Manual Chapter : 3-DNS Administrator Guide version 4.2: Planning the 3-DNS Configuration

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3-DNS Controller versions 1.x - 4.x

  • 4.2 PTF-10, 4.2 PTF-09, 4.2 PTF-08, 4.2 PTF-07, 4.2 PTF-06, 4.2 PTF-05, 4.2 PTF-04, 4.2 PTF-03, 4.2 PTF-02, 4.2 PTF-01, 4.2.0
Manual Chapter


Planning the 3-DNS Configuration

Managing traffic on a global network

The 3-DNS is a sophisticated wide-area traffic manager. With 3-DNS, you can load balance web site traffic and distributed applications. You can also monitor the health of your network. This section provides a brief overview of how the 3-DNS works within a global network, and how it interacts with any BIG-IP, EDGE-FX Cache, GLOBAL-SITE, or host in the network. The section also illustrates how the 3-DNS works with the big3d agents that run in various locations in the network, and with the local DNS servers that make DNS requests on behalf of clients connecting to the Internet.

The following sample configuration shows the 3-DNS systems that load balance connections for a sample Internet domain,

Understanding a basic 3-DNS configuration

The 3-DNS systems in your network sit in specific data centers, and work in conjunction with the BIG-IP, EDGE-FX Cache, GLOBAL-SITE, and host servers that also sit in your network data centers. All 3-DNS systems in the network can receive and respond to DNS resolution requests from the LDNS servers that clients use to connect to the domain.

Figure 2.1 illustrates the layout of the 3-DNS, BIG-IP, and host servers in the three data centers. The Los Angeles data center houses one 3-DNS and one BIG-IP, as does the New York data center. The Tokyo data center houses only one 3-DNS and one host server.

In the Los Angeles and New York data centers, the big3d agent runs on the 3-DNS systems and the BIG-IP systems, but in the Tokyo data center, the big3d agent runs only on the 3-DNS. Each big3d agent collects information about the network path between the data center where it is running and the client's LDNS server in Chicago, as illustrated by the red lines. Each big3d agent also broadcasts the network path information it collects to the 3-DNS systems running in each data center, as illustrated by the green, blue, and purple lines.

Note: Each 3-DNS, BIG-IP, EDGE-FX Cache, and GLOBAL-SITE in a data center typically runs a big3d agent.

Figure 2.1 A sample network layout showing data paths

Synchronizing configurations and broadcasting performance metrics

3-DNS systems typically work in sync groups, where a group of systems shares load balancing configuration settings. In a sync group, any system that has new configuration changes can broadcast the changes to any other system in the sync group, allowing for easy administrative maintenance. To distribute metrics data among the systems in a sync group, the principal 3-DNS sends requests to the big3d agents in the network, asking them to collect specific performance and path data. Once the big3d agents collect the data, they each broadcast the collected data to all systems in the network, again allowing for simple and reliable metrics distribution.

Using a 3-DNS as a standard DNS server

When a client requests a DNS resolution for a domain name, an LDNS sends the request to one of the 3-DNS systems that is authoritative for the zone. The 3-DNS first chooses the best available virtual server out of a pool to respond to the request, and then returns a DNS resource record to the requesting local DNS server. The LDNS server uses the answer for the period of time defined within the resource record. Once the answer expires, however, the LDNS server must request name resolution all over again to get a fresh answer.

Figure 2.2 DNS name resolution process

Figure 2.2 illustrates the specific steps in the name resolution process.

  1. The client connects to an Internet Service Provider (ISP) and queries the local DNS server to resolve the domain name
  2. If the information is not already in the LDNS server's cache, the local DNS server queries a root server (such as InterNIC's root servers). The root server returns the IP address of the DNS systems associated with, which in this case runs on the 3-DNS.
  3. The LDNS then connects to one of the 3-DNS systems to resolve the name. The 3-DNS uses a load balancing mode to choose an appropriate virtual server to receive the connection, and then returns the virtual server's IP address to the LDNS.
  4. The LDNS caches the answer from the 3-DNS, and passes the IP address to the client.
  5. The client connects to the IP address through an ISP.

Load balancing connections across the network

Each of the 3-DNS load balancing modes can provide efficient load balancing for any network configuration. The 3-DNS bases load balancing on pools of virtual servers. When a client requests a DNS resolution, the 3-DNS uses the specified load balancing mode to choose a virtual server from a pool of virtual servers. The resulting answer to this resolution request is returned as a standard A record.

Although some load balancing configurations can get complex, most load balancing configurations are relatively simple, whether you use a static load balancing mode or a dynamic load balancing mode. More advanced configurations can incorporate multiple pools, as well as advanced traffic control features, such as topology or production rules.

For more information on specific load balancing modes, see Chapter 8, Load Balancing in the 3-DNS Reference Guide. For more information on load balancing configurations, review the sample configurations in