1. RouterOS by Example. Understanding MikroTik RouterOS Through. Real Life Applications. 2nd Edition. Stephen R.W. Discher. RouterOS by Example - Stefsdphen paimarlangkefgeekb.ml - Ebook download as PDF File .pdf), Text File .txt) or read book online. this book is great for router OS. Example – Setting the System Clock Manually and Setting the Time Zone . is a growing company with a full-featured router operating system, RouterOS.
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MikroTik RouterOS™ v Reference Manual .. Application Examples. .. PPP Application Example. RouterOS by Example - Stefsdphen paimarlangkefgeekb.ml Click the start the download. DOWNLOAD PDF. Report this file. Description. this book is great for router OS. RouterOS, and have working examples that you can emulate and change to .. example of this may be that you have a hotspot that needs more than
Start your favorite serial terminal program Hyperterm or Putty work fine. Putty will be used for purposes of this example. Start NetInstall on the PC. You should see a window like this: Click the Net Booting button and configure an IP address to give the board to be flashed on the same subnet as your PC. In this example, use Next, power up the board and watch the terminal on Putty. When the screen says Press any key within 2 seconds to enter setup.
Next type the letter o then 1 and then x. Case of the commands is important. The board should then boot from the NetInstall instance using the bootp protocol. If you do not see a version there, try browsing to the. Note : The download page on www. It also allows you to download the Combined package or All packages.
Typically you will want the Combined package as it contains the most common packages in a single file. If you need any optional packages, then the All packages zip file is your answer. Click the Install button to install that version. Note: If you are attempting to recover a board for which you do not have the password, do not click the option keep old configuration as it will also keep the password, thereby still rendering the board inaccessible.
Note: Netinstall can be used in the manner described above for recovering a board for which the password has been lost or for an initial install on a PXE bootable device, compact flash drive, hard drive, etc. Creating the Basic Configuration Due to the power of this device, even a basic configuration can be daunting.
I will walk you through the creation of a basic configuration that will allow you to access this device easily until you are more experienced at configuring it. I will not explain the steps here, and instead will explain them in depth later in the book. When you first power up the device and connect to it using WinBox as described on page 27, provided the device has not been configured, you will see a window like this: I recommend you remove the default configuration, and this will allow you to create your own without anything cluttering things up.
Note that you should be accessing the router via the MAC address as previously explained with WinBox. If you are in through the default IP address of To assist you, I have developed a script you can simply paste into the router and it will configure everything for you and get you started on the right track.
The script is a text file so copy it to your clipboard and then in WinBox, click the New Terminal button and inside the terminal window right click with your mouse and select paste and watch the script configure the necessities.
At this point you should have a router with ether1 ready to connect to the Internet provider with the following assumptions: Ether1 is the WAN port; it will expect DHCP from the provider. If you have a wireless card, it will broadcast 2. It will also pass out DHCP addresses. You can connect with a cable to ether2 or wirelessly. The router will provide basic Internet access, has no admin password, no encryption and no firewall so please understand there is no security provided!
If you do not have Internet access and enjoy typing, you can type the commands on the following page into a terminal window instead of pasting.
Interfaces Interfaces are the physical ports that allow input and output connections to the router. Interfaces are accessed from the Interfaces button. Interfaces can be renamed by double clicking on the interface name in the Interfaces list window and then setting their Name on the General tab.
This will help you identify them physically or logically or assist you with troubleshooting. I suggest using comments on interfaces rather than renaming them. My reason is that most enclosures are labeled with the same interface name as it appears in RouterOS and keeping them the same makes things simpler.
The assumption is made that you understand basic networking and subnetting and accept the fact that for two hosts to communicate on the same local area network or LAN, they must be on the same subnet or they will require the help of a router that has addresses on both subnets.
That being said, to add an IP address to a RouterOS device, it is first necessary to gain access through one of the methods previous described including WinBox through the MAC address, or through the serial terminal as outlined beginning on page If WinBox does not see your router, try a different interface or use the serial terminal method.
Begin by clicking the IP button and then Addresses. Click the plus sign to add a new IP address to the desired interface. The format for CIDR notation is Click ok to save the address.
UserManager is a totally separate package distributed by MikroTik and is basically their implementation of Radius server. User Management is a function within RouterOS and should therefore not be confused with the UserManager optional package.
