network. The hsots do not share the same network address.
• Default Gateway - A host's routing table will typically include a default gateway. The host receives the IPv4 address of the default gateway either from DHCP or statically.

What are the similarities and differences between host routing tables and routing tables of routers?  

Host routing tables display three sections related to the current TCP/IP network connections:

• Interface List - Lists the MAC address and assigned interface number of every network-capable interface on the host.
• IPv4/IPv6 Route Tables - Lists all known IPv4/IPv6 routes, including direct connections, local network, and local default routes.

Router routing tables provide routing information for directly-connected networks and remote networks and has information on how the route was learned, the trustworthiness and rating of the route, when the route was last updated, and which interface to use to reach the requested destination.

What are the common components and interfaces of a router?

Common components of a router include: the Central Processing Unit (CPU), Operating Systems (OS), and memory consisting of random-access memory (RAM), read-only memory (ROM), nonvolatile random-access memory (NVRAM), and flash.

Common router interfaces include:

• Console - A physical management port that provides out-of-band access to a Cisco device.
• Secure Shell (SSH) - A method for remotely establishing a secure CLI connection through a virtual interface, over a
  network.
• Telnet - An insecure method of remotely establishing a CLI session through a virtual interface, over a network.

What are the steps in the bootup process of a Cisco IOS router?

There are three major phases to the bootup process:

1. Perform the POST and load the bootstrap program;
2. Locate and load the Cisco IOS software; and
3. Locate and load the startup configuration file or enter setup mode.

Router(config)# interface fastethernet (#/#)

or

Router(config)# interface gigabitethernet (#/#)

How do you configure the default gateway on network devices?

Commands to Configure a Switch Default Gateway:

Enter global configuration mode:                            S1# configure terminal

Configure the switch default gateway:                    S1(config)# ip default-gateway 172.17.99.1

Return to privileged EXEC mode:                            S1(config)# end

Save the running config to the startup config:        S1# copy running-config startup-config

Which field in a router's routing table identifies an IP address of the next router to forward packet?

How do routers know where to forward packets?

What is the table that is used by router to forward the data?

Which command will show the IP routing table of a router?