Lesson 4: FUNDAMENTALS OF IPv4 Addressing and Routing

ping

An Internet Control Message Protocol (ICMP) echo message and its reply; ping often is used in IP networks to test the reachability of a network device.

subnets

are subdivided class A,B, or C networks that prevent wasting of IP addresses.

Subnetting

defines methods of IPv4 address space into smaller groups

Routing Protocol

1. Dynamically learn and fill a routing table with routes to each subnet. 2. Place the best route in the routing table whenever more than one route is available to a subnet. 3 Remove routes that are no longer available or valid. 4 Quickly find a replacement route for a lost route. 5. Prevent the creation of routing loops.

router forwarding logic

1. Ensure that the frame had no errors and if errors are found, discard the frame . 2. Discard the old data-link header and trailer, leaving only the IP packet in the frame. 3. Compare the IP packet's destination IP address to the routing table. 4. Find the best route to the destination address, which identifies the router's outgoing interface. 5. Encapsulate the packet inside a new data-link header and trailer, which is appropriate for the outgoing interface. 6. Forward the frame to the destination.

IP network

An IPv4 Class A, B, or C network; called a classful network because these networks are defined by the class rules for IPv4 addressing.

routing table

A list of routes in a router, with each route listing the destination subnet and mask, the router interface out which to forward packets destined to that subnet, and as needed, the next-hop router's IP address.

ARP (network layer)

A method through which MAC address of another device on a network can be obtained

DNS (network layer)

A naming system that identifies computers using hostnames

routing protocol

A set of messages and processes with which routers can exchange information about routes to reach subnets in a particular network. Examples of routing protocols include the Enhanced Interior Gateway Routing Protocol (EIGRP), the Open Shortest Path First (OSPF) protocol, and the Routing Information Protocol (RIP).

Ping (network layer)

A test that uses ICMP echo and reply to check network connectivity

ARP

Address Resolution Protocol. An Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.

unicast IP address

An IP address that represents a single interface. In IPv4, these addresses come from the Class A, B, and C ranges.

IP packet

An IP header, followed by the data encapsulated after the IP header, but specifically not including any headers and trailers for layers below the network layer.

DNS

Domain Name System. An application layer protocol used throughout the Internet for translating host names into their associated IP addresses.

default gateway/default router

On an IP host, the IP address of some router to which the host sends packets when the packet's destination address is on a subnet other than the local subnet.

IPv4 Header

Row 1: Version, Length, DS Field, Packet Length Row 2: Identification, Flags, Fragment Offset Row 3: Time to Live, Protocol, Header Checksum Row 4: Source IP Address Row 5: Destination IP Address

IP subnet

Subdivisions of a Class A, B, or C network, as configured by a network administrator. Subnets allow a single Class A, B, or C network to be used instead of multiple networks, and still allow for a large number of groups of IP addresses, as is required for efficient IP routing.

hostname

The alphanumeric name of an IP host.

dotted decimal notation (DDN)

The format used for IP version 4 addresses, in which four decimal values are used, seperated by periods (dots).

IPv4 address exhaustion

The process by which the public IPv4 addresses, available to create the Internet, were consumed through the 1980s until today, with the expectation that eventually the world would run out of available IPv4 addresses.

subnetting

The process of subdividing a Class A, B, or C network into smaller groups called subnets.