Users can be created with three different permission levels. By default, there exists a user named admin with permissions of full. By default the admin password is blank. Obviously for security purposes, changing the admin password to something a bit harder to guess than a blank password is prudent, however, you may wish to create several users with various levels of access.
Note: This task can be centralized and the administrative effort of controlling user access can be simplified by using a central authentication mechanism such as Radius or MikroTiks UserManager. More on that on page In WinBox, users are created by clicking the System button and then the Users menu item.
The plus sign will add a user and allow you to set the password. Also selectable is the group and there are three by default. The group full has full read and write access to the router while read can only view the configuration and write can read and write the configuration.
These three default example groups provide some demonstration of the granularity with the rights you can give each of them. Dont be confused by the group named write.
The write group isnt substantially different by design, it just has a different set of permissions as created by default.
Typically, I recommend you create users with read access for anyone that doesnt need to change the configuration and full access for your trusted admins. Any deviation on this policy should be made on a case-by-case basis. From the System Button, select Users. From the Groups tab, you can double click a group to see their details.
As you can see, there are a lot of possible combinations of group permissions available: Your selections are dependent upon your individual circumstances. Example - User and Group Assignments and Policy User creation and group assignment is really simple and self-explanatory so instead of an example, a best practice might be more meaningful and useful. Here is an example of groups and access rights.
You are considering using a consultant to provide network evaluation and possible configuration but dont want him or her to accidently cause an outage in your production network. Before giving anyone the keys to the kingdom I recommend creating for him or her a user with read access. This way, they are able to view your entire configuration without actually being able to make changes. Once you are comfortable with their abilities, then you can change their group to full.
For Further Study UserManager If you arent ready to explore an advanced topic, you may skip this section and return to it later. Imagine you are a network administrator with various levels of technicians and admins. You want a centralized approach to user management and various levels of access to ensure your ability to terminate network access for an employee quickly.
The best and most scalable solution to this situation is MikroTiks UserManager. The installation of UserManager goes beyond the scope of this book and the MTCNA certification but a few instructions here can help steer you in the right direction. First, UserManager should be installed on a machine that is in a very stable part of your network with reliable power and connectivity so I suggest your NOC or data center as the ideal location. Since it is available as a package for RouterOS, it can be installed on a physical router or a virtual machine running the X86 version of RouterOS, the latter being my first choice.
The Dude is MikroTiks network monitoring program and is available for download at no charge on MikroTiks web site. UserManager creates a large quantity of log files and the availability of the extra disk space a virtual machine can provide is helpful. Once UserManager is installed and working, you will install a radius client on each router to authenticate from UserManager. I recommend setting the local admin password on the router to something difficult to guess and only known to you or a trusted employee.
This local user is always available to log into the device even if the UserManager server is unavailable. Then create users within UserManager for each of your technicians with the appropriate User Group. If a technician is terminated, you simply remove their account in UserManager to disable their access to the entire network. Obviously there are many steps in-between the portions I have described and the MikroTik Wiki is a great place to go for a step-by-step process to deploy UserManager.
Hopefully the pieces I have added here will fill in the remainder of the blanks and ensure a successful solution for centralized user management. MikroTik recommends that you upgrade your board to the latest version of RouterOS before beginning any configuration.
The operating system is in constant development and new features or bug fixes are frequently available, sometimes even monthly. The decision to do an upgrade on a production system on the other hand should be based on some basic logical reasoning such as: 1.
Is there a feature I want to add to my device that the new OS will provide? Is there a security vulnerability this version solves? Is there a bug fix this version provides? Do I need to upgrade to provide support for some new hardware? All of these are valid reasons to upgrade your device. As a friend of mine says, Every problem is the result of a previous solution.
Another one I am sure you have heard is if it isn't broken dont fix it. I think you get the point here, if the criteria expressed above doesnt apply, leave your router alone. It is doing its job and doesnt need your help, however, if you need to do an upgrade, read on.
Example Upgrading the Operating System 1. First, you must download the upgrade package from MikroTik. After web browsing to the MikroTik site, locate the download section and select the platform you want to upgrade. See page 36 if you have any questions about which file to download. Download the.
Typically the package you want is the stable version, combined package. This single file contains the same features that are installed by default on the device. Once the package is downloaded typically around 12 megs , launch WinBox and access through the devices IP address, not through the MAC address. As stated before, the Layer 3 method is the best for all normal router management.
