IMDAD HUSSAIN

Differences between Hub

Bridge

Switch

Router

HubA Hub is the simplest of these devices. In general, a hub is the central part of a wheel where the

spokes come together. Hubs cannot filter data so data packets are sent to all connected

devices/computers and do not have intelligence to find out best path for data packets. This leads to

inefficiencies and wastage.

As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for

connections to a local area network (for example, an Ethernet or a token ring), and a connection to a

line. Hubs are used on small networks where data transmission is not very high.

Bridge

In telecommunication networks, a bridge is a product that connects a local area network (LAN) to

another local area network that uses the same protocol. Having a single incoming and outgoing port

and filters traffic on the LAN by looking at the MAC address, bridge is more complex than hub. Bridge

looks at the destination of the packet before forwarding unlike a hub. It restricts transmission on other

LAN segment if destination is not found.

A bridge works at the data-link (physical network) level of a network, copying a data frame from one

network to the next network along the communications path.

Switch

A switch when compared to bridge has multiple ports. Switches can perform error checking before

forwarding data, which are very efficient by not forwarding packets that error-end out or forwarding

good packets selectively to correct devices only.

Switches can support both layer 2 (based on MAC Address) and layer 3 (Based on IP address)

depending on the type of switch. Usually large networks use switches instead of hubs to connect

computers within the same subnet.

RouterA router, like a switch forwards packets based on address. Usually, routers use the IP address to

forward packets, which allows the network to go across different protocols. Routers forward packets

based on software while a switch (Layer 3 for example) forwards using hardware called ASIC

(Application Specific Integrated Circuits). Routers support different WAN technologies but switches do

not.

Besides, wireless routers have access point built in. The most common home use for routers is to share

a broadband internet connection. As the router has a public IP address which is shared with the

network, when data comes through the router, it is forwarded to the correct computer.

the original material is referred from:

switch vs router hub bridge repeater wireless access point

More tips on switches or routers comparison at:

Cisco Switch Comparison-catalyst 2960 VS 3560 VS 3750 VS 4500 VS 6500

Stacking Cisco 2960-S VS Cisco 3750 Switches

Cisco 1941 VS 2901-Comparison Helps You Choose the Right RouterTagged with: Bridge, bridge vs router, bridge vs switch, difference between router and switch, hub, hub vs bridge, Hub vs Bridge vs Switch vs Router, Router, router vs switch, Switch

What’s the difference between a Crossover Cable and Straight-Through Cable?

So you’ve seen the terms crossover cable and straight-through cable in a Cisco CCNA or CompTIA certification book  and you want some clarification on the difference between these two types of Ethernet cable.

To understand what crossover cables and straight-through cables are – you first need to know a little about the wires inside them.

From there you will know why a network professional would use use one over the other.

It’s all about understanding how different devices on a network send and receive signals.

Straight-Through CableRunning through the inside of an Ethernet cable are eight wires.

The cable is terminated at each end with RJ45 connectors – each connector having eight pins. Each of the eight pins has a wire ‘crimped’ (connected) to it.

A straight-through cable, gets its name because each of its eight wires runs from one pin of the RJ45 connector, ‘straight-through’ to the same corresponding pin at the other end of the cable.

So the wire connected to pin 1 of an RJ45 connector also connects to pin 1 on its other RJ45 connector. The same goes for the remaining seven wires.

What is the defference between Cross Cable and Straight Cable

Now days, LAN card has intelligence, so that both cables can work.

They have a feature on lots of switches and hubs etc called "auto-mdix" or "auto mdi/mdix", that is the new thing where it doesn’t matter what kind of cable you use, it will

just auto detect the proper connection type no matter which cable you use.

The cable can be categorized as Cat 5, Cat 5e, and Cat 6 UTP cable. Cat 5 UTP cable can support 10/100 Mbps Ethernet network, whereas Cat 5e and Cat 6 UTP cable can

support Ethernet network running at 10/100/1000 Mbps. You might hear about Cat 3 UTP cable, it's not popular anymore since it can only support 10 Mbps Ethernet network.

