What is a Collision Domain?

A computer network can be segmented physically but also logically. A collision domain is one of the logical network segments in which the data packets can collide to each other. One of the most common protocols used when referring to a collision domain is the Ethernet protocol. Collision domains are often referred as 'Ethernet segments'.

The term of 'collision domain' is also used when describing the circumstances in which a single network device sends packets throughout a network segment and forces every other device in that network segment to pay attention to those packets.

CSMA/CD and Collision Domains

A collision domain can also be a group of Ethernet/Fast Ethernet devices in a Local Area Network running on the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) feature and being connected through repeaters, thus competing for network access. Since only one device in the same collision domain can transmit data at a certain point, the other devices in the network simply listen in order to avoid data collisions.

CSMA/CD is a set of rules telling each network devic-e when to transmit and when to stop transmitting data. When someone in the network wants to transmit something, it "listens" to the network at first in order to see if anyone else is using the channel. If no one else is transmitting, the device will go forward with its own transmission.

The usage of CSMA/CD is an efficient way of avoiding network collisions, but it's not foolproof. It's obvious that if two devices follow the exact same procedure at the exact same time, their transmissions will 100% collide, and they will both become unusable. A jam signal will be sent in order to let everyone else know that a collision took place and they should not send any data. The hosts that collided will each start a random timer, and when that ends, each host will begin to listen on the network again.

Of course, the more collisions in a network, the less efficient the network is.

'Collision domain' sometimes reffers to a system where a unique identifier is open for multiple interpretations over different layers. The analogy to our ethernet collision domain is very clear if not obvious.

A collision occurs when two or more network devices are trying to transmit packets at the exact same time.

How to reduce the size of the collision domain?

Reducing the collision domain size can be the result of installing network devices (usually switches and/or network bridges) that use microsegmentation.

Unlike network hubs and regular repeaters that usually broadcast every single packet, LAN switches are able to filter and forward packets by their MAC address (Media Access Control). The switch basically reads the 48-bit MAC address from the network card and is able to filter or stop frames inside the LAN or a certain network domain.

A switch or network bridge will forward frames with addresses that are not in its domain, and will duplicate and broadcast frames to the devices inside its network.

A router can also filter, forward or drop packets based on the MAC addresses, but it can also act based on the Internet Protocol (IP). Routers also act on reducing the collision domain by broadcasting to the LAN only packets that have addresses on that certain network. These network devices are able to route or redirect packets not only by the IP or MAC addresses, but also by the data type (email, graphics, plain text), function or port used (FTP, HTTP, SMTP, POP3) and other variables and functions (acting like a firewall) in order to improve the performance and also reduce the number of collisions and control/limit users.

What is a Broadcast Domain?

Definitions of a Broadcast Domain

A broadcast domain is a logical part of a network (a network segment) in which any network equipment can transmit data directly to another equipment or device without going through a routing device (assuming the devices share the same subnet and use the same gateway; also, they must be in the same VLAN).

A more specific definition of the broadcast domain is that certain area of the computer network that's composed by every single computer or network equipment that can be reached directly by sending a simple frame to the data link layer's broadcast address.

Details on Broadcast Domains

While any layer 2 device is able to divide the collision domains, broadcast domains are only divided by layer 3 network devices such as routers or layer 3 switches.

Frames are normally addressed to a specific destination device on the network. While all devices detect the frame transmission on the network, only the device to which the frame is addressed actually receives it. A special broadcast address consisting of all 1s is used to send frames to all devices on the network.

The VLAN (Virtual Local Area Network) technology can also create a so-called "virtual" broadcast domain. A network built with switching devices could see each network devices as an independent system. These groups of independent systems can be joined into one broadcast domain, even if the computers are not physically connected to each other. This is very useful when administrating large networks where there's the need for better network management and control.

How to restrict the broadcast domain?

Since a broadcast domain is the area where broadcasts can be received, broadcasts are restricted by routers. If a router receives a broadcast signal, it simply drops it. In other words, the edge or border router connected to the Internet will not up-broadcast or will not relay that broadcast message. This is problematic and not foolproof either. Supposing two networks exist and they're connected to each other through a router. The first network has a running DHCP server that offers IP addresses to networked systems. On the other side, there is no valid DHCP server running on the second network. Offering IP addresses from the first network's DHCP server to the second network's systems can be a difficult task to accomplish since DHCP is a broadcast, and the router that joins the networks drops the broadcast traffic. This leaves any DHCP request in the second network, unanswered. Many router manufacturers provide capabilities for DHCP forwarding to solve this problem. This can be bypassed by connecting the two networks with a well configured, Linux-based, purpose-oriented software router. That will handle the job properly and without further issues.

