CSIS 4823 Data Communications Networking - Networking Review Mr. Mark Welton
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