CSIS 4823Data Communications

Networking - Networking Review

Mr. Mark Welton

What is a Network?

A computer network, or simply a network, is a collection of computers and other hardware interconnected by communication channels that allow sharing of resources and information. Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. A network is a group of devices connected to each other. Networks may be classified into a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, benefit, and organizational scope. - Wikipedia

A computer network can be defined as two or more computers connected by some means through which they are capable of sharing information

So is sneaker net a network?

A connection involves some sort of addressing or identification of the nodes on the network, allowing them to speak the same protocol or language.

Network Have Connections

Types of networks: LAN - is a network that is confined to a limited

space, such as a building or floor. WAN - A WAN is a network that is used to

connect LANs by way of a third-party provider. CAN - is a network that connects LANs and/or

buildings in a discrete area owned or controlled by a single entity. MAN - is a network that connects LANs and/or

buildings in an area that is often larger than a campus.

What is in a name?

We also describe networks by the technology they use◦ Ethernet◦ Token Ring◦ FDDI (Fiber Distributed Data Interface)

Or the Protocols:◦ ATM◦ Frame Relay◦ MPLS◦ T1◦ DS3

Or the layer:◦ Bridged◦ Routed◦ Point-to-point

What is in a name?

Early Ethernet, 10Base-5 used a thick cable named thick-net

10Base-2 Ethernet replaced 10Base-5 and used a smaller coaxial cable named thin-net

Both used either an N or BNC connector to couple cables together and required terminators to be installed at the end of a cable run

These cable runs formed the physical backbone of Ethernet networks

Early Networks

Ethernet running over UTP cables terminated with RJ45 connectors made use of hubs

Hubs became the new backbone of many installations

As hubs became less expensive, extra hubs were often used a repeaters in more complex networks

Hubs are layer one devices (physical/electrical devices) and do not alter frames or make decisions on traffic it sees

Early Networks

A hub is simply a means of connecting Ethernet cables together so that their signals can be repeated to every other connected cable on the hub

Hubs may also be called repeaters for this reason, but it is important to understand that while a hub is a repeater, a repeater is not necessarily a hub.

Hubs and Repeaters

If another device is already using the wire, the sending device will wait a bit and then try to transmit again

When two stations transmit at the same time, a collision occurs

Each station records the collision, backs off again, and then retransmits

A collision domain is an area of an Ethernet network where collisions can

occur

Collision

A broadcast domain is the area of an Ethernet network where a broadcast will be propagated

Broadcasts stay within a Layer-3 network (unless forwarded), which is usually bordered by a Layer-3 device such as a router

A broadcast storm results in the attempt to build redundancy into the network

The only way to resolve a broadcast storm is to break the loop

Broadcast Domain

Broadcast Storm

The 5-4-3 rule of Ethernet design states that between any two nodes on an Ethernet network, there can be only five segments, connected via four repeaters, and only three of the segments can be populated. This rule, which seems odd in the context of today’s networks, was the source of much pain for those who didn’t understand it.

5-4-3 Rule

5-4-3 Rule

Switches differ from hubs by playing an active role in the processing of frames on the network

Switch - The general term used for anything that can switch

Ethernet Switch - Any device that forwards frames based on their Layer-2 MAC addresses using Ethernet

A switch creates a collision domain on each port, while a hub’s collision domain exists on all ports

Switches

Layer-3 Switch - This is a switch with routing capabilities

Multilayer Switch - Similar to a Layer-3 switch, but may also allow for control based on higher layers in packets. Multilayer switches allow for control based on TCP, UDP, and even details contained within the data payload of a packet

Switching - is the act of forwarding frames based on their destination MAC addresses

Switches

Every frame contains the source and destination MAC address switch inspects the frame to determine the source MAC address and

adds the address into its address table The switch then determines the frame’s destination MAC address and

checks the table If a match exists, the frame is forwarded from the source port to the

destination port. If no match is found, the frame is sent to all ports

Routing - refers to determining the path for something

For IP, packets and frames are forwarded by switches and hubs

To reach a destination, not on the local network, the packet must be forwarded to a gateway

The gateway (router) is responsible for determining how to get the packet to where it needs to go

Routing

Routers communicate with each other by routing protocols

These protocols let the routers learn information about other networks which are stored in the routing table of the router

With the introduction of layer three switches – routers tend to remain WAN-focused, while switches remain LAN-focused

Routing

Routing is a fundamental process common to almost every network

Each routing protocol has its own table of information (learned through its own protocol – in addition to the routing table of the router)

Metrics - the values or weight used by a routing protocol to determine its best path to a destination

Administrative distance is the values assigned to each routing protocol by the router in order to prioritize learned routes

Routing

If the same route is learned from two sources within a single routing protocol, the one with the best metric will win

If the same route be learned from two routing protocols within a single router, the protocol with the lowest administrative distance will be preferred

Routing

When a packet arrives at a router, the router determines whether the packet needs to be forwarded to another network

If it does, the router checks the routing table to determine if it contains a route to the destination network

If there is a match, the packet is forwarded out the proper interface to where it belongs

If there is no match found in the routing table, the packet is forwarded to the default gateway, if one exists, or dropped if no default gateway exists

Routing

IP destination networks are often described by a network address and prefix length

The prefix length is the number of bits set to 1 in the subnet mask

Networks are described in the format network-address/prefix-length

i.e. 10.0.0.0/16 referred to as a prefix

Routing

10.0.0.0/24 10.0.0.0/16 10.0.0.0/8 Which has the longer prefix? A longer prefix means a more specific

match to a destination

Host route subnet route summary route major network route supernet route default route

Types of Routes

Host route is a route to a host (node), not a network

Host routes have a subnet mask of 255.255.255.255 or a /32 prefix

The subnet mask is all 1s

Host Route

Subnet route is a portion of a major network The subnet mask is used to determine the

network 24 is a subnet of the classful 10.0.0.0

network Subnets make use of Variable Length

Subnet Masks of classful major networks

Subnet Route

Summary route is a single route that references a group of subnets

10.1.0.0/16 would be a summary route for the subnet routes of 10.1.1.0/24 and 10.1.2.0/24

Summary Route

is any classful network with its traditional subnet mask

Class A, B, C networks

Major Route

Supernet route is a single route that references a group of major network

192.168.0.0.0/15 is a supernet for 192.168.0.0.0/16 and 192.169.0.0/16

Supernet route

Default route is the gateway (route) of last resort

typically shown as 0.0.0.0 (an all zero) destination

The subnet mask is all zeroes

Default Route