Straight and crossover cable can be Cat3, Cat 5, Cat 5e or Cat 6 UTP cable, the only difference is each type will have different wire arrangement in the cable for serving

different purposes.

Ethernet network cables are straight and crossover cable. This Ethernet network cable is made of 4 pair high performance cable that consists of twisted pair conductors that

used for data transmission. Both end of cable is called RJ45 connector.

There are two types of network cables commonly used in PC networks - Straight-through and cross-over.

 

Straight Cable

Usually use straight cable to connect different type of devices. This type of cable will be used most of the time and can be used to:

1) Connect a computer to a switch/hub's normal port.

2) Connect a computer to a cable/DSL modem's LAN port.

3) Connect a router's WAN port to a cable/DSL modem's LAN port.

4) Connect a router's LAN port to a switch/hub's uplink port. (Normally used for expanding network)

5) Connect two switches/hubs with one of the switch/hub using an uplink port and the other one using normal port.

If you need to check how straight cable looks like, it's easy. Both sides (side A and side B) of cable have wire arrangement with same color.

Crossover Cable

Sometimes you will use crossover cable, it's usually used to connect same type of devices. A crossover cable can be used to:

1) Connect two computers directly.

2) Connect a router's LAN port to a switch/hub's normal port. (Normally used for expanding network)

3) Connect two switches/hubs by using normal port in both switches/hubs.

In you need to check how crossover cable looks like, both side (side A and side B) of cable have wire arrangement with following different color.

This cable (either straight cable or cross cable) has total 8 wires (or we can say lines), i.e. four twisted pairs (4x2=8) with different color codes. Right now just forget about

color codes. It doesn’t matter what color is given to the cable (but there is a standard).

In straight cable connectivity is like as follows

RJ451 Connected to RJ452

Pin1------------------------------------- Pin1

Pin2------------------------------------- Pin2

Pin3------------------------------------- Pin3

Pin4------------------------------------- Pin4

Pin5------------------------------------- Pin5

Pin6------------------------------------- Pin6

Pin7------------------------------------- Pin7

Pin8------------------------------------- Pin8

 

In cross cable connectivity is like as follows

RJ451 Connected to RJ452

Pin1------------------------------------- Pin3

Pin2------------------------------------- Pin6

Pin3------------------------------------- Pin1

Pin4------------------------------------- Pin4

Pin5------------------------------------- Pin5

Pin6------------------------------------- Pin2

Pin7------------------------------------- Pin7

Pin8------------------------------------- Pin8

Purpose of this cross cable is RX (receiving terminal) connects to TX (transmitting) of one pc to another PC and vice versa.

As we use two PCs (same devices), straight cable will connect TX to TX and RX to RX of two computers, so cross cable is required. If you use HUB or switch, then straight

cable will work because it has internal arrangement like cross cable. So note that use cross cable to connect two similar devices.

A straight cable will not work to connect two computers together.

Crossover used to connect to PCs directly together, also used for connecting networking devices together like Switch to Switch etc.

Straight cables connect two DIFFERENT types of devices. Whereas crossover cables connect two of the SAME type

Now do this (if possible): connect cross cable between switch and PC and see what happens..!

   Hub  Switch Router  Workstation

 Hub  Crossover  Crossover  Straight  Straight

 Switch  Crossover  Crossover  Straight  Straight

 Router  Straight  Straight  Crossover  Crossover

 Workstation  Straight  Straight  Crossover  Crossover

-----------------------------------------------------------------------------------------------

Communication between Switches and Workstations

When a workstation connects to a LAN, it transmits data independently of the other devices connected to the LAN media. The workstation simply transmits data frames from

a NIC to the network medium.

If desired, the workstation can be attached directly to another workstation by using a crossover cable. Crossover cables connect the following devices:

Workstation to workstation

Switch to switch

Switch to hub

Hub to hub

Router to router

Router to PC 

Straight-through cables connect the following devices:

Switch to router

Switch to workstation or server

Hub to workstation or server 

Many modern switches now automatically adjust the port pinout to support the particular cable attached, whether it is a crossover or straight-through cable.

