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Week 2: Network Fundamentals (Network Topologies / Architectures and…
Week 2: Network Fundamentals
Network Topologies / Architectures
and Representation
Topology
Logical Topology
The way a network transfers frames from one node to the next. This arrangement consists of virtual connections between the nodes of a network. These logical signal paths are defined by data link layer protocols.
The logical topology of point-to-point links is relatively simple, while shared media offers different access control methods
Physical Topology
Physical connections and identifies how end devices and infrastructures devices such as routers, switches, and wireless access points interconnected
WANS
Point-to-point
This is the simplest topology. It consists of a permanent link between two endpoints. For this reason, this is a very popular WAN topology.
Hub and Spoke
A WAN version of the star topology in which a central site interconnects branch sites using point-to-point links.
Mesh
This topology provides high availability, but requires that every end system be interconnected to every other system. Therefore, the administrative and physical costs can be significant. Each link is essentially a point-to-point link to the other node.
LANs
Star
End devices are connected to a central intermediate device. Early star topologies interconnected end devices using Ethernet hubs.
However, star topologies now use Ethernet switches. The star topology is easy to install, very scalable (easy to add and remove end devices), and easy to troubleshoot.
Extended Star
In an extended star topology, additional Ethernet switches interconnect other star topologies. An extended star is an example of a hybrid topology.
Bus
All end systems are chained to each other and terminated in some form on each end. Infrastructure devices such as switches are not required to interconnect the end devices. Bus topologies using coaxial cables were used in legacy Ethernet networks because it was inexpensive and easy to set up.
Ring
End systems are connected to their respective neighbors, forming a ring. Unlike the bus topology, the ring does not need to be terminated. Ring topologies were used in legacy Fiber Distributed Data Interface (FDDI) and Token Ring networks.
IPv4 Network Addresses
IPv4 Addresses
Binary numbering system consists of numbers 0 and 1 (bits)
IPv4 addresses are expressed in 32 binary bits divided into 4 8-bit octets
IPv4 addresses are commonly expressed in dotted decimal notation
Binary to Decimal Conversion
To convert a binary IPv4 address to decimal, enter the 8-but binary number of each octet under the positional value of row 1 and then calculate to produce the decimal.
To convert a decimal IPv4 address to binary, use the positional chart and check first if the number is greater than the 128 bit. If no, a 0 is placed in this position; If yes, then a 1 is placed in this position.
128 is subtracted from the original number and the remainder is then checked against the next position (64). If it is less than 64, a 0 is placed in this position. If it is greater, a 1 is placed in this position and 64 is subtracted. The process repeats until all positional values have been entered.
Network and Hosts
Can be identified with
Subnet Mask
Compared to address bit for bit
Prefix Length
no. of bits in subnet mask set to 1
Logical AND
A logical AND is one of three basic binary operations used in digital logic
Used to determine the Network Address
The Logical AND of two bits yields the following results:
0 AND 1 = 0
0 AND 0 = 0
1 AND 1 = 1
1 AND 0 = 0
Network, Host and Broadcast Addresses
Types of Addresses in Netowrk 192.168.10.0/24
First Host address - host portion is all 0s and ends with a 1 (.0000001)
Last Host address - host portion is all 1s and ends with a 0 (.11111110)
Network Address - host portion is all 0s (.00000000)
Broadcast Address - host portion is all 1s (.11111111)
IPv4 Unicast, Broadcast and Multicast
Static IPv4 Address Assignment to a Host
Some devices like printers, servers and network devices require a fixed IP address
Hosts in a small network can also be configured with static addresses
Dynamic IPv4 Address Assignment to a Host
Most networks use Dynamic Host Configuration Protocol (DHCP) to assign IPv4 addresses dynamically
The DHCP server provides an IPv4 address, subnet mask, default gateway and other configuration information
DHCP leases the addresses to hosts for a certain length of time
If the host is powered down or taken off the network, the address is returned to the pool for reuse
Communication
Unicast
One-to-one comms
Use address of desti. device as desti. address
Broadcast
One-to-all comms
Message sent to all devices in same LAN
Multicast
Sending packet from host - selected group of subscribers
IOS Bootcamp
Access Methods
Secure Shell(SSH)
inband method for remotely and securely establishing a CLI session over a network. User authentication, passwords, and commands sent over the network are encrypted. As best practice, use SSH instead of Telnet whenever possible.
Telnet
Inband interfaces remotely establishing a CLI session through a virtual interface, over a network.
Console Port
Out-of-band serial port used primarily for management purposes such as the initial configuration of the router.
Network Infrastructure
Types of infrastructure
Network components
Devices
Media
Services
Three layer LAN model
Access Layer
Distribution Layer
Core Layer