There are times when you might need to filter the traffic on your firewall using MAC addresses instead of IP addresses,
iptables has the option to do it.
From the man page of iptables:
Note that this only makes sense for packets coming from an Ethernet device and entering the PREROUTING, FORWARD or INPUT chains.
You may want to insert this line in you firewall script.
iptables -A INPUT -m mac --mac-source 00:11:2f:8f:f8:f8 -j DROP
This way the packets comming from the network element with the MAC address 00:11:2f:8f:f8:f8 will be denied.
That is if you want to block the incoming packets to the firewall, but the blocked machine may still be able to send packets across the firewall, so to block those packets, you may want to add also this line.
iptables -A FORWARD -m mac --mac-source 00:11:2f:8f:f8:f8 -j DROP
Nmap is a wonderful tool specially for debugging, there are lots of times when you need to know if a port is open in a server, or maybe blocked by a firewall, or just to test your iptables rules.
Here we will learn how to use it at the command line, and using its GUI front end, nmapFE and Knmap.
Well, so what does nmap does?
From the man page:
Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks, although it works fine against single hosts. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. While Nmap is commonly used for security audits, many systems and network administrators find it useful for routine tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime.
As you can see it is a really useful Linux tool.
How to use it
Nmap has lots of options, so we are going to focus on only some of them.
sudo nmap -sS -O 127.0.0.1
sudo nmap -sU 127.0.0.1
sudo nmap -sS -O -p 20-25 127.0.0.1
sudo nmap -sS -F 127.0.0.1
you can check the long nmap man page
nmap Front End (nmapFE)
This is one of its front ends to install it run:
For Fedora / Centos
sudo yum install nmap nmap-frontend
For Debian / Ubuntu
sudo aptitude install nmapfe
On target you put the IP or IPs you want to scan, select the scan type, if you want TCP SYN, UDP, Connect scan, or other, the most used are SYN and UDP if you want to scan for UDP ports. Also select the scanned ports, you can scan the default ones, All, fast (only the ports in nmap-services file).
Select if you want to use the discovery option, if you want to ping and which type of ping you want to use to discover network nodes if you have specified an IP range to scan.
Useful if you want to send the output to a file.
Lots of other tools, if you want you can enable verbosity of debugging, and if you want IPv6 support.
KDE Nmap (knmap)
To install it
For Fedora download the rpm here
sudo rpm -ivh [downloaded package]
For Debian / Ubuntu
sudo aptitude install knmap
Its interface has divided the options in a very convenient way, in the common options you will see the target IPs, the port range and if you want it to resolve names.
Here you select if you want to scan all ports, perform a fast scan, IPv6 support, Operating System detection, verbose, and other options.
In compound options, you will find a lot more options to play with, you can select which interface to use, which IP, and even if you want to spoof your Mac address!
Ping and scan options is like the discover and the scan tabs of nmapFE together.
Nmap is a must have tool for network and security administrators, also the GUI front ends are good and easy ways to use them, and also to learn how to use them, because you can discover new applications, and with nmapFE you can see the command that is going to be executed, another good point for knmap is that it has the possibility to save profiles, with all the options you have enabled, so your next scan is easier.
AMaVis : (e-mail Virus Scanner) It scans e-mail attachments for viruses using third-party virus scanners available for Linux. It Supports courier, exim, qmail, postfix, and sendmail. Built-in defense against Denial of Service (DoS) attacks
sudo apt-get install amavis-stats
Avast! : It is an anti-virus program from ALWIL Software based in Prague. This is a freeware for home users and non-commercial use only. It is a good software for virus protection, with built-in anti-spyware and anti-rootkit security. Work on all modern linux distributions. It scans archives like rar, tgz, zip, gzip, tar, iso, rpm etc.
AVG Free : AVG Free for Linux is a commercial-grade antivirus software. It can be used on a single computer and is used for private, non-commercial use only. AVG Free has both command line and a graphical front end are available. It provides frequent updation and total professional security.
ClamAV : Clam AntiVirus designed especially for e-mail scanning on mail gateways.It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. The core of the package is an anti-virus engine available in a form of shared library.Built-in support for document formats including MS Office and MacOffice files, PDF, HTML and RTF. It supports archives like rar, tgz, zip, gzip, tar, iso, rpm etc
sudo apt-get install clamav
$ sudo apt-get install gshutdown
( or use synaptic package manager)
Some recent posts showing that your linux box is not secure unless you installed a grub Password.
If you are an administrator of a highly sensitive server, you must do it.
To add a password for grub, first you must generate an md5 password hash using the grub-md5-crypt utility: grub-md5-crypt
The command will ask you to enter a password and offer a resulting hash value as shown below:
Password: (enter new password)
Retype password: (repeat password)
Add the resulting hash value to the file /boot/grub/menu.lst in the following format:
password –md5 $1$s3YiK$M3lxAbqA6JLm2FbDWnClQ0
To require use of the password for entering single user mode, change the value of the lockalternative variable in the file /boot/grub/menu.lst to true, as shown in the following example.