Examples of Broadcast Domain Implementation

A broadcast domain can be perceived as a portion of a network that is reachable by network broadcast (an address resolution request of some sort of an announcement of availability. Messages like "Can I have the address of that network node?" or "I'm here, a part of this network". Again, unlike collision domains, broadcast domains can be started at several protocol layers, therefore the broadcast domain as a whole can be within a single LAN segment but it can be routed over other segments as well.

What is IP?

IP (Internet Protocol) is the main network layer protocol utilized on the Internet.

P is responsible for addressing and fragmentation.

IP works with another network layer protocol, ICMP.

Transport layer protocols which utilize IP include TCP and UDP.

IP Addresses

IP addresses are four octets (32 bits) long and are usually seperated by periods. Some example IP addresses are:

• 127.0.0.1
• 10.0.0.1
• 38.250.25.1

IP addresses are using in routing packets through the Internet.

Diagram of the IP Header

                        IP Header Format
                       -----------------
                                  
   0                   1                   2                   3  
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Version|  IHL  |Type of Service|          Total Length         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Identification        |Flags|      Fragment Offset    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  Time to Live |    Protocol   |         Header Checksum       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Source Address                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Destination Address                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Options                    |    Padding    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IP Versions

The version of IP in current use is IPv4. IPv6 has been defined, but is not yet in common use.

Additional Reading on IP

The IP protocol is defined in RFC 791: Internet Protocol.

What is 127.0.0.1?

127.0.0.1 is the standard IP address used for a loopback network connection.

This means that if you try to connect to 127.0.0.1, you are immediately looped back to your own machine.

What is a Broadcast Address?

A broadcast address is an IP address that you can you to target all systems on a specific subnet instead of single hosts. The broadcast address of any IP address can be calculated by taking the bit compliment of the subnet mask, sometimes referred to as the reverse mask, and then applying it with a bitwise OR calculation to the IP address in question.

Some systems which are derived from BSD use zeros-broadcasts instead of ones-broadcasts. This means that when you create a broadcast address, you fill the host area of the IP address while displayed using binary values with zeros instead of ones. Most operating systems use ones-broadcasts. Changing systems to use zeros-broadcasts will break some communications in the wrong environments, so understand your needs before changing your broadcast address or its type.

Math example

If you have a system with IP address 192.168.12.220 and a network mask of 255.255.255.128, what should the broadcast address for the system be? Remember, to do this calculation, you need to convert all numbers to binary values. For bitwise OR, remember that any two values where at least one value is "1", the result will be "1", otherwise the result is "0".

IP Address:	11000000.10101000.00001100.11011100
Reverse Mask:	00000000.00000000.00000000.01111111
bitwise OR:	-----------------------------------------------
Broadcast:	11000000.10101000.00001100.11111111

Convert the binary value back to octal, and you have your resulting value of 192.168.12.255. You can use the tech-faq.com subnet calculator to assist you in calculating network IP address values.

Setting up a broadcast address

In most cases the broadcast address will be properly set up by modern operating system once you enter the IP address and subnet mask. In some older unix systems that use classful definitions of subnets, the broadcast address is improperly formed, and you will need to change it.

Changing windows systems broadcast addresses

Windows systems do not allow you to change the broadcast address by hand. You can, however, choose whether the system uses zeros-broadcasts or ones-broadcasts. To change a windows system to use zeros-broadcasts, use the following procedure:

• Log into the windows system with an account with administrator rights.
• Open your registry editor. If you are not knowledgable in using the registry editor for windows, please do not perform these steps. A mistake can make your system unusable.
• Find the registry key "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ Tcpip\Parameters\Interfaces\[Adapter ID]". Replace [Adapter ID] with the actual adapter ID you want to change the broadcast address for. You can get a list of all the adapter IDs in your windows system by opening a command line prompt, and executing a "ipconfig /all" command.
• Create a new DWORD value called "UseZeroBroadcast". Set its inital value to "1". You can use a hex or binary value in this case, since 1 is the same for both numbering systems.
• Reboot your system for the changes to take effect.
You have enabled zeros-broadcast for that adapter.

Changing unix systems broadcast addresses

Unix systems give the administrator a method to change the broadcast address to whatever value that they see fit to change it to. Ensure you know what you are doing before changing your broadcast address. In some cases, when using ifconfig from the command line, the broadcase address gets set to a classful based broadcast instead of the proper broadcast. You can check your results using the "ifconfig" command. Unfortunately, every unix system has differing syntax for the ifconfig command, and not all command options are available for every unix system. Check your ifconfig man page if you get hung up. The sample procedure below is the process you would use on a linux system to change a system broadcast address.