Switches, which are Layer 2 devices, use intelligence to learn the MAC addresses of the devices that are attached to its ports. This data is entered into a switching table. After

the table is complete, the switch can read the destination MAC address of an incoming data frame on a port and immediately forward it. Until a device transmits, the switch

does not know its MAC address.

Switches provide significant scalability on a network. Switches are normally connected to each other by way of trunk links.

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What is Anycast and How it worksSubmitted by Sarath Pillai on Mon, 01/13/2014 - 15:55

If you try to access slashroot.in from US the request will be routed to the Linode London data center. If you try to access slashroot.in from Asia, again the request will be routed to the same Linode London Data Center. Take one more case, and try to access slashroot.in from Europe (Ireland) the request will be again routed to Linode London. 

The bottom line is, You will be routed to Linode London, no matter from where you access. 

There are two primary problems associated with this architecture. They are mentioned below. 

1. What if something happens to Linode London Data Center, and it goes down due to some problem (this wont happen, i love linode, and they are the best VPS solution providers out there, I will write a detailed post about my review regarding Linode. Just take this as an example.)

2. Second problem is if a user from Asia (say India for example), access my site, that user has to unnecessarily suffer a latency of few hundred milliseconds. The problem is with everyone. Say a person accessing my site from US, he will still suffer a little latency as his packets needs to travel all the way to London. 

 

This kind of an architecture where there is only one destination server for all sources (no matter from where the request comes from) is called as

unicasting. This is the highly used networking solution on the internet today. There is one destination server, with an ip address assigned to it, and it will answer all the requests. 

Traceroute is an awesome tool to check the path your packet is traveling. If you are new to traceroute, i will recommend reading the below post to understand how Traceroute works. 

 

 

This kind of an architecture works well for small to medium range of websites. But once your website becomes too large and starts getting heavy traffic, it will have a sever performance impact, and need to look for other optimum solutions. 

Imagine server's like the DNS root servers. There are 13 of them, which needs to be available all the time. Root servers are one of the most critical infrastructures on the internet. Due to this reason, anybody accessing it needs to get the result in the possible minimum latency. Hence DNS root servers uses Anycasting for this purpose. Apart from achieving a better latency, anycasting also provides redundancy. we will be discussing all of that in some time. 

Read: DNS Root Servers 

Here is where anycasting comes into the picture. Although in the beginning anycasting was only used for DNS. These days Anycasting is used for normal HTTP web sites. We will look into that part later. 

 

What is Anycast? 

You might have already heard the below terms in networking. These are very commonly used.

Unicast (one sender and one receiver. This is the most commonly used type. While you are reading this web page, you are using unicast type.)

Broadcast & Multicast (This includes one sender and multiple receivers. A good example of broadcast is the ARP request send by a computer on the network to all others. In Multicasting one or more senders can send data to multiple receivers. Multicasting in IPv4 is implemented by a special class of IP addresses reserved for this purpose. All those hosts that are part of that specific class of multicast address will receive the message send to that multicast address.) 

Anycasting is completely different from the above two types. A good definition of anycasting is given below. 

Anycasting is a method used to advertise one IP address from multiple points in the network topology, and with the help of dynamic routing method, the traffic is delivered to the nearest point. 

Although anycast works by having multiple receivers, only one receiver is selected from all the available ones. Hence in a way its a point to point communication with the nearest address. Also the sender does not care which receiver from the possible list is selected (as all of the receivers will be providing the same service and will be mirrors of each other.). 

A single anycast address is assigned to multiple hosts providing the service. And the routers in between does the job of selecting the best and nearest destination. A sender will send a request with the anycast address in it packet header and the routers then run the entire show of delivering it to the nearest location. 

But the main point to note here is the criteria used to select the receiver from the available list of multiple anycast destinations. There are different schemes/criteria that can be used for this selection. Before getting into that part, let's have a look at a diagram that represents the anycast basic network topology. 

 

 

In the above shown example topology diagram, two servers are shown. Both these servers are part of anycast group and are assigned with the same ip address of 10.1.1.10.

