Ethernet Hub - Physical Layer Device

Hub is a network device connects multiple devices and makes single network segment. Hub works in Physical layer of OSI Reference Model. Since it is a layer one device, it does not have the feature to read the signals it transmit. All the devices connected to the hub feel they are connected to the same physical wire. So we can say hub has single collision domain. In other words a hub simply repeat the signal it receives. Let us check the working of hubs.


How Hubs work

When a computer connected to a hub sends packets, hub broadcast the packets to all the ports except the one it came from. Here we can see the difference between Switch and hub. Hub does not read the packets and it broadcast to all ports but Switch is intelligent device and read the packet and just unicast it. So Switch is more efficient compared to hub. Another problem with hub is the higher chances of packet collisions. We know hub has single collision domain and the chances of collision is very high.


Now a days very rarely we use hubs to connect network devices. Most networks use Switches to connect multiple network devices in a single network.

Other Tutorials

  1. Router Cascading Guide

  2. Router and Major Routing Protocols

  3. How to Power Cycle a Router

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Internet Control Message Protocol (ICMP)

One of the important part we need to do while troubleshooting a network is to check the connectivity of two devices. We have many utilities to check the connectivity and availability of destination device. All these utilities are based on ICMP, defined in RFC 792. Internet Control Message Protocol (ICMP) is used to send error and control information between devices which support TCP/IP. Utilities like ping, tracert, pathping etc works using ICMP. This tutorial explains the functions of Internet Control Message Protocol and the list of error messages generated by ICMP.

Important Functions of ICMP
  1. Send echo requests from a TCP/IP device to another

  2. Responds to Echo request

  3. Helps to find routing path issues

  4. ICMP echo message verify the availability of destination

List of Messages Generated by ICMP
  1. Address Request

  2. Address reply

  3. Destination unreachable

    To learn more about the Destination unreachable message generated by Internet Control Message Protocol, visit the links below.


  4. Subnet Mask Request

  5. Time Exceeded

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DMZ In Network Security (Demilitarized Zone)

Now most of the modern Small Office Home Office routers offer DMZ host feature. For those who don't know about the use of DMZ, this tutorial may give an overall idea about it. If you place a device in your network in DMZ, that device won't have much access to other devices connected to the network. Device placed in DMZ is more exposed to external threats as it is logically placed outside the network with limited security. Also all ports of DMZ host are open and exposed to external network. DMZ host has its on merits and demerits.


What is The Use of DMZ in a Network

If you are a hardcore online gamer, you know the hurdles created by the router firewall and NAT. In most cases simple port forwarding allows you to continue online gaming but rarely some users face issues. Ultimate solution for the firewall issues in online gaming is to place your gaming computer in DMZ. However, after this step, your gaming computer is no longer protected by router firewall. Also your computer face limited connection to other computers in your home network.

Technically DMZ host is outside the network. So other hosts in your network is safe even if DMZ host is compromised. Though DMZ computer is compromised by a hacker, attacker will not get access to other devices in the network. So you can run a web service on your computer which can be placed in DMZ without risking the security of other devices in your network.

Further Readings
  1. Denial of Service (DOS) attacks Tutorial

  2. How to Improve The Speed Of Your Internet Connection

  3. Port Forwarding On Belkin Wireless Router

  4. Port Forwarding On Linksys Wireless Router

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