• Open a terminal window, telnet, or ssh into the unix system in question, and log into the system.
• "Su" or "sudo" commands properly to get root priviledges.
• Determine which adapter you want to change the broadcast address on the system by checking the output of "ifconfig -a".
• Execute "ifconfig broadcast ". Replace and with the proper values.
• Test your configuration.

VLSM

VLSM - A Very Brief History

You read in the subnetting section that we were about to run out of IP addresses. One way to preserve IP addresses was to allocate certain ranges of IP address which can be used for free on your network so long as you don't use them to get out to the internet. If you want to get out to the internet using them then your router can just swap it for a routable address using a technique called Network Address Translation (NAT).

Free addresses to use are:

10.0.0.0 - anything starting with a 10

172.16.0.0 to 172.31.0.0 - inclusive

192.168.0.0 - any address starting with these two numbers

Using VLSM

Say you are using the following number:

192.168.1.0 which if you have read the subnetting section you know lets you use 254 hosts on your network. If you only have 20 hosts on your network it means you have wasted 204 addresses. Now imagine if you are paying for each block of addresses, you are going to waste a huge amount of money as well.

VLSM lets you cut your network into smaller chunks which are called subnets. All you have to do it add some numbers to the end of your subnet mask and your network will see that you are subnetting it down. Please see the easy way to subnet section for more information on how to actually do it.

How VLSM Works

If you change your subnet mask from 192.168.1.0 255.255.255.0 to 255.255.255.224 your network device will see the change and let you break down your network into smaller parts. That actual number tells the network to chunk your network down into subnet blocks of 32. If you use the subnetting cheat chart you will see how this actually works.

The subnet mask 255.255.255.224 gives you 8 subnets with 32 available addresses. Each subnet must start with a subnet number and end with a broadcast number so technically that leaves you with 30 host addresses per subnet. This is still plenty if you only needed 20 per subnet.

We have gone from one subnet with 255 addresses:

To 8 subnets with 32 IP addresses per subnet.

A RFC (request for comment) was submitted which suggested that we could allocate numbers to hosts on networks instead of hostnames. The current implementation of this scheme is IP version 4 although IPv6 is now replacing this.

The idea is that every address would be made up from four groups of eight binary numbers. Each group of eight binary numbers is known as an octet. Because we struggle to write numbers out in binary we usually convert them into decimal but computers and network devices still see all numbers in binary because they can only recognise on and off signals so either a 0 or a 1.

Binary Math 101

Binary maths - what you need to know in order to subnet

Here is a Secret

Technically you can get away with not knowing binary mathematics if you want to just be able to subnet your network. So long as you understand that all IP addresses are in binary and that each octet can only go from 0 to 255 then you should be fine. If you have any IT exams coming up, especially Cisco or Microsoft then you may well be asked to work out binary numbers and convert them to decimal or even hex!

How Binary Works

We use the decimal counting system as humans because we have ten digits on our hands so that is how mankind learned to count. Computers only have electrical currents so they can only see a current or no current. No current is 0 and current is 1. The only numbering system that can cater for this is binary.

Binary numbering starts with a 1 and then doubles in columns. You can count from 0 to infinity and beyond with this numbering system. Just keep adding columns (from right to left). A 0 means don't use that number and a 1 means do use that number.

Numbers	2	1
Binary	1	0

Here you have a1 or 'on' number in the 2 column and a 0 or 'off' in the 1 column so your number is 0.

Numbers	4	2	1
Binary	1	0	1

This time we have a 1 in the 1 and the 4 columns so we simply add that together to get 5 as the answer.

Numbers	8	4	2	1
Binary	1	1	0	1

And this time we have a 1 in the 8,4 and 1 columns so adding them together we have 13.

We could keep going here but we should stop at 8 columns because current IP addresses use eight binary places or an octet. In fact an IP version 4 address uses 4 octets.

Numbers	128	64	32	16	8	4	2	1
Binary	1	0	0	1	1	1	0	1

In the above example we add 128+16+8+4+1 to get 157.

An IP address in binary would look like this to a computer or router:

11010010.11101101.11000010.11110110 which is four octets.

Convert Binary to Decimal

This is a very simple process. Just write out the binary number putting it into the above chart. Add the numbers together and you have your answer.

Convert Decimal to Binary

A little more tricky. Write out the above chart again and put a 1 in the numbers which add up to your required binary number. So if you wanted to work out 203 in binary you would tick the 128 and 64 columns (192), ticking the 32 column would give it too much, tick the 8 column (200) and then the 2 and 1 columns. If you prefer you can start from the other end adding 1 to 2 to 4 and so on but it does work better from the left to right.

