Network Defense Fundamentals And Protocols Pdf

network defense fundamentals and protocols pdf

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Certified Network Defender CND is a vendor-neutral, hands-on, instructor-led comprehensive network security certification training program.

Network Defense Fundamentals And Protocols Ec Council Press

You also have to be aware of security risks and controls available in the public switched telephone networks PSTN infrastructure because PSTNs are often used for computer communications. This section of the chapter introduces the security concepts applicable to physical devices, network topologies, and storage media.

A firewall is a hardware device or software application installed on the borderline of secured networks to examine and control incoming and outgoing network communications. As the first line of network defense, firewalls provide protection from outside attacks, but they have no control over attacks from within the corporate network. Some firewalls also block traffic and services that are actually legitimate.

Know that a firewall is a hardware or software system designed to protect one network from another network, and be familiar with the various types of firewalls. Because network security is concentrated on configuring the firewall, or at least is built around it, a compromised firewall can mean a disaster for a network. For smaller companies, though, a firewall represents the best investment of time and money. All things considered, a firewall is as indispensable as the Internet itself; however, you should not rely on it exclusively for top-to-bottom network protection.

Increasingly, companies are also deploying firewalls outside the edges of networks, as well as between network segments and even on individual machines, where justified.

Firewall architectures include the following:. Packet-filtering architecture involves checking network traffic for source and destination addresses, source and destination port numbers, and protocol types. Packet filtering allows an administrator to exclude traffic based on its source and destination addresses, and, depending on the device, it can also exclude traffic aimed at specific protocols and ports or traffic that is sent to or from particular addresses.

Most quality routers not just firewalls have packet-filtering functionality built in. Devices made by Cisco Systems, the undisputed leader in the area of network devices in general, employ access lists provided as a feature of the Internetwork Operating System IOS.

Only extended lists allow you to check for all the previously listed characteristics and include some other conditions, such as secondary connections. These access lists can be applied to different interfaces to screen network traffic in both directions or in either direction on each interface.

You can apply an access list filter to the external interface so the router will discard prohibited packets before it has to spend CPU time on making a routing decision. All packets that are not explicitly permitted are effectively rejected. Packet-filtering solutions are considered generally less secure than circuit-level architectures because they still allow packets inside the network regardless of the communication pattern within the session. Thisopens the system to denial-of-services DoS attacks buffer overflow exploits in "allowed" applications on target machines, connections exhaustion, and so on.

This monitoring, performed on the Session layer layer 5 of the OSI model, is done to determine whether a requested session is legitimate. The firewall ensures that these session establishment packets occur only when prescribed.

It also verifies the validity of the sequence numbers used in TCP to reassemble packets in the correct order, as shown in Figure 3. Figure 3. Popular attacks, such as DoS, are often launched when an attacker begins the TCP three-step handshake sequence with a SYN packet and thereby begins to establish a connection that is never completed. Instead, the attacker emits another SYN packet and initiates another connection that is also never completed when repeated thousands of times, it causes problems.

This attack, called a SYN flood , forces a victim system to use up one of its finite number of connections for each connection the initiator opens. Because these requests arrive so quickly, the victim system has no time to free dangling, incomplete connections before all its resources are consumed.

However, a massive number of connection attempts can occur during the normal default timeout period, thereby exhausting system resources and making the system unavailable for legitimate users. These attacks are detected and prevented in circuit-level architectures where a security device discards suspicious requests. If you receive 2, SYN connection requests per minute from a single host, you should become suspicious.

Security devices can also be configured to do some or all of the following:. Legitimate traffic from that address will be blocked as well. Microsoft is focusing more efforts on security; however, many of the new security features are not well known and are disabled in default configurations.

In fact, some of these techniques are not unique to firewalls and borderline devices, but instead should be considered for company-wide deployment. This can enable an attacker to map your network. If it does, a service is running on the target port of the machine.

Different services run on default ports. Port scanning programs check ports and use responses from these ports to guess which services are running on a machine. This is known as fingerprinting. These programs can be used to find and close security holes on your network by simulating attacker reconnaissance and exploit behavior. Do not use them without prior consent and knowledge of your network administrator. These reports sometimes reveal important email infrastructure elements, such as IP addresses and hostnames.

Spammers use a form of email probing for different purposes, as noted in Chapter 2. These DoS attacks are not application specific and can be prevented by a firewall. Buffer overruns occur when attackers intentionally send more data than an application is designed to handle, causing the application to crash.

A firewall cannot prevent this type of attack without preventing all communication with a particular application. This type of attack can be prevented by ensuring that applications run on your network have been tested against this type of attack. Potentially, the attacker not only escapes liability, but also appears to be a trusted source who has permission to access the system. Authentication methods, rath.

A firewall really can't do much against this technique, but applications aimed at detecting network nodes running in promiscuous mode can be used. A Trojan horse is an application that is hidden in some other type of content, such as a legitimate program. It can be used to create a new, secret account called a back door , or it can be used to run spyware , which collects user keystrokes for analysis. Trojan horses can also be used to infect and control affected systems, destroy and expose valuable company information, or use your systems as launching pads for further attacks from the inside.

After an internal system is infected, a firewall is not very effective protection, although it can prevent certain types of traffic from flowing between the attacker and the infected host or between the infected host and other potential victims. Some Application-layer layer 7 firewalls offer content filtering, which can help keep malicious Java applets and ActiveX controls out of your network. All DNS servers must be configured to refuse such a listing if the request does not originate from a preconfigured DNS replication partner.

If a DNS software vendor does not allow disabling of the ls command, consider implementing a separate DNS server for publicly accessible services, such as those located in the demilitarized zone DMZ , or switch software vendors.

Some reconnaissance probes can reveal more than enough information for an attacker to proceed with his plan. If a potential attacker doesn't know about your infrastructure and cannot probe it, chances are you are safe, at least until the next attacker tries.

You cannot guarantee that your ISP will monitor its network for such activity and prosecute port scanners and ping sweepers. Therefore, you want your firewall to catch these reconnaissance attempts, log the source information, and alert administrators on-the-fly.

Ping sweeps are simple to protect against, but you should be aware that ICMP requests might be rejected or discarded and that this difference is important to attackers. Actively rejected ICMP echo requests mean that the target host is alive, which gives the attacker information. To protect against this probe, a firewall needs to discard the packet silently so the attacker's ICMP requests appear to be sent to an unused IP address. The same goes for port scanning: a decent firewall detects a port scan in progress and rejects further requests from the source IP address, sending a real-time alert to the administrator.

Attackers Look for Vulnerable Systems Many attackers look for vulnerable systems, not caring who owns them. These attackers are seldom interested in uncooperative systems, but they shouldn't be the basis of your security policy. A free, limited version is available that is still very useful for security configuration and verification purposes. In addition to vulnerability walkthroughs, you can look through security tutorials on a host of topics, get privacy protection information, and download several tools.

Be cautious installing the tools, though; be sure you are not installing a Trojan horse or other malware. Many times, attacks are daisy-chained in a bid to get as much information or cause as much damage as possible. For example, an attack can begin with a ping sweep and when a host replies, a port scan is launched. The port scan can find the SMTP email port. Next, an email probe is sent to reveal information about the type of email software the server is running, resulting in a non-delivery receipt NDR reply.

Then, the attacker can test that specific email server for known vulnerabilities to see whether it is patched or can be exploited. He uses the email's headers and notes the message's path from the very first communication point until it reached him.

Next, the attacker uses PING , nslookup , and whois to find the ISP's domain name, address, and administrative contacts, as well as which name servers are responsible for that domain.

Using a ping sweep to locate active hosts and then port scanning to detect services on those active boxes, he launches attacks against vulnerable applications. If the ISP uses descriptive names in its DNS, an attacker can learn about physical connection types and the estimated bandwidth of the target. In a worst case scenario, if crashing or breaking into that machine is not possible, social engineering can still work for the attacker.

A good firewall also prevents non-application-specific denial-of-service attacks and, in some cases, even provides content filtering if it is an Application-level gateway. An Application-level gateway is known as a proxy , and it functions on the highest layer of the OSI model: the Application layer. A proxy server basically inserts itself between an internal client inside the network perimeter and an external server outside the network perimeter for the express purpose of monitoring and sanitizing external communications.

For example, a proxy can remove references to internal or private IP addresses from client communications before emitting them onto a public network segment, thereby hiding information about network internals and details from outsiders. Therefore, user access can be controlled on an individual basis, group policies can be applied, content types can be restricted, and so on. The higher up the OSI model that a proxy can operate, the more controls that can be implemented; however, there might be some costs in either performance or flexibility.

Some applications will not run properly because the protocols they use can't be proxied , or such applications might need to be specially configured to operate in the presence of a proxy server such implementations are called proxyable or proxy aware when they can be made to work with a proxy server. The fourth type of firewall architecture, stateful inspection , combines the aspects of the three basic architectures explained in the previous sections.

Stateful inspection firewalls not only examine packets at the Network layer, but also gather information about the packet's communications session from all layers to determine whether a packet is valid in the context in which it is received.

For example, when a communications session is opened, the session is recorded in a state table. Subsequent session packets are checked against this state table to verify that they are valid in the context of the session. A packet that is already part of a valid session does not have to be compared to all the rules, which speeds up processing.

Packets that do not make sense in the context of an open session can be discarded. Likewise, packets that attempt to exercise questionable or unwanted commands or activities can be blocked, and questionable patterns of activity attempts at dangling synchronization, invalid segment sizes, and so forth can be discarded.

This prevents potential attacks from getting underway or denials of service from succeeding, but requires complex custom configurations to work. Granted, firewalls residing higher up the OSI model can perform the same inspections that lower-level implementations can, but they are more complex to write leaving the potential for overlooked back doors and lots of bugs , more complicated to maintain, and less complicated to attack as a result of the first two.

However, providing that the software was written correctly and is deployed and maintained correctly, this provides the best security level.

CND Module 01 Computer Network and Defense Fundamentals.pdf

Network security is any activity designed to protect the usability and integrity of your network and data. If you're looking to increase protection for your remote employees so they can work from any device, at any time, from any location, get started with the Cisco Secure Remote Worker solution. Network security combines multiple layers of defenses at the edge and in the network. Each network security layer implements policies and controls. Authorized users gain access to network resources, but malicious actors are blocked from carrying out exploits and threats.


Computer Network and Defense Fundamentals. TCP/IP Model. CND. TCP/IP model is a framework for the Internet Protocol suite of computer network protocols​.


EC-Council Certified Network Defender (CND)

Inventory and Control of Hardware Assets. Inventory and Control of Software Assets. Continuous Vulnerability Management.

You also have to be aware of security risks and controls available in the public switched telephone networks PSTN infrastructure because PSTNs are often used for computer communications. This section of the chapter introduces the security concepts applicable to physical devices, network topologies, and storage media. A firewall is a hardware device or software application installed on the borderline of secured networks to examine and control incoming and outgoing network communications. As the first line of network defense, firewalls provide protection from outside attacks, but they have no control over attacks from within the corporate network.

Reading for Week 1 :. This is a simplified view of things, and while some signature schemes look similar to some public key encryption where the decryption algorithm is used for singing and the encryption algorithm for signature verification, but this usage of public key encryption can, and indeed often does, lead to a completely insecure signature scheme. The attack described in the man-in-the-middle subsection is called a malleability attack.

Network Defense and Countermeasures: Principles and Practices, 3rd Edition

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Certified Network Defender CND is a vendor-neutral, hands-on, instructor-led comprehensive network security certification training program. It is a skills-based, lab intensive program based on a job-task analysis and cybersecurity education framework presented by the National Initiative of Cybersecurity Education NICE. The course is designed and developed after extensive market research and surveys.

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The Certified Network Defender CND certification program focuses on creating Network Administrators who are trained on protecting, detecting and responding to the threats on the network. Network administrators are usually familiar with network components, traffic, performance and utilization, network topology, location of each system, security policy, etc. A CND will get the fundamental understanding of the true construct of data transfer, network technologies, software technologies so that the they understand how networks operate, understand what software is automating and how to analyze the subject material. In addition, network defense fundamentals, the application of network security controls, protocols, perimeter appliances, secure IDS, VPN and firewall configuration, intricacies of network traffic signature, analysis and vulnerability scanning are also covered which will help the Network Administrator design greater network security policies and successful incident response plans.. CND is a skills-based, lab intensive network security program based on a job-task analysis and cybersecurity education framework presented by the National Initiative of Cybersecurity Education NICE.


Module Computer Network and Defense Fundamentals. ▫ Network Module Network Security Controls, Protocols, and Devices. ▫ Fundamental.


The 20 CIS Controls & Resources

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