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How NetFilter Works
NetFilter, or more commonly known by the name of the manipulation utility, iptables, works, on the surface, similarly to the ipchains firewall code of earlier Linux kernels
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How the Linksys Router/Firewall Works
Most Linksys routers/firewalls rely on simple NAT routing and basic port filtering to control the flow of traffic through the router.
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How the PIX/ASA Firewall Works
Note With the implementation of the PIX and ASA software starting with version 7.0, many of the features and functionality of the firewall were changed dramatically.
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Internet Control Message Protocol (ICMP)
TCP and UDP exist primarily to deliver upper-layer data across a network. Whether connection oriented or connectionless, fundamentally the process of delivering the data is the same
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Internet Protocol (IP)
In many ways, IP is the network. IP is a connectionless protocol that provides for the delivery of data to logically addressed hosts anywhere on the network
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Intrusion Detection and Prevention
Because network traffic must cross the firewall to reach the end systems, the firewall has also become a point where the inspection of this traffic is appropriate.
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IP Services
When we talk about IP services, we refer to the applications, protocols, and services that not only use IP themselves, but also provide data to be used by other IP protocols.
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Limitations of Application Proxy Firewalls
Because of how effective application proxies can be at filtering traffic, one might wonder why everyone does not use an application proxy firewall.
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Linksys Broadband Routers/Firewalls
Linksys makes a number of broadband routers (with basic firewall functionality) and broadband firewalls
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Linksys Checklist
Step 1. Step 2. Obtain the connection information required by your ISP. Plug the router into the service provider device or network jack using the external/WAN interface of the router
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Linksys Requirements
Most Linksys routers have an extremely small requirements list. Because the assumption is that the router will be connected to a small or home network that lacks any kind of DHCP server
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Logging and Log-Analysis Tools
Most firewalls can log events related to traffic that has been permitted or denied. Unfortunately, the sheer volume of data from even a moderately sized environment can quickly become unmanageable.
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Maintaining the Underlying Platform
As with any device on the network, firewalls run software (whether it is embedded in an application-specific integrated circuit [ASIC] or runs from Flash memory or runs from a disk file system) to be able to perform their functions.
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Management Access
Management Access Control of access to the management interface of network infrastructure devices is critical. Network devices such as routers, switches, intrusion detection sensors
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Microsoft ISA Server 2004 Firewall phần 1
Microsoft ISA Server 2004 is a hybrid stateful packet-inspecting, circuit-filtering, and application layer proxy firewall.
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Microsoft ISA Server 2004 Firewall phần 2
SecureNAT Client The SecureNAT client is effectively any device that attempts to communicate through the ISA Server 2004 firewall without being configured as one of the other firewall types
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Microsoft ISA Server 2004 Firewall phần 3
To perform remote administration of ISA Server 2004 firewalls using the management console, the management workstation must be added to the Enterprise Remote Management Computers (to manage all firewalls in the enterprise)
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Microsoft ISA Server 2004 Firewall phần 4
Publishing Internal Resources Publishing internal resources follows largely the same process as creating an access rule. It is a wizard-driven process
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NetFilter Checklist
NetFilter Checklist Building a NetFilterbased firewall is not difficult. End users interested in setting up their own NetFilter firewall can use the system to be used as the firewall. Install additional network interfaces (minimum number of required interfaces is two)
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Network Address Translation (NAT)
NAT was developed to address a couple of concerns. First, the number of public IP addresses available on the Internet was becoming depleted
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Open and Closed Source Firewalls
You can find a wide variety of firewalls available on the market today. Some are open source, such as Linux's IPTables, OpenBSD's pf
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Performing Application Filtering
Application filtering is one of the most difficult types of filtering that firewalls perform, because it requires the firewall to process the data at the application layer (Layer 7) of the OSI model
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PIX/ASA Checklist
As with configuring any firewall, administrators should develop a checklist that they can use during the installation and implementation of the PIX/ASA firewall in the network
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PIX/ASA Features
The PIX/ASA is a powerful stateful packet-inspection firewall with some basic application-inspection capabilities.
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Protocols, Services, and Applications
Protocols, Services, and Applications As mentioned, TCP/IP provides a mechanism to allow systems to communicate with each other across a network.
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Proxy Server Functionality
Act as an intermediary between hosts Cache data to reduce the time and external bandwidth required to service requests
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Security Policies
Consequently, a firewall is only as effective as the firewall security policy (as opposed to the enterprise security policy) that dictates how the firewall will be used
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Security-Testing Tools
No discussion of firewall and security tools is complete without a brief discussion regarding security-testing tools.
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Single-Firewall Architectures
There are two predominant firewall architectures, the single-firewall and dual-firewall architectures.
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The Firewall System
To paraphrase Shrek, the network perimeter is like an onion; it has lots of layers.
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