Your answer would look like this:

Numbers	128	64	32	16	8	4	2	1
Binary	1	1	0	0	1	0	1	1

Class C Subnetting

You can recognise a Class C address because the first octet is a number from 192 to 223 inclusive. So any of the below IP addresses are Class C.

192.1.2.4

200.2.3.5

223.1.2.3

Network devices recognise a Class C address as such because the numbers are checked in binary and the first number in the first octet always begins with the binary number 110. Check the binary section for more info on that.

Class C addresses lock the first three octets for network numbers. The remaining three octets can be used for host numbers. It works like this:

Network	Network	Network	Host
223	23	2	4

In the above example 223.23.2 is the network number and .4 is a host on that network.

Please note that Class A, B and C addresses are only called such for historical purposes now and you may find that your company could be allocated a Class A address or even one for your home IP address for your broadband connection. VLSM means that we don't have to concern ourselves with Classes of address anymore.

Class B Subnetting

You can recognise a Class B address because the first octet is a number from 128 to 191 inclusive. So any of the below IP addresses are class B.

128.1.2.4

177.2.3.5

191.1.2.3

Network devices recognise a Class B address as such because the numbers are checked in binary and the first number in the first octet always begins with the binary number 10. Check the binary section for more info on that.

Class B addresses lock the first two octets for network numbers. The remaining three octets can be used for host numbers. It works like this:

Network	Network	Host	Host
129	23	2	4

In the above example 129.23 is the network number and 2.4 is a host on that network.

Please note that Class A, B and C addresses are only called such for historical purposes now and you may find that your company could be allocated a Class A address or even one for your home IP address for your broadband connection. VLSM means that we don't have to concern ourselves with Classes of address anymore.

Class A Subnetting

All IP addresses were divided into classes when they were first devised. The idea was that Class A addresses were allocated to large companies. Class B to medium sized companies and Class C to any other company who needed an IP address. Class D is for multicasting such as streaming media and Class E is reserved for experimental use.

You can recognise a Class A address because the first octet is a number from 1 to 126 inclusive. So any of the below IP addresses are class A.

10.1.2.4

120.2.3.5

125.1.2.3

Network devices recognise a Class A address as such because the numbers are checked in binary and the first number in the first octet always begins with the number 0. Check the binary section for more info on that.

Class A addresses lock the first octet for network numbers. The remaining three octets can be used for host numbers. It works like this:

Network	Host	Host	Host
20	23	2	4

In the above example 20 is the network number and 23.2.4 is a host on that network.

Please note that Class A, B and C addresses are only called such for historical purposes now and you may find that your company could be allocated a Class A address or even one for your home IP address for your broadband connection. VLSM means that we don't have to concern ourselves with Classes of address anymore.

Subnet Zero

Subnet Zero

IP subnet zero questions seem to pop up on various network discussion groups every few days. Some people are not clear about what it is and how it will affect them in interviews and exams.

What is Subnet Zero?

When you are calculating subnet masks the result of your calculations generates various subnets. Each subnet starts with a number so if you use the example in easy way to subnet you will see that your subnet addresses are:

192.168.1.0

192.168.1.64

192.168.1.128

192.168.1.192

Subnet zero is the subnet which has all binary 0's in the address. So for the number 192.168.1.0 you have in the last octet eight zeros for the subnet number or 00000000. The last octet has all 1's in the subnet part. Please re-read the easy way to subnet section again but remember that we are stealing three bits from the last octet to make a subnet. If you write out the address 192 for the last subnet above you would see that the first three bits of the last octet are binary 1's or 11100000.

The same actually goes for the first subnet. I know I said that there were eight binary 0's in it but only the first three count for the subnet, the last five are for the hosts on that subnet. If subnet zero is not allowed you will always lose two subnets so in the below example if your subnet mask is 255.255.255.224:

192.168.1.0 - You can't use this subnet as it is all 0's in the subnet

192.168.1.64

192.168.1.128

192.168.1.192 - You can use this subnet as it is all 1's in the subnet

If you can use subnet zero you get this:

192.168.1.0 - You can use this subnet

192.168.1.64 - You can use this subnet

192.168.1.128 - You can use this subnet

192.168.1.192 - You can use this subnet

So Can You Use Subnet Zero?

The answer is 'yes you can.' Unless you are told otherwise you should presume that subnet zero is always allowed. In an IT exam it will usually tell you if you are not permitted to use it but to prevent it's use is a bit old fashioned.