Inside WinBox, click the Files button. This will open the Files List showing all the visible files stored on the router. Next, drag the package from your desktop to the files window. This can be a bit tedious, depending on how the files are sorted in the files window.
Dropping the file inside a folder will prevent the upgrade from taking place so use care to get it at the top of the list. One trick here is to click the Backup button in the Files List. This will produce and save a backup file, which sorts to the top of the list and allows you a little space in which to drop the upgrade package. The npk file doesnt have to be the top file in the list, but make sure it isnt in a folder.
Dropping the file in the area identified by the red arrow will produce the desired result: 7. Once the file has completely uploaded, issue a reboot command by clicking System and Reboot. Note: Pulling the power at this point will not upgrade the router; you must enter a graceful reboot using the reboot command due to the process RouterOS uses to update the device. After a few minutes, your router will return to operation with the new version installed. Confirm in WinBox: And in the Package List: Once the operating system has been upgraded, it is advisable to update the boot loader.
This is done from the command line by clicking the New Terminal button. At the command line type: The system will ask for confirmation so answer y. Then, reboot the system to upgrade the boot loader. This two-step process will ensure that both the operating system and the boot loader are compatible versions. Upgrading the boot loader ensures the hardware is best able to communicate with the software and although not required, is recommended.
Upgrading the boot loader with an x86 based system is not possible or required. Example Downgrading the Operating System Sometimes it is desired or necessary to downgrade the operating system. This is performed in the same manner as upgrading, however once the older package has been copied into the Files List, click the System button and select the Packages menu item.
In the Packages List, select all of the packages and click the Downgrade button. Reboot the router and the operating system will be downgraded. Note: I do not recommend running different versions of packages unless you know what you are doing.
To do so may be possible but can produce unwanted results. Example Upgrading using FTP If WinBox and the simple drag and drop method is not possible, you can use an FTP client to transfer the package to the router and then issue a reboot command.
Example Adding a Package Sometimes you find it necessary to add a package not already installed on the router. This may be true for adding a feature like UserManager or if you accidently uninstalled a package that you now need. Packages not included in the combined package may be downloaded as a zip file from the same page on the MikroTik site where you downloaded the upgrade package.
To install a single package: 1. Download the all packages and unzip on your desktop. Drag the package to your Files List as you did previously for the system upgrade. Reboot the router and the new package will be installed. Example Best Practice for Package Management I recommend uninstalling any packages you do not need or anticipate you will not need in the future. I also recommend disabling any packages you might need in the future but dont need today.
This will help secure your system, simplify the configuration and reduce system resources. I recommend the following packages be the minimum installed and enabled. By default, the identity is MikroTik, which is obviously not very useful in your network so it is a good idea to make setting the router identity part of your standard configuration routine.
The convention you choose is entirely up to you, but I have found that using the physical address of the client is often helpful to help troubleshoot at a later time. For example, setting the Router Identity to Smith Street is a good practice.
The router identity is found in several places. I suggest us. This manual introduces you with commands which are used Mikrotik And Ansible manual. Do the configuration of how many links you want and the way you want. Mikrotik Bangla Tutorial with Free Bangla e-book. Telnet Server. Cara Reset Mikrotik 3. Mikrotik RouterOS has lots of parameters and complexities which involves a steep learning curve and take longer time. It goes through the Winbox configuratoin utility and some of the basic setup procedures to turn your MikroTik device into a home or office wireless and wired router.
Step 6. Step 4. Mikrotik routerboard rbuas 2hnd in manual, not specified, mb. Overview, 2 Diagram. I then set an IP via command line so I can use winbox to finish my configurations.
Unix Shell Scripting 1. Please ensure that your hotspot is currently running as described before proceeding with this tutorial. Now I have them on site with a new controller setup and they cannot be discovered by the controller, I am assuming because they have been set up on a different controller. Straddle a tutorial vpn mikrotik pdf donkey, and ride along and take that big mouth trailer park hoochie with you!
The installation process should take about an hour, or longer. Switch config host Switch Once router Download of Mikrotik Most Wanted. Watermark theme. I will prepare a tutorial per week, and more if you have interested. Be careful and read step-by-step instructions before you proceed to setting it up.
In this tutorial we will go through a step by step guide to make it as simple as possible to learn and implement these setting s on your own routers. It can also be installed on a PC and will turn it into a router with all the necessary features - routing, firewall, bandwidth, management, wireless access point, backhaul link, hotspot, gateway, VPN server and more.
