Check Open Ports from inside and outside the network.

Hi today i will discuss about how we can check for Open ports for a device. However there are many tools available on net to check open ports. My favorite is Look@Lan. But we should must know how to check for open ports manually.

For this we have inbuilt functionality in our systems also – telnet. In Windows 7, you have to enable it. You have to follow these below steps to enable telnet ...

1. Go to Control Panel --> Program and Features

2. Click on “Turn Windows Features On or off”

3. A Pop Up window will appear.

4. Click on Telnet Client and Click Ok

This will install Telnet Client on your system.

If you are using Linux system, it must be preinstalled or you can install it according to Linux Flavor.

Suppose you are opening a port over firewall and you want to check whether it is working properly from outside to internal network or from Inside network to outer world.

Like i will check Port 443 is opened for Google or not ...

You will find the message “Escape character is '^]'.” , blank screen or message according to the Port serviced. For example if I am checking the SMTP Port you will find the Screen looks like.

So message may be vary from port to port. If the Port you are checking is blocked or disabled you will find the message like ...

Using the same procedure you can check incoming connection also to your firewall, using NATING and PATING.

I hope, this post will be helpful for you to manage your firewalls and Networks.

NATING and PATING

NAT stands for Network Address Translation  and PAT stands for Port Address Translation. For the understanding NAT you should understand how it works. For example if you are opening a web site in your office or in a cafe. There are hundred of computers sharing a common IP. Have you ever experienced that you requested abc.com and your friend requested for xyz.com at the same time but your computer opened xyz.com and your friend's computer opened abc.com ?? Answer is No. While opening a web site your computer send the request packet contains you public IP. After receiving the request from your computer Web site's Server send the requested page to your public IP. Now suppose you are opening XYZ.com from IP 192.168.1.1 and at the same time your colleague is opening ABC.com from 192.168.1.2. Both of the computers are sharing the same public IP e.g x.x.x.x
Both Web site's Server i.e. ABC.com and XYZ.com will serve the request to IP x.x.x.x. After reaching the request to your router or firewall, this request redirects to concerned local IP.

Similarly PATING works, using NATING and PATING you can use single WAN IP to serve multiple Servers in your network for the requests coming from global network.

For example you are running 2 Web servers, both are running on port 80 and you have only one WAN IP x.x.x.x. In this scenario you can use x.x.x.x to sever both the servers using PATTING. For the outer network you have to use different ports but after PATING it will redirect for different servers. e.g. http://x.x.x.x:80 and http://x.x.x.x:8080

NATING and PATING takes place on firewall level. Using the same you can use single WAN IP to serve multiple servers using common port.

Network Security

In the age of global networking, securing your network is very much essential. When you are connected to internet, you become a part of that global network. While accessing any website or checking your mails, you re accessing resources of that server. similarly when you are accessing resources of another system on internet, other systems can access your resources.

Accessing Internet or being part of this global network is very risky today in corporate environment. According to my experience 99% of employees even don't know that they are under threat. Lots of data is going outside the corporate network without the knowledge of users and administrators.

Reality is more worst for home users. Most of the users are not concerned about the security for their system or network. They have no idea what comes in or goes out. Their only aim is to access the website or check their mails. Most of the users are using wifi routers. They have no idea what is the security of their wifi. If you go to a residential building or any residential area, their is a great possibility that you will find an open wifi to access. On the other hand lots of users are using WPA1 still and it is very easy to crack, sometimes seconds to crack. Normally users don't change the default passwords. While using wifi routers users should change the Default admin password. As well as i will advise every body to disable dhcp and change the ip series. so that if unfortunately some one cracks your wifi, cant access your network.

Exploiting is very common now a days. Sometimes it is difficult for the firewall to recognize malicious traffic to block, as most of the time malicious traffic also travels through common ports i.e. 80, 443, 25 etc. We can't block these common ports on firewalls. Even maually finding such traffic require a lot of training and experience.

While Securing any network you should keep 3 things in mind -

1. A Secure Network suppose that host is hostile.

2. A Secure Host suppose that Network is hostile.

3. A secure Application suppose that User is hostile.

If you are designing or configuring network with you should follow these concepts. Firewall hardening is important as logs are not always useful because most of the time its only postmortem activity. Its is always beneficial to become proactive. You should configure in such a way that outer traffic should not hit your servers directly. Proxies are the best for this purpose.

In the end i would like to say that hardening of your network is very much important but training and educating the end users are the same important aspect of this process. very few companies are going with these aspects. Most of the companies even don't know that they are under threat and what data is going outside their network.

Hi All !!!

This is Sumit Shrivastava, Working as an IT Manager in LT Foods. Maintaining Windows, Linux and AIX Servers, Firewalls, Routers and Network Security

I am starting my blog for networking personals. It would be also helpful for non networking personals also.

I got idea to start my blog for helping for the guys who are entering this field and have don't have such experience regarding it.