When client 1 needs to access the server its routed to the nearest server by Router 1. And whenclient 2 wants to access the server its routed to the nearest location (through router 3 and router 5). 

It is now clear from the above shown basic diagram, that there must be some criteria to select the destination server. There are different criteria/scheme that can be used in anycast for determining the best destination server. Let's see two main schemes that can be used in anycast. 

  IP Anycast or say Network Layer Anycast: If the destination server is

selected by the routing method, in other words users directed towards a destination server that needs few number or router hops in between, then it is called as network layer anycast.

Application Layer Anycast: If the destination server is selected by calculating the availability of the server, current number of connections, response times etc, then its called as application layer anycasting. But in this method, does not

depend on the network but depends on an external source which continuously monitor the statistics (like current number of connections, response time etc.) 

Network layer anycast is the highly used type of anycast in the internet. In the beginning anycasting was only used for DNS. Why only DNS ? The reason is described below. 

In the previously shown diagram, which describes the basic working of anycast, you can see that the same service is provided by multiple instances in different locations reachable by different paths. The idea behind anycasting is to reduce latency and increase redundancy. DNS works on UDP (which is a connection less protocol.)TCP is a connection oriented protocol, which means services using TCP requires a successful connection to be established first. Even protocols like HTTP works over TCP (yeah HTTP itself is not stateful, which means each request is independent of the other.). But a connection should be made to the destination server. In case of anycasting if something happens to one of the anycasted instance, the routers will stop sending traffic to them, and will select the next nearest anycast node. 

Read: How a TCP connection is established 

But in that case, if suppose a user was already browsing a web page (consider an HTTP anycast in this case), the already established TCP connection to the node will break (as that node is not available now), and routers will forward the traffic to the next nearest node (but as this is a different node, with the same ip address, the tcp connection needs to be established again.) 

Due to this problem, anycasting is mostly used for single request single response protocols. DNS is a single request response protocol. It does not matter which server replies you, because each request is independent, and no tcp connection is required. 

If you are new to DNS, please refer the below articles to understand some basics of DNS and its related topics. 

Read: How DNS worksRead: Iterative and recursive DNS queryRead: DNS zone file and its content 

An important thing to note, before going ahead.... 

Anycast was not designed for load balancing. The main purpose of anycast is to achieve reduced latency and redundancy. However depending upon on the way it is configured it gets a slight load balancing effect. 

There is no mechanism by which you can identify by looking at the ip address, whether its an anycast ip address or unicast. For example, 192.5.5.241 is an anycasted ip address and 212.71.233.103 is a unicast ip address. Both are ipV4 addresses. A special range of ip address is reserved for anycast in IPv6. But in IPv4 the normal unicast address space is used for anycast purpose. Hence by looking at the ip address you cannot identify whether its anycast or unicast. The only mechanism to identify it is to do traceroute from different locations. 

The ip address 192.5.5.241 is an anycasted IP address. How am i too sure about this?. Am sure about this because of two reasons.1. Its the IPv4 address of F DNS root server.2. Tracerouting from different locations around the world will make you reach the same IP in different locations. (mostly the nearest from the source.) Traceroute to DNS F root server from India is shown below.

 

My traceroute is going to Atlanta US (see the 17th and 18th lines above). Isn't that amazing?. The same ip at different locations on the internet. The F root servers are located at around 50 locations around the globe. You can find the entire list at the below link. 

F root server locations (You will find the Atlanta and HongKong locations in this list.)

 

To understand how routing on the internet works, we need to first understand a little about certain terms and protocols which makes internet work. Internet works on a trust relationship. My network will depend on an

another network (managed by somebody else)to reach some other network. To understand how routing in internet works we need to first understand two things. Domains and inter domain routing. Consider domains as a network under an independent administrative authority. Inter domain routing is described in terms of the number of domains it has to transit or (pass through) to reach a destination address of interest. This entire show of inter domain routing is handled by a protocol called as BGP (Border Gateway protocol). 

