Home > Articles > Operating Systems, Server > Solaris

  • Print
  • + Share This
Like this article? We recommend

ARP

The Address Resolution Protocol (ARP) is used to map 32-bit IPv4 addresses to the address scheme used by the data-link layer. The data-link layer, sometimes referred to as the network link layer, consists of the operating system device driver and corresponding network interface card. This layer is responsible for dealing with the physical transport media. Sun network devices use a system-wide hardware address, sometimes referred to as the Media Access Control (MAC) address. This means that a Sun system with multiple Ethernet interfaces will, by default, have the same hardware address for each interface.

A Sun Quad FastEthernet_ card has a unique hardware address assigned to each of its four interfaces. It is also possible to configure the card to use the hardware address from the cards programmable read only memory (PROM). Refer to the Sun Quad FastEthernet card documentation for more information.

It should be noted that many operating systems, including the Solaris OE, allow the hardware or MAC address, of a network interface, to be defined through software. By explicitly setting the hardware address of a network interface in software, the vendor-defined hardware address will be overridden.

ARP is often referred to as a dynamic protocol. This is due to the fact that its operation occurs automatically. The protocol works in the background, without concern to the application user or even the network administrator. It is this dynamic nature of ARP that causes security issues.

For the purposes of this discussion, we use Ethernet (IEEE 802.3). Token ring and Fiber Distributed Data Interface (FDDI) have similar schemes.

ARP operates by broadcasting an address request and collecting the response to create its map of addresses. The hardware addresses are only needed for hosts on the local network. At the lowest level, the Ethernet driver needs the hardware address of the remote system, to send it a packet. When it does not have that address, it broadcasts a request for the missing address. This request, called an ARP request, contains the IP address of the host in question and is sent to all systems on the local network. A system might respond with a reply, called an ARP reply, which contains the host IP address and hardware address. The received response is used to build a table of IP addresses and the corresponding hardware addresses.

In the Solaris OE kernel, there are two tables that maintain the addresses. One table, maintained by the ARP layer, is called the ARP cache. It provides a layer of efficiency to the protocol. For instance, when a hardware address is requested by the IP layer, the ARP cache is checked first. If the address information does not exist in the local cache, an ARP request is sent, and the corresponding reply is processed. The Solaris OE also adds unsolicited address information to the ARP cache. These unsolicited address entries are special because they were not directly requested. These unsolicited entries are kept in case the IP layer requests them. After a period of time, all unsolicited entries are deleted from the cache. The default timeout value for unsolicited entries is five minutes and can be adjusted.

The other table for host address mappings is maintained by the IP layer. It contains information supplied by requests to the ARP layer. By default, an entry will expire 20 minutes after it was added to the table.

Another feature of the protocol is called gratuitous ARP. This occurs when a host broadcasts an ARP request for its own hardware address. A Solaris OE system does this at boot time. It is used to detect if another system is using its IP address, indicating a misconfigured system. The other use of gratuitous ARP is to send updated hardware address information. Systems that receive gratuitous ARP information will automatically update the hardware address information.

ARP Attacks

Several ARP problems can affect a system's expected operation. The TCP/IP network protocol suite requires correct hardware address information to ensure proper delivery of data. An Ethernet frame with an incorrect hardware address will not be processed by the intended system. All hardware address information is collected by the ARP layer. It gathers this information as it is needed and accepts information sent to it. The protocol is also stateless. The problems lie in the fact that the protocol allows any host to provide its own address information (correct or not). One system can provide information on the behalf of another system. Address information received by the ARP layer is processed whether it was directly requested or not. Additionally and more importantly, all address information received by a system is believed to be accurate.

There are two basic types of attacks possible with ARP: denial of service and spoofing. These attacks can prevent normal operations and can be used to compromise other systems on the local network. A denial of service attack can prevent one system from exchanging packets with another. This makes the system appear to be off the network. During a spoofing attack, one system masquerades as another.

These attacks take advantage of the dynamic nature of the protocol. The simplest attack is denial of service. There are two forms to this attack: local and remote. On the local system, an attacker who has administrative control of the system can insert bogus address information into the ARP cache. Packets destined for systems with bogus hardware addresses will not be received by the intended system. An attacker can feed a remote system incorrect address information as well. This is known as cache poisoning. Since the ARP layer always trusts the information it receives, wrong information can be inserted and current ARP entries can be corrupted. An attacker might use the publish feature of the ARP layer to broadcast incorrect information about other systems. If two ARP replies are received, the last one will be used. It might be the correct one, or it may not. This situation can spread discord throughout systems on the local network and be difficult to diagnose.

ARP spoofing attacks are more serious because they are used to compromise remote systems on the local network. By masquerading as another system, it is possible for an attacker to exploit a trust relationship and gain entry to other systems. This attack involves sending false hardware address information to a target system that the system will use to update its ARP tables. Once the false information is implanted, the attacking system changes its IP address and attempts a connection to the target.

For example, host A trusts host B. An attacker on host C wants to log into host A. First, the attacker must disable host B to prevent it from responding to ARP requests. The attacker then configures host C's IP address on a logical network interface and sends an ARP reply to host A containing host B's IP address and host C's hardware address. As discussed previously, host A will update the address information from the ARP reply. Host C now acts as host B, and the attacker can now log into host A.

ARP Defenses

Defending against ARP attacks is difficult. Changing the protocol in significant ways would break compatibility with all TCP/IP based systems on a network. Attempting to eliminate the dynamic nature of the protocol makes network administration a nightmare. However, there are some things that can be done to improve security on the network.

If false entries are inserted into the ARP and IP routing tables, there are two ways they can be deleted:

  • Entries can be deleted manually using the arp -d host_entry command.

  • Entries will timeout and be deleted by the system.

RFC 826, which defines ARP, specifies that ARP cache entries should be deleted automatically after a reasonable period of time. The default timeout values for unsolicited ARP cache entries are five minutes for all releases of the Solaris OE. IP routing table entries timeout after 20 minutes.

In Solaris OE versions 8 and newer, the following timeout intervals can be altered.

# ndd -set /dev/arp arp_cleanup_interval 60000
# ndd -set /dev/ip ip_ire_arp_interval

In Solaris OE versions 2.5.1 through 7, the ip_ire_arp_interval parameter is named ip_ire_flush_interval.

The timeout interval is specified in milliseconds. One minute equals 60000 milliseconds. Both these commands reduce the timeout period for the ARP cache and IP routing table. Entries will be deleted at a faster rate. This might slow down an ARP attack since bogus entries do not remain as long. These commands are available in the system init script provided in "Sample System nddconfig init Script" on page 26." The major side effect of this change is a greater number of ARP requests and replies will be sent. It might not be prudent to use on congested networks.

Another alternative is to manually create hardware address entries in the ARP cache. This solution can protect against some ARP attacks but breaks the dynamic nature of ARP, can increase maintenance costs, and may not be effective in most environments. A static entry in the ARP cache is a mapping of an IP address to hardware address. These entries can be loaded at system boot time. Create a file containing IP addresses and the corresponding hardware addresses, similar to the following:

gort.eng.sun.com 08:00:20:ba:a3:c5
olympics.eng.sun.com 08:00:20:4d:6d:30
switchblade.eng.sun.com 08:00:20:b3:48:57

Load the contents of this using the arp -f <file> command where file contains a table of hostnames and hardware addresses. These entries are now marked as permanent entries in the cache and will not be deleted by timeout. They can, however, be overridden by unsolicited information. In addition, they can still be deleted by using the arp -d <host_entry> command where host_entry is the host name to delete. This solution might not be appropriate in environments that frequently change equipment.

NOTE

Permanent ARP entries are only permanent in that they will not be timed-out. They can be overwritten by ARP information received over the network.

It is also possible to disable ARP completely for an interface. This means that the network interface will no longer send ARP requests nor process ARP replies. To disable ARP processing, use the ifconfig <interface> -arp command. Every system that disables ARP must have static ARP entries. Also, any system that might need to communicate with systems without ARP will need static ARP entries (such as routers). This solution is not recommended for most environments because of the high administrative costs. It might be effective with a small number of machines that need to communicate with each other and do not interact with other systems on the local network.

  • + Share This
  • 🔖 Save To Your Account

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