MikroTik Wiki. NAT 6. Look at this PDF file for full specs. MikroTik graphical user interface GUI will appear now. The console is used for accessing the MikroTik Router's configuration and management features using text terminals, either remotely using serial port, telnet, SSH or console screen within Winbox, or directly using monitor and keyboard. Leave a Reply, views, 5 so far. Download with Google Download with Facebook or download with email.
Mikrotik Router Configuration By. Submitted by admin, on June 14th, Here are the steps to help secure your Mikrotik RouterOS router via the command Mikrotik Router.
In summary. I could not have said it better myself. Each has its own unique value and by producing both you have more flexibility when disaster strikes or if you simply need to upgrade a device. A binary backup is not editable. I mean that every interface will be configured exactly the same as before thereby producing a clone of the original device configuration.
By accuracy. Chapter 6 — Backups I once saw a sign that read. A text-based backup on the other hand is editable and can be restored to different hardware platforms by doing some simple editing with your favorite text editor such as Windows Notepad.
In the Files window click the Backup button. Example — Creating a Binary Backup 1. In WinBox click on the Files button. It is also helpful to rename the file to something meaningful to you. Click to highlight it and then click the Restore button. Once the backup file is created it will appear in the Files List.
Once rebooted. The router will confirm the reboot. Drag the file from the list to your local drive or desktop for safekeeping. When a backup is restored. If the file to be restored is on your local drive. If the file is already in the Files List from a previous backup. It is also a good idea to include the date in all backup file names.
Example — Restoring a Binary Backup 1. Click on the Files button. Depending on the number and names of the files in your File List. A gold standard is a configuration that is used on all of your devices with general configuration options such as NTP client.
By configuring a single device with all of the standard options you normally want. Simply removing those configuration variables causes the file to load properly and typically without error. From there you can drag and drop it to your desktop for renaming and further editing. In particular. I recommend removing all of those configuration segments. At the root prompt. Open a terminal window by clicking the New Terminal button.
It is not necessary to specify the file extension.
Once you have all of your configuration sections. Example — Creating a Text Export text backup The text export is created from the command line only. A good way to fix this is to create another backup using the process above which will put the fresh backup at the top of your files list and thereby create some space above any folders.
Of course. A shortcut here is to type the command less the file name and then hit the tab key to display all importable files. Typing a portion of the file name and hitting the tab key again.
One way is to copy the text to your clipboard and then right click inside a New Terminal window and select paste. Drag the file to be imported into the File List root directory. Also note that the export is produced relative to the portion of the command tree you are in. Example — Importing a Text Backup There are several methods of using the text backup you have created and edited.
From there you can copy and paste parts of the file for use elsewhere. Another method is to import the file from the command line. By typing IP Address and enter. MikroTik delivers all of the features in all license levels and simply restricts the number of instances. Licenses are included with RouterBOARDs and licensing is typically not an area where you will need to spend much time for basic setups. The following chart displays the various license levels and their associated features: While many manufacturers require additional fees to add even standard base features.
Chapter 7 — Licensing One of the attributes of RouterOS that delivers the most value is the base feature set. On the other hand. Some additional things to know about licenses are that they never expire, level 4 and higher licenses include email support for up to 15 days after download, can support an unlimited number of interfaces, and they can only be used for one installation.
For example, if the board is intended to be a CPE customer premise equipment device, it comes with a level 3 license. Access point or AP boards come with at least a level 4 license and so on. Licenses cannot be upgraded but they can be downloadd and replaced.
For example, if you own a device with a level 3 license, you can download a level 4 license and install it on the device thereby turning it into an access point. Changing license levels is considered the equivalent of installing a new license, not an upgrade, so you will have to pay the full cost of the level 4 license and not just an upgrade charge. Licenses can be bought by creating an account at mikrotik. Example — Determining Your License Level To determine the level of license installed on your device, click on the System button and then.
Example — Install a License 1. To obtain a license key, repeat the procedure in the previous example and copy the Software ID to your clipboard. Create an account and log in at Mikrotik. download a new key using the Software ID and obtain the new key.
The key will look like this:. You can copy the key to your clipboard for installation. To paste the key into the router, select System License and click the Paste Key button. An alternate method is to use the. Click the Import Key button and browse to the. The Update License Key button is used to update the key to the new format as presented when upgrading from version 3 to version 4 and requires the laptop to have Internet access in order to complete.
