How to start, close, and set up an Ubuntu firewall

Http://blog.sina.com.cn/s/blog_866c5a5d0101ihxv.html

That's all you have to say.

sudo ufw enable|disable

Because the Linux original firewall tool iptables too cumbersome, Ubuntu defaults to provide a firewall tool based on iptable UFW.

Ubuntu 9.10 Default is the UFW firewall, it has supported the interface operation. Run the UFW command at the command line to see a list of possible actions for the prompt.

One of the simplest operations: sudo UFW status checks the state of the firewall, and my return is: Inactive

sudo UFW version firewall versions:
UFW 0.29-4UBUNTU1
Copyright 2008-2009 Canonical Ltd.

Ubuntu system has UFW installed by default.

1. Installation

sudo apt-get install UFW

2. Enable

sudo UFW enable

sudo ufw default deny

After running the above two commands, the firewall is turned on and turned on automatically when the system starts. All external access to the native is turned off, but the native access is normal externally.

3. Turn ON/off

sudo ufw allow|deny [service]

Open or close a port, for example:

sudo UFW allow SMTP allows all external IPs to access native 25/TCP (SMTP) ports

sudo ufw allow 22/tcp allows all external IP access to the native 22/tcp (SSH) port

sudo UFW allow 53 allows external access to 53 ports (TCP/UDP)

sudo ufw allow from 192.168.1.100 allows this IP access to all native ports

sudo ufw allow proto UDP 192.168.0.1 port 192.168.0.2 port 53

sudo UFW deny SMTP prevents external access to the SMTP service

sudo ufw delete allow SMTP to delete a rule established above

4. View firewall status

sudo UFW status

For general users, only the following settings are required:

sudo apt-get install UFW

sudo UFW enable

sudo ufw default deny

The above three commands are safe enough, if you need to open some services, then use sudo ufw allow to open.

Turn firewall on/off (the default setting is ' Disable ')

sudo ufw enable|disable

Convert log status

sudo ufw logging On|off

Set default policy (e.g. "mostly open" vs "mostly closed")

sudo ufw default Allow|deny

Licensed or shielded port (you can view the list of services in "status"). You can specify a service name that exists in/etc/services in the "Protocol: port" mode, or through the meta-data of the package. The ' Allow ' parameter will add the entry to/etc/ufw/maps, while ' deny ' is the opposite. The basic syntax is as follows:

sudo ufw allow|deny [service]

Displays the listening state of the firewall and port, see/var/lib/ufw/maps. The numbers in parentheses will not be displayed.

sudo UFW status

UFW Use Example:

Allow Port 53

$ sudo ufw allow 53

Disable Port 53

$ sudo ufw delete Allow 53

Allow Port 80

$ sudo ufw allow 80/tcp

Disable Port 80

$ sudo ufw delete Allow 80/tcp

Allow SMTP ports

$ sudo ufw allow SMTP

Remove licensing for SMTP ports

$ sudo ufw delete allow SMTP

Allow a specific IP

$ sudo ufw allow from 192.168.254.254

Delete the above rule

$ sudo ufw delete allow from 192.168.254.254

The Linux 2.4 Kernel later provides a very good firewall tool: Netfilter/iptables, he is free and powerful, can control the incoming and outgoing information, it can achieve firewall, NAT (network address translation) and data packet segmentation and other functions. NetFilter work inside the kernel, while iptables is the table structure that lets the user define the rule set.

But Iptables's rules are slightly "complex", so Ubuntu provides UFW as a setting tool to simplify some of Iptables's settings, with the background still iptables. UFW is the abbreviation of uncomplicated firewall, some complex settings or to go to iptables.

UFW related files and folders are:

/etc/ufw/: There are some UFW environment settings files, such as Before.rules, After.rules, sysctl.conf, ufw.conf, and IP6 and Before6.rule for After6.rules. These files generally follow the default settings for OK.

If the UFW is turned on,/etc/ufw/sysctl.conf will overwrite the default/etc/sysctl.conf file, if your original/etc/sysctl.conf has been modified, if you start UFW,/etc/ufw/ Sysctl.conf in the new assignment, it will overwrite/etc/sysctl.conf, otherwise the/etc/sysctl.conf shall prevail. Of course you can set which sysctrl.conf to use by modifying the "ipt_sysctl=" entry in/ETC/DEFAULT/UFW.

/var/lib/ufw/user.rules This file is a set of some of our firewall rules, open probably can see, sometimes we can directly modify the file, do not use the command to set. After the change, remember UFW reload restart UFW make the new rule take effect.

Here are some examples of the UFW command line:

UFW enable/disable: Open/Close UFW

UFW Status: View the UFW rules that have been defined

UFW default Allow/deny: Inbound access defaults to allow/deny

UFW allow/deny 20: Allow/deny access to 20 ports, 20 can be followed by/tcp or/UDP, indicating TCP or UDP packets.

UFW allow/deny SERVICENAME:UFW Find the corresponding service port from the/etc/services and filter it.

UFW enable proto TCP from 10.0.1.0/10 to native IP port 25: Allow self-10.0.1.0/10 TCP packets to access 25 ports on this machine.

UFW Delete Allow/deny 20: Delete the previously defined rules for allow/deny access to 20 ports

How to start, close, and set up an Ubuntu firewall