Easy Way to Subnet

Easy Way to Subnet

Learn the easy way to subnet using the proven Subnetting Secrets™ method.

Step 1

Write out the subnetting cheat chart by hand. You need to be able to do it by hand in case you have to work out subnetting problems in your head or in an exam. The subnetting cheat chart is here.

Step 2

Look at the IP address and subnet mask. If the subnet mask is written out in abbreviated form (called CIDR) then just count up in blocks of eight and add the last few numbers to reach the subnet mask. e.g.

192.168.1.23/26 - we need to work out what the slash 26 actually is when written out as a full subnet. The binary maths section tells you that 255 in binary is equal to 8 and we need to reach 26 so..

255 is 8 255.255 is 16 bits 255.255.255 is 24 bits and to get to 26 we need to add 2 to 24 so tick two places down on the top left column on the subnetting cheat chart.

128
192
224
240
248
252
254
255

So you can see that by ticking down two (which is 24 + 2 = 26 bits) we have generated the subnet mask of 255.255.255.192 which if write out in binary bits is 26 binary bits (or 8 + 8 + 8 + 2).

Step 3

Tick the same number across the top row of the Subnetting Secrets Cheat Chart.

128	64	32	16	8	4	2	1

The above table is purely one binary octet written out in decimal. Whichever number your last tick ends at tells you which number your subnets begin on. Don't worry if this doesn't make much sense at the moment. Please keep with it and like any new still, it will click very soon.

So we have it number 64 which tell us that our subnets are going up in increments of 64. Our host number out of the IP address 192.168.1.23 is the number 23. It is 23 because 192 is a traditional class C address so we can only use numbers in the last octet for IP addresses.

Let's write out our subnets counting up in increments of 64. We are allowed to start with IP subnet zero because the guys who invented the RFC (requests for comment) for subnetting designed it to permit that.

192.168.1.0 - this is the first subnet and is known as the zero subnet. Host number 23 is in here because if we go to the next subnet we have gone well past 23.

192.168.1.64 - we have added the first 64 to the end.

192.168.1.128 - we have added another 64 to the end. This is our 3rd subnet.

192.168.1.192 - our last subnet. We can't go higher because our subnet mask ends in 192.

The answer to the question 'which subnet is host 192.168.1.23 in is subnet 192.168.1.0

Step 4 (Optional)

We have actually reached the answer so in an interview or exam stop there. They may ask another question though. They may ask you to identify the first and last host and the broadcast addresses for your subnet. This step is very easy.

Take the subnet our host 192.168.1.23 is in. To get the first host just add one to the subnet 192.168.1.0 so the answer is 192.168.1.1.

To get the broadcast address just jump to the next subnet and subtract one. Remember that the boxes our number go in can only run from 0 up to 255. We are working in binary here and writing it out in decimal. This is where novice network engineers can get stuck. Just picture each box as a rolling set of numbers like an odometer in a car. It just rolls from 0 to 1 to 2 to 3 and so on until it reaches 255 and then it rolls back to 0.

Take one away from the second subnet 192.168.1.64 so the broadcast address for your first subnet is 192.168.1.63.

To get the last host address take one away from that number. The answer is 192.168.1.62.

This is what we are left with:

Subnet	1st Host	Last Host	Broadcast
192.168.1.0	192.168.1.1	192.168.1.62	192.168.1.63

Effects of Subnetting a Class C Network

Effects of Subnetting a Class C Network

Subnet Mask	CIDR	Net Bits	Host Bits	# of Nets	Hosts/Net	Total Hosts
255.255.255.0	/24	0	8	1	254	254
255.255.255.128	/25	1	7	0(2*)	126	0(254*)
255.255.255.192	/26	2	6	2(4*)	62	124(248*)
255.255.255.224	/27	3	5	6(8*)	30	180(240*)
255.255.255.240	/28	4	4	14(16*)	14	196(224*)
255.255.255.248	/29	5	3	30(32*)	6	180(192*)
255.255.255.252	/30	6	2	62(64*)	2	124(128*)
255.255.255.254	/31	7	1	126(128*)	0**	0(128**)
255.255.255.255	/32	8	0	254(256*)	1***	254(256*)

Network topologies

Network topologies are categorized into the following basic types=

• bus
• ring
• star
• tree
• mesh

Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Star Topology

Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.

Tree Topology

Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

introduction

Hello my name is Uzman Khan. i have done MCS , CCNA and CCAI. My field is Networking . i want to do all the Cisco's Certifications . i want to share networking concepts with all of you. Please help me to build my blog.






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