There is no charge for this update. Chapter 8 — Firewalls Where there are options there is power. Where there is power there also can be complexity and therefore creating firewalls with RouterOS is often seen as an area of complexity where users fear to tread. As a result, many either make the decision to forego the firewall and hope for the best or copy firewalls others have created online and thereby never realize the power that a properly created firewall can have and the protection it can offer their network or their network connected devices.
I have often heard it said that the best way to protect a network is to put the hosts inside a vault, lock the door, post a guard and never connect the network to the Internet. Although this is a bit extreme, the concept is basic and understandable; access to a network is the means by which a security breach or attack occurs.
Remove the access and you remove the threat. Equally obvious is the fact that our networks need to be connected to the public Internet so there is the application for firewalls. By definition, firewalls should pass good traffic and block bad traffic.
This good and bad traffic is passing either to our firewall, from our firewall or through our firewall. In a passive or bridging firewall, the device is inserted into the network as a Layer 2 device meaning it is not routing packets. It typically has an IP address but only for the purpose of administration. Unlike a router, all packets that enter the passive firewall pass out of the firewall unless there are rules that specifically drop those packets.
In this book, we will be covering routing firewalls, although passive firewalls are created in a similar manner. Firewalls need rules to restrict traffic flow and fortunately these rules are organized in chains. The purpose of the chains is to determine at what point in the progression of a packet into or through the firewall a set of rules is applied. The three default chains are input, forward and output. There are also user created chains for organizational and load reducing purposes but they rely on the three default chains.
In summary, the user-defined chains do not see traffic or packets unless the packets are sent there by one of the three default chains. I will cover that in detail later in this chapter. The input chain is designed to protect the router itself. Consider the following diagram:. As you can see, this is a very typical placement of a firewall router at the gateway to the public Internet for a local area network. Packets coming from the LAN or from the WAN destined for the router itself will pass to the input chain, so that is the logical location for rules to protect the router.
This brings up an important detail about the operation of IP networks as it relates to the formation of packets. I am going to digress from firewalls for a moment and discuss packets. Packets are the messengers of the Internet, very similar to a letter you mail at the post office but not nearly that slow. These are often abbreviated as dst for destination and src for source. When Google gets the packets and wants to send it back with the information requested; it reverses the src and dst and you get what you requested.
Now, back to our example of input chain rules. Typically, the only packets that should be going to our router are either packets from communications, connections our router has initiated which we assume to be legitimate and safe , or packets representing us administering or configuring our routers.
This greatly narrows down the list of safe host IP addresses and makes creation of firewall rules much simpler. The easiest scheme to use when creating firewall rules is to allow what you determine to be good or safe traffic and then use wildcards to drop all other traffic. You could try and do the opposite and drop all the bad traffic, one protocol and port combination at a time, but to do so would require thousands or millions of rules and then you could never be sure you covered every possible threat.
Obviously, that is not a viable scheme so we will allow the good and drop everything else.. What protocols and ports will you use to administer the router?
Before we move on, it is necessary to examine the way firewall rules in any chain work. Rules are simply packet matchers. They define certain criteria to identify packets and then they perform some action on those packets. As you can see, nothing has yet been selected other than the chain.
This rule then matches all packets going to the router. In the next illustration, we have begun the process of narrowing down the packet matching criteria:. This rule now matches all types of packets but only if they are coming from src address our private LAN. Adding additional criteria will further narrow down the scope of this rule. Next, we must specify some action to be taken when a packet matches the rule.
This is done on the Action tab. This one rule, although very simplistic in nature, will allow any host in our LAN network of To create the drop rule, we simply create a second firewall rule matching all traffic by only selecting the input chain and nothing else on the General tab and then selecting an Action of drop. It is important to know that firewall rules like almost all rules in RouterOS are processed in order, top to bottom. Therefore if your accept rule is before your drop rule, everything works as expected.
If you put your drop rule first, well, you will lose access to your router. The router will not respond to pings from the public Internet and we will not be able to access the router from outside our LAN.
This is the first building block of a firewall. In addition, it is advisable to only allow the protocols and ports you will actually use. This is the most secure type of input firewall. If you follow the example above, you may notice that everything seems to work normally as it relates to accessing the router, however, this firewall will break other services the router provides to the LAN such as DNS if you are using the DNS caching facilities of RouterOS.
This is normal.
Learning firewalls can be very frustrating and complex unless you break them down into the building blocks that compose a firewall and teach these blocks in a progressive manner. Without allowing a new connection to be opened. They can be created by malformed or misbehaving software or a possible hacking attempt. Related connections are not new or established but are a part of an established connection.
Communication in networks is conducted using ports. Control the new connections and you control all other connections. These combinations of source and destination port are held constant for each connection between hosts. They are not new because they are created by a connection that has already been seen as new.
Connections Now we will bring in the next piece to the firewall puzzle. This is important. In this scenario. That would be an invalid packet. The easiest way to understand related connections is to think about them as what they are not. The rules to understand here and dedicate to memory are: I often abbreviate source as src and destination as dst. In addition to new connections and established connections. A connection is only new when it is initiated.
There are four types of connections: An invalid packet is one that does not belong to any know connection but does not create a new connection. Our data will be transmitted across these connections. A connection is established on the packets following the packet that creates the new connection. The second method is to filter based on connection state.
In addition. Figure 2 — Connections 1 In the preceding diagram. Following it is a new connection. The first rule allowed all traffic from.
We now have two parallel connections related to each other. If the connection is in a certain state. The third line begins as the first line with a new connection. The first method is to simply filter every packet coming into the router. Beginning with the first line. If it passes through our filter it is allowed. The fourth line begins as the first but ends with two invalid connections so can you guess what the next connection state would be?
If you answered new. To understand how these two methods work together and are used by a RouterOS firewall. The second line begins with an invalid connection. All packets following are a part of an established connection. A rule to accept all established connections. The router opens the new connection and the return is handled using an established connection rule.
This allows the ping to return from the host it was sent to. This is where connections state matchers can save the day. Add one more rule like it for related packets and this solves the problem.
The final result will be four rules on the input chain: The return connection when the ping packet reply arrives is now in the established state remember. It is not necessary to restrict new connections with firewall rules to the router because the only way a connection can be opened from the router is if we log into the router and generate a ping. This rule must be added above the drop rule and will allow a connection state of established.
Traffic flows both directions once your router opens that pipe. If a host on the LAN tries to ping the router. You can think about connections now as being a two way street or a pipe.
Obviously a related connection state rule works the same way and is also needed. This is a safe assumption. If the router tries to ping a host on the LAN. The second rule dropped everything else.
With connection state matchers. But now you ask. You may ask why. By adding a third rule we can allow our router to ping or for it to do DNS lookups by allowing that return path through a connection state rule. A rule to accept everything from the LAN network. We assume here that connections can not be created from the router unless we initiate them. One fix for this would be to write a new accept rule to accept ping packets from the WAN host you are pinging.
If you try this. In this statement. Connection state matchers are ideally suited for this job. There are several assumptions here:. Forward Chain As the input chain protects the router. You could add a rule to drop invalid connections but that would be redundant because rule 4 above drops everything else and that includes invalid connections. The host can now send data to the external host and the reverse flow will also be allowed.
Consider the following scenario. For instance you could allow all port 80 through the firewall and that helps a lot. For this purpose. Traffic to and from the hosts behind the firewall passes through the forward chain and so that is where we will place our rules.
The input firewall is now complete and you have thereby secured your router. So far. A rule to drop all other packets.. The first rule in our forward chain will allow customers on the LAN to create new connections through the firewall.
What about the scenario when your client wants to use SSH on port 22 or some other new application? That is where connection matchers can once again save the day and that is why I teach the forward chain using connection matchers. These rules will use matchers based on connection states and allow connections to be initiated only from the LAN.
By understanding the connection states we discussed previously. A rule to allow all related connections. Since all connection states begin as new connections. You want to create filter rules to allow protocols to pass through your firewall and drop hacking attempts. I am referring to all hosts behind the firewall as the clients. Add port Address lists are created to allow a single rule to.
This rule is less restrictive because we have already controlled new connections and secondarily restricted all other connections through this single control. Finally for good measure. The next rule will allow related connections. Note that only if the source address is on the LAN will the connection be allowed.
Address Lists The final piece of the basic firewall puzzle is the one that really simplifies our lives in the firewall world and that is the Address List. The third rule is similar to the second and allows established connections. If this is the second entry for a list. Without an Address List. Create a new address list entry using the plus sign for All of this may sound a bit confusing at this point until we tie it all together with some examples.
Once the address list entry is created. There you can click the plus sign to create a new entry and name it as you wish. With an address list based rule. In the address blank you can type an IP address. Example — The Basic Firewall For purposes of this example. To create a new Address List. A basic firewall will need two groups of rules on the input chain to protect the router itself and rules on the forward chain to protect the clients on the LAN. On the chain. Click the plus sign to create a new rule.
Rule 1: Click the IP button. Rule 2: These two rules drop invalid connections to and through the router.
This rule will allow anyone on your LAN to administer the router. Rule 4: Rule 3: This rule will allow our router to communicate with other hosts for services like ping or telnet. This rule will allow new connections from our LAN to pass through the router. Rule 6: This rule will drop all other hosts trying to access our router. On the advanced tab select the Src. For this rule. Rule 5: Rule 8: Rule 7: This rule will allow related connections through the router.
This rule will allow established connections through the router. The last rule drops all other connections through the router. This is our drop rule for the input chain. This makes everything work correctly.
Drops invalid connections on input and forward chains. If a new connection is created. Rule 9: The assumption is that we have already allowed everything that should be allowed so we drop everything else which is standard firewall philosophy. This is where we control the creation of new connections and restrict them only to connections that are sourced from our LAN.
Since we restricted new connections in step 6. The assumption is that we have already allowed everything that should be allowed so drop everything else. For Further Study: Now we allow related connections. This is our drop rule for the forward chain.
This example can be extended and serves only as the foundation of a stateful firewall. If you want to restrict certain protocols. Put that rule at or near the top of your list and LAN clients will not be able to initiate SSH connections outside the firewall.
Now we allow established connections. The default chains are: The most simple source NAT rule. Combined with connection states. Chapter 9 — NAT. Like all firewall functions. Once this is done. In addition to the firewall function. It allows functions such as masquerading. Once the switch is done. It also allows the opposite function. Since the rule is a source NAT rule. Like all NAT functions. This function allows a router with a single public IP address to function as an Internet gateway for a handful or even thousands of hosts or computers located behind the device on a private network.
NAT is the process of changing the original source IP. Network Address Translation In the previous chapter hopefully it was made clear the importance of understanding the source IP. NAT functions. In source NAT. That may be the desired scenario but in the case of a mail server or web server. To accomplish this. Doing this enables protection of the device with the firewall while still allowing the device to access the Internet via source NAT and masquerade. Destination NAT operates the same way.
The process occurs as follows: Since other mail servers will send packets to that IP we will then have to take those packets. In this case a returning packet will enter the router. In our example. This is necessary so that when the packet returns from the host it was sent to.
With the popularity of enterprises operating their own mail servers. The function can also be performed for destination port as well.
The first rule is the dstnat chain. Why would you want to do that? One application is an office that has a single public IP address. Once again. The same company operates a second private web server on a separate host server that runs a web server on port 80 for their partners. With only one public IP address and two web server machines that run their web service on port This allows us to use port 80 on the web server for a different function like a local intranet.
Their web server is hosted on the private network and operates on port 80 and they want to give the public access to their web site. The port change is made on the action tab. The answer lies in using destination NAT to change the destination port. This rule solves the issue. One of these controls is reverse DNS. Here is an example: Public IP of our router: The solution here is a source NAT rule. This would not be the normal behavior for a single source NAT rule with the action masquerade.
To summarize these processes. In the preceding example. The rule would match packets coming from In many scenarios this is acceptable but what if you add a secondary IP to the Internet facing interface on a different subnet and use that IP for a mail server located on the private network?
With the amount of unsolicited email SPAM that is processed every day by mail servers around the globe. The second rule is the dstnat chain. Getting back to our example. Consider an example. For whatever reason the decision is made to change upstream providers.
We will discuss caching DNS later in this book. Each of the actions you set for a NAT rule accomplishes a more complex function in the background. These pages fetched may be stored in memory or on disk for later serving to proxy clients. If we want this function to be applied without the knowledge of your clients or users and without intervention on their part. The second rule we need is a duplicate of the first with a protocol of UDP. This is where the redirect action can step in.
To summarize the difference between these two types of rules. Once configured. Think of redirect as a transparent NAT. Another example of using redirect is to create a transparent proxy. This speeds up network access. I have seen many very knowledgeable people use more complex packet matchers but this rule is all that is required and works well. This rule matches all traffic going out the Internet interface not local traffic and applies the masquerade action to it.
To accomplish this: