Home > Articles > Certification > Cisco Certification

Cisco ASA Filtering Botnet Traffic

One of the methods that can be used on the Cisco Adaptive Security Appliance (ASA) platform to avoid becoming a target of the bots subtype of malware attacks is to deploy its Botnet Traffic Filter. Sean Wilkins takes a look at how the Botnet Traffic Filter can be used to manually or automatically block these attacks from happening.
Like this article? We recommend

In the modern world, almost every business is connected to the Internet, and with this connection comes a giant potential security risk to the company. While it is possible for a business to not be on the Internet, very few have chosen to stay disconnected for a number of reasons.

One of the main threats that these businesses have to deal with is malware. In short, malware is a rogue program that attempts to take advantage of the weaknesses in a business' security. Some examples of malware include viruses, worms, trojans, and bots.

This article takes a look specifically at the bots subtype of malware. Bots are used to perform a number of different automated tasks that are controlled by a central entity.

A botnet is a group (typically a very large group) of bots that is controlled by a central attacker (or group of attackers). These bots can perform a number of tasks, from capturing traffic, to relaying attacker traffic to another bot, to performing large-scale Distributed Denial of Service (DDoS) attacks. Because of this, they are an important resource for attackers (and no business wants to become the prey of these attackers, either as a target or as a host of bots).

One of the methods that can be used on the Cisco Adaptive Security Appliance (ASA) platform to avoid becoming a target of these types of attacks is to deploy its Botnet Traffic Filter. This article takes a look at how the Botnet Traffic Filter can be used to manually or automatically block these attacks from happening.

Botnet Traffic Filter Concepts

The Botnet Traffic Filter works by monitoring the outbound connections of a network. If a connection is requested to a domain name or IP address (or IP address range) that is known to be bad, the traffic is flagged, and a message is sent to the syslog of the ASA.

It is also possible for this action to be escalated to the automatic dropping of the connection.

Static Threat Database

The first way that the filter can be configured is by using static entries, which can include domain names or IP addresses, or addresses that are automatically tagged as "good" (whitelisted) or "bad"(blacklisted), depending on the configuration.

All the traffic that is matched will be logged, and traffic that is tagged as "bad" can potentially be dropped when traffic to these destinations is initiated. Entries that are configured are inserted into a Domain Name System (DNS) host cache, which is then queried as traffic is sent through the ASA.

Dynamic Threat Database

The first thing to note is that the static database is really intended to be a supplement to the dynamic database. To expect to manually enter all potential blacklist entries for all the potential bad domain names and IP ranges is really an unrealistic goal. This is why Cisco offers a dynamic threat database.

This database is maintained by Cisco and can be downloaded onto the ASA. This database is received by the ASA and kept in running memory, specifically in the DNS reverse lookup cache.

There are a number of different threat traffic types that are included within these dynamic entries, including the following:

  • Ads: Include networks that are known to deliver banner ads, pop-ups, spyware, and adware
  • Data tracking: Includes networks that are associated with companies and websites that offer data tracking and metric services
  • Spyware: Includes networks that are known to distribute spyware, adware, greyware, and other advertising software
  • Malware: Includes networks that are known to use a variety of exploits to deliver adware, spyware, and other threats
  • Adult: Includes networks that are known to be associated with adult networks and services offering web hosting of adult content, advertising, content aggregation, registration, and billing
  • Bot and threat networks: Include networks that are known to host infected computer control software

Botnet Traffic Filter Operation

The static database functionality of the Botnet Traffic Filter works a little differently from the dynamic functionality. When a static entry is entered into the database, the ASA will wait one minute and perform a "normal" DNS lookup of the IP address matching the configured entry; the returned response will be entered into the ASA's DNS Host Cache.

This cache is then used to match traffic (by IP address) that is sent through the ASA (exactly how and what interfaces are inspected are configurable), both white and blacklisted entries are logged, and blacklisted entries can also be configured to be dropped.

The application of the dynamic database functionality of the Botnet Traffic Filter depends on how exactly it is configured; to get the most out of the capabilities of the feature, the ASA will be configured to perform DNS inspection along with the operation of the Botnet Traffic Filter.

If DNS inspection is not enabled, the filter will provide protection only against static database blacklist entries (logging and dropping) and dynamic database entries that consist of an IP address or IP address range. It will not filter any traffic that is entered in the dynamic database using a host or domain name.

When DNS inspection is enabled, the filter will provide the most amount of protection by inspecting dynamic entries that are entered in IP address (or IP network) form and those that are entered as host or domain names.

When using the dynamic (and potentially static) capabilities, the filter will monitor the operation of the DNS inspection feature. When a DNS request is transmitted by an internal host, the ASA will match the DNS information against the entries that exist within the dynamic database. If a match is found, an entry will be added to the ASA's DNS Reverse Lookup Cache (as an IP address).

If the internal host continues to send traffic to the inquired destination, it will be matched against the DNS Reverse Lookup Cache (and the DNS Host Cache) and the traffic will be logged and potentially dropped before reaching the destination.

Summary

When put into full operation, the functionality of the Botnet Traffic Filter can certainly be quite effective, along with a larger network security plan to maintain a high level of security within a business' internal network.

Those hosts that have been infected by malicious software will be found by monitoring the log of the filter before any potential future (and external) harm can be done.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT 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 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 InformIT. 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.informit.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