Configuring cisco asa and pix firewalls part3
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Configuring cisco asa and pix firewalls part3 Configuring cisco asa and pix firewalls part3 Document Transcript

  • Configuring Cisco ASA and PIX Firewalls-Part2 5. Working With Objects Firewall Builder is based on the concept of objects. There are a variety of different object types used to define IP objects that can be used as the Source and Destination in your firewall rules. Two of the most common IP objects used in firewall rules are Networks and Addresses. Network Objects To create the example Network object representing the internal 10.10.10.0/24 network shown in the diagram on the previous page, go to the object tree on the left side of the screen and double-click the folder labeled Objects to expand it. Right click on the folder called Networks and select “New Network”. This creates a new network object. In the lower portion of your screen, called the Editor Panel, you can modify the properties of this new network object. Change the object name to something matching the function. In this example we name it “Internal Network” to represent the network connected to our "inside" interface. The address is set to 10.10.10.0 and the netmask is 255.255.255.0. Figure 13. New Network Object Note When editing the attributes of an object there is no Apply or Submit button. Once you edit an attribute, as soon as you move away from the field you were editing the change immediately takes effect. Address Objects To create an object representing a single IP address, similar to the host parameter in
  • a Cisco access list, go to the object tree, right-click on the Addresses folder, and select "New Address". In the Editor Panel change the name of the new address object to something that reflects its function, for example “POP3 Server”. Also set the IP address. Figure 14. New Address Object You may have noticed that we did not create any objects for the TCP services like HTTP and SSH needed for the firewall object rules shown in the example. This is because Firewall Builder comes with hundreds of predefined objects for commonly used objects like TCP services. 6. Configuring Policy Rules (Access Lists) After you have created a firewall object and network objects you can start to configure the firewall's rules. When you create a firewall object, for example asa-1 from our previous example, it is opened automatically in the object tree and its Policy object is opened in the main window for editing. The Policy object is where access list rules are configured. To add a new rule to the Policy, click on the green icon at the top left of the main window. This creates a new rule with default values set to deny all. Figure 15. Default Rule Every rule includes the following sections: Source - this can be one or more IP objects. The default value is Any which is the same as the "any" parameter in a Cisco access list that matches all IP addresses. Destination - this can be one or more IP objects. The default value is Any which is the same as the "any" parameter in a Cisco access list that matches all IP addresses. Service - this can be one or more Service objects. Example services include
  • TCP and UDP protocols like HTTP and DNS. The default value is Any which matches any IP service and is the same as the "ip" parameter in Cisco access lists. Interface - this can be one or more interfaces configured on the firewall (router) object. The default value is All which means the rule will be applied as an access list to all configured interfaces. Direction - options are Inbound, Outbound, and Both. This defines whether the resulting access-group will be applied to interfaces as "in" or "out". Both will generate an identical rule for "in" and "out". The default value is Both. Action - options are Accept and Deny. This matches the Cisco access list parameters "permit" and "deny". The default value is Deny. Options - options are Logging On and Logging Off. Setting Logging On matches the Cisco access list parameter "log". The default value is Logging On. Configuring a Rule In the example below, the fields in the rule will be set to the values that match the first rule from our example scenario (scenario rules shown in figure below). This first rule controls SSH access to the firewall itself. Figure 16. Scenario Rules Setting the Source To set the Source of a rule, drag-and-drop at least one IP object from the tree to the Source field of your rule. For example, drag the Network object called Internal Network that you created earlier to the Source column of the rule as shown below. Figure 17. Setting the Source After you drop the network object into the rule the Source field will change from Any to Internal Network. Figure 18. After Source is Set