How packets travel inside a domain is up to the domain administration. In other words the domain authority can use any protocol to provide communication and proper delivery inside the domain. As things that happen inside the domain is internet, the protocols that will be used inside the domain is classified as Interior Gateway Protocol'sAs a domain is independent and is handled by an independent administrative authority, this domain is broadly called as Autonomous System's. You will rarely hear the term domain, because its broadly classified and generally referred to as Autonomous System's. Or AS 

Am quite sure that you have already heard about the below definition of the internet. 

Internet is a large network made by interconnecting small networks. Or network of networks. 

As we now know what an Autonomous System is, we can also say that internet is a large collection of interconnected Autonomous systems. But yeah there must be some mechanism by which you can uniquely identify the domains or say AS (autonomous systems). For that Autonomous system's are numbered. 

AS numbers are integers ranging from 0 to 4,294,967,295. IANA(Internet Assigned Numbers Authority ) maintains the entire list of AS number's. You can have a look at AS number's in the below link. 

AS numbers 

As we discussed earlier, BGP is the protocol which runs the entire show in inter domain routing. And BGP makes use of AS number's. Let's see how AS number's are used in BGP. 

 

 

In the above shown diagram ROUTER 1 receives two different paths to reach 172.16.200.0/24 network. ROUTER 1 can reach the server 172.16.200.200 through two different paths (please note that the servers are different.).  

If you see the routing table of ROUTER 1, you will see it has two routes for the subnet 172.16.200.0/24. The routes look something like the below. 

1. 172.16.200.0/24 AS path (2)2. 172.16.200.0/24 AS path (3,4)

 

The left most number in the AS path is the AS number from which the router got the route announcement information. So AS path (3,4) means the router received the address advertisement from AS 3(which is its neighbor), and the right most number indicates the AS from which the address advirtisement originated.  

Now the normal behavior of BGP(if it has multiple routes to reach the same address prefix) is to select the path that is the shortest to reach the destination.  Shortest in terms of AS's it has to go through... 

In anycast the same address prefix is announced from multiple locations. And most of the time a router has multiple paths to reach that address. The important point is that in anycasting most of these paths will lead to a different server with the same service. Hence if something happens to one of your anycasted server, you can withdraw the routes to that particular location, and the traffic will then start flowing to the next nearest location.  

Please note the fact that explaining BGP and AS path selection is beyond the scope of this article...The

things explained here will only be useful to get an idea about how anycasting works in the real world. 

 

What are the main advantages of using Anycast? 

One of the major advantage is to reduce latency in response. A user accessing the service from a particular location will be directed to the nearest end point providing the service.

Higher service uptime. An issue or technical glitch in one of the anycasted resource will not affect the other one in another locations, due to which users can be routed to that location. 

Better resistance against Distributed Denial Of Service Attacks.  

Large scale attacks which consume the server bandwidth and resources are generally executed from multiple locations around the world. The main motive of such attacks is to make a service or website unavailable to a legitimate client. 

 

If the attack originates from a single source address, it can be blocked to a certain extent. But what if the attack originates from 100 different geographical locations and all sending junk traffic to one particular service(for this purposes attackers normally use some thing called as botnet, which are computers infected by malicious programs, and are under control of the attacker.). A normal unicasted service will go unavailable in such conditions.

 

Attackers use botnet to send junk traffic, because they themselves does not require a large bandwidth to send it to the victim server. A botnet under control of an attacker can generate large amount of traffic (which is basically combined traffic from all infected hosts around the globe).  But if the target is using Anycast, such attacks can be mitigated to a larger extent. 

 

Because the attack volume gets distributed to all anycast nodes (As the infected hosts sending the traffic are also from different geographical locations, the traffic will be received by their respective nearest anycast address.)

 

Disadvantages of Anycast: 

Anycast is not suitable for Long Lived session protocols. For example, its not suitable for TCP and connection oriented stuff. Although if the routing is stable and no fluctuation occurs then it can also be used for TCP protocols like HTTP. I must say some major CDN (Content Delivery Networks) providers already use anycast as their primary mechanism for improving performance and reliability of HTTP.

A strategic distribution of nodes around the world must be made, with reliable upstream providers for a perfect anycaste architecture. Rate this article: 

5

So what’s the reason for having wires run ‘straight’ from one pin to the other?

The answer lies in the fact that networked devices send and receive signals on specific wiresof an Ethernet cable.

Computers Send and Receive On Specific Pins

Computers can send data across a network, if they have an Ethernet cable plugged into the jack of their network interface cards (NIC’s).

The data – in the form of bits – moves from the NIC and down to the eight pins of thenetwork port on the machine. From there, the bits move to the pins of the RJ45 connector of the Ethernet cable plugged into the network port. Finally the bits get sent along two of the wires to the destination device at the other end.

The question is; which pins – on the network port of a computer – are used to send data?

The NIC on a computer sends signals on pin 1 and pin 2.

The signal will be sent down whatever wires are connected to these two pins.

Send and receive pins on the network port of a computer

 

Turning our attention to the other end of the cable; what happens there – at the destination device?

Let’s assume the PC is connected to another networking device – a switch or router. So a cable runs from the RJ45 port on the computer to an RJ45 port on the switch/router. The RJ45 ports of a switch or router are set up by default to receive signals on pins 1 andpins 2.

See how things are matching up so far?

The computer sends on pin 1 and pin 2 and the switch/router is receiving or ‘listening’ on the same pins.

On the ports of a switch or router, data is received on pins 1 and 2, and sent on pins 3 and 6.

 

Now let’s address which pins are used when switches and routers transmit data back to the PC.

By default, a switch or router send their signals on pin 3 and pin 6 from their RJ45 ports.

So which pins does the NIC of the PC receive on?

You guessed it – the same pins 3 and 6.

When you plug a straight-through cable into the network jack of a computer; you are providing the correct paths for signals to be sent and received between a PC and aswitch/router.

A straight-through cable does this by:

connecting the sending pins 1 and 2 on a PC, with the receive pins

1 and 2 at the switch/router

connecting the sending pins 3 and 6 – at a switch or router – with

the receive pins 3 and 6 at the PC. 

Connecting PC’s to switches and routers, using a straight-through Ethernet cable, is your standard way to get network connectivity to the machine. The PC and switch (or PC/router) are considered to be ‘unlike’ devices – which is pretty self-explanatory, and in effect gives you a rule when to use straight-through cables:

 

Use straight-through cables to connect unlike devices on a network

 

When would you use a crossover cable?The term crossover simply refers to the crossing of wires at one end of an Ethernet cable. This is the difference between a cross over cable and a straight-through cable.

In the picture below, you can see that four wires are switched or crossed over to different pins at the other end of the cable. This time, the wires connected to pins 1 and 2 on one RJ45 connector, terminate at pins 3 and 6 on the other RJ45 connector.

But when would you use a cross-over cable and why?

 

If you want to connect two computers directly to each other, or connect a switch to another switch – you would have to use a cross-over cable.

 

Take a PC-to-PC connection as the first scenario.

The send pins on both machines are the same: pins 1 and 2. Likewise, the receive pins on both sides are 3 and 6.

So using a straight-through cable to connect two PC’s causes a problem because you’d be connecting ‘transmit to transmit’ pins, and ‘receive to receive’ pins, and nothing would get through.

Performing a ‘crossover’ by wiring the send pins 1 and 2 to the receive pins 3 and 6, solves the problem and allows correct communication between the devices. For a quick way to network two PC’s – crossover cables are a great solution.

What about a switch-to-switch connection?

Same again, use a cross-over cable.

Remember that on a switch, pins 1 and 2 are the receive pins, while pins 3 and 6 are used to send. The cross-over cable still does its job by connecting the send and receive pins on both sides of a switch-to-switch connection. The direction in which the signals are sent along the wires may be flipped around, but the two switches will communicate correctly.

The rule is:

Use cross-over cables to connect like devices on a network

 

Knowing the difference between a straight-through cable and crossover cable, is a basic requirement for PC and network technicians. That’s why you’ll see the topic covered in theCompTIA Network+ and Cisco CCENT certifications especially.

You now understand how the wires – within straight-through and crossover cables – connect to the pins of their connectors, and why they do so.