Home > Articles

Network Components

  • Print
  • + Share This
This chapter is from the book

Internal Security

After traffic has passed through the perimeter, the packets need to be properly routed. In some instances, only internal routing occurs because the traffic is strictly internal and doesn’t need to leave the organization. In this case, devices are used that do not route traffic or that prevent traffic from leaving a subnet. Devices that perform this role include routers, switches, and bridges.

Routers

Routers operate at the network layer of the OSI model. They receive information from a host and forward that information to its destination on the network or the Internet. Routers maintain tables that are checked each time a packet needs to be redirected from one interface to another. The tables inside the router help speed up request resolution so that packets can reach their destination more quickly. The routes can be added manually to the routing table or can be updated automatically using the following protocols:

  • Routing Information Protocol (RIP/RIPv2)

  • Interior Gateway Routing Protocol (IGRP)

  • Enhanced Interior Gateway Routing Protocol (EIGRP)

  • Open Shortest Path First (OSPF)

  • Border Gateway Protocol (BGP)

  • Exterior Gateway Protocol (EGP)

  • Intermediate System-to-Intermediate System (IS-IS)

Although router placement is primarily determined by the need to segment different networks or subnets, routers also have some good security features. One of the best features of a router is its capability to filter packets by source address, destination address, protocol, or port. These filters are actually access control lists (ACLs).

Part I, “Threats, Attacks, and Vulnerabilities,” describes attacks such as IP spoofing and covers Domain 1 of the Security+ exam. Basic Internet routing is based on the destination IP address, so a router with a default configuration forwards packets based only on the destination IP address. In IP spoofing, an attacker gains unauthorized access to a network by making it appear (by faking the IP address) that traffic has come from a trusted source.

Because routers are the lifeblood of the network, it is important to properly secure them. The security that is configured when setting up and managing routers can make the difference between keeping data secure and providing an open invitation to hackers. The following are general recommendations for router security:

  • Create and maintain a written router security policy. The policy should identify who is allowed to log into the router and who is allowed to configure and update it. The policy also should outline the logging and management practices.

  • Comment and organize offline master editions of your router configuration files. Keep the offline copies of all router configurations in sync with the actual configurations running on the routers.

  • Implement access lists that allow only the protocols, ports, and IP addresses that network users and services require. Deny everything else.

  • Test the security of your routers regularly, especially after any major configuration changes.

Keep in mind that, no matter how secure your routing protocol is, if you never change the default password on the router, you leave yourself wide open to attacks. At the opposite end of the spectrum, a router that is too tightly locked down can turn a functional network into a completely isolated network that does not allow access to anyone.

Switches

Switches are the most common choice when it comes to connecting desktops to the wiring closet. Switches generally operate at the data link layer (Layer 2) of the OSI model. Their packet-forwarding decisions are based on Media Access Control (MAC) addresses. Switches allow LANs to be segmented, thus increasing the amount of bandwidth that goes to each device. Each segment is a separate collision domain, but all segments are in the same broadcast domain. Here are the basic functions of a switch:

  • Filtering and forwarding frames

  • Learning MAC addresses

  • Preventing loops

Managed switches are configurable. You can implement sound security with your switches similarly to configuring security on a firewall or a router. Managed switches allow control over network traffic and who has access to the network. In general, you do not want to deploy managed switches using their default configuration. The default configuration often does not provide the most secure network design. In such cases, these switches require no Layer 2 functionality.

A design that properly segments the network can be accomplished using VLANs. VLANs provide a way to limit broadcast traffic in a switched network. This creates a boundary and, in essence, creates multiple, isolated LANs on one switch. VLANs are a logical separation of a physical network and often combine Layer 2 and Layer 3 switches. Layer 3 switches can best be described as routers with fast forwarding done through hardware. Layer 3 switches can perform some of the same functions as routers and offer more flexibility than Layer 2 switches.

Designing the network the proper way from the start is important to ensure that the network is stable, reliable, and scalable. Physical and virtual security controls must be in place. Locate switches in a physically secure area, if possible. Be sure that strong authentication and password policies are in place to secure access to the operating system and configuration files.

Protections

Port security is a Layer 2 traffic control feature on switches. It enables individual switch ports to be configured to allow only a specified number of source MAC addresses to come in through the port. Its primary use is to keep two or three users from sharing a single access port. You can use the port security feature to restrict input to an interface by limiting and identifying MAC addresses of the workstations that are allowed to access the port. When you assign secure MAC addresses to a secure port, the port does not forward packets with source addresses outside the group of defined addresses. If you limit the number of secure MAC addresses to one and assign a single secure MAC address, the workstation attached to that port is assured the full bandwidth of the port. By default, a port security violation forces the interface into the error-disabled state. Port security can be configured to take one of three actions upon detecting a violation. In addition to using the default shutdown mode, you can set protect mode or restrict mode. In protect mode, frames from MAC addresses other than the allowed addresses are dropped. Restrict mode is similar to protect mode, but it generates a syslog message and increases the violation counter.

A flood guard is an advanced firewall guard feature used to control network activity associated with DoS attacks and distributed denial-of-service (DDoS) attacks.

For example, in Cisco firewalls, the floodguard command is enabled by default and the firewall actively reclaims TCP user resources when an inbound or outbound authorization connection is being attacked. Flood guards are available as either standalone devices or firewall components.

Bridges

Bridges are often used when two different network types need to be accessed. Bridges provide some network layer functions, such as route discovery, as well as forwarding at the data link layer. They forward packets only between networks that are destined for the other network. Several types of bridges exist:

  • Transparent basic bridge: Acts similarly to a repeater. It merely stores traffic until it can move on.

  • Source routing bridge: Interprets the routing information field (RIF) in the LAN frame header.

  • Transparent learning bridge: Locates the routing location using the source and destination addresses in its routing table. As new destination addresses are found, they are added to the routing table.

  • Transparent spanning bridge: Contains a subnet of the full topology for creating a loop-free operation.

Looping problems can occur when a site uses two or more bridges in parallel between two LANs to increase the reliability of the network. A major feature in Layer 2 devices is Spanning Tree Protocol (STP), a link-management protocol that provides path redundancy while preventing undesirable loops in the network. Multiple active paths between stations cause loops in the network. When loops occur, some devices see stations that appear on both sides of the device. This condition confuses the forwarding algorithm and allows duplicate frames to be forwarded. This situation can occur in bridges as well as Layer 2 switches.

A bridge loop occurs when data units can travel from a first LAN segment to a second LAN segment through more than one path. To eliminate bridge loops, existing bridge devices typically employ a technique referred to as the spanning tree algorithm. The spanning tree algorithm is implemented by bridges interchanging special messages known as bridge protocol data units (BPDUs). The STP loop guard feature provides additional protection against STP loops.

An STP loop is created when an STP blocking port in a redundant topology erroneously transitions to the forwarding state. This usually happens because one of the ports of a physically redundant topology no longer receives STP BPDUs. In its operation, STP relies on continuous reception or transmission of BPDUs, based on the port role. The loop guard feature makes additional checks. If BPDUs are not received on a nondesignated port and loop guard is enabled, that port is moved into the STP loop-inconsistent blocking state instead of the listening/learning/forwarding state. Without the loop guard feature, the port assumes the designated port role. The port then moves to the STP forwarding state and creates a loop.

  • + Share This
  • 🔖 Save To Your Account

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Pearson IT Certification products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.pearsonitcertification.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020