  • Note You can have more than one IP object in the Source and Destination fields. When Firewall Builder generates the Cisco command line access lists it will automatically split the rule into multiple lines if necessary. Setting the Destination Setting the Destination is exactly the same as setting the Source, except you drag-and-drop IP objects in to the Destination field of the rule. For our first example rule we want the Destination to be the "inside" interface of the firewall object. Drag-and-drop the Ethernet0/1 object from the object tree to the Destination column. Figure 19. Setting the Destination After you drop the interface object into the rule the Destination field will change from Any to "inside", the label of the Ethernet0/1 interface. Figure 20. After Destination is Set Setting the Service Firewall Builder comes with hundreds of predefined objects including Service objects for almost all standard protocols. To access these objects switch to the Standard library by selecting it from the drop down at the top of the Object tree window. Figure 21. Switching Libraries
  • Services are located in the Services folder. In this rule we want to set the service to SSH, so you would navigate to the SSH service by opening the Services folder, then opening the TCP folder and scrolling down until you find the "ssh" object. Once you find the ssh object, drag-and-drop from the tree on the left in to the Service section of the rule in the Rules window. Figure 22. Setting the Service Note To switch back to the User library, which contains objects you have created, click on the drop down menu that says Standard and select User from the list of libraries. Setting the Interface If desired, set the Interface for the rule by dragging-and-dropping an interface object from the firewall (router) object to the Interface section of the rule. This will explicitly define which interface on the router that the access list will be applied to as an "access-group". Figure 23. Setting the Interface
  • Setting the Direction The direction of the rule is based on the traffic you want to filter. Traffic coming in to an interface should have the rule Direction set to Inbound and traffic going out of an interface should have the rule Direction set to Outbound. In our example the direction of the rule will be Inbound since it is controlling access to the firewall itself on the "inside" interface. Right-click and set the direction to Inbound. The Direction, Network Zone and the Interface settings in a rule will determine which interfaces should have this rule applied. Note A word about Inbound vs. Outbound access lists: Older PIX versions did not support outbound access lists on interfaces, so by default Firewall Builder emulates this behavior. This means if you create an outbound rule on an interface, Firewall Builder will convert that to inbound rules on all other interfaces. You can change this behavior by editing the Firewall Settings for the firewall object and clicking the checkbox next to "Generate outbound ACLs". Setting the Action The action controls whether traffic matching the rule should be permitted or denied. Remember, all Cisco access lists have an implicit deny at the end of the list, so any traffic that has not matched a rule that permits the traffic will be dropped. Right-click and set the action to "Accept" to allow the SSH traffic from the local network to the firewall. Setting the Options Logging for rule matches is set in the Options section. By default logging is turned on. To turn logging off, right-click in the Options section and select Logging Off. Example of a Complete Rule The following is the first rule from our example which allows traffic from the internal network to the firewall's inside interface that has a traffic type of SSH. Figure 24. New Rule with Fields Set
  • 6.1. Additional Tips For Working with Rules Adding a Rule To add a new rule click the icon at the top of the Rules Editor window. This inserts a new rule above the current rule. To add a new rule below the current rule right-click on a rule and select "Add New Rule Below". Figure 25. Adding Rules Copy-and-Paste In addition to drag-and-drop you can also copy-and-paste objects. For example, you can right-click on the Internal Network object in the first rule and select Copy. Navigate to the Source section of the new rule you just created and right-click and select Paste. Using Filters to Find Objects Filters provide a way to quickly find objects in the tree without having to open multiple folders and scroll. For example, if you wanted to use the POP3 protocol in a rule you could use the filter to find it. The POP3 protocol object is located in the Standard library, so select it from the dropdown menu at the top of the Object Window. Type pop3 in to the filter field. This will display all objects in the current library that contain pop3. Figure 26. Using Filter to Find Objects Note After you are done with the filtered object, clear the filter field by clicking the X to
  • the right of the input box and then switch back to the User library by selecting it in the dropdown menu at the top of the object panel. Example of Completed Rules For our example we needed to create two firewall rules. The completed firewalll rules are shown in the diagram below. Figure 27. Two Rules More… Cisco Guide: Migration of Cisco PIX 500 Series to Cisco ASA 5500 Series Cisco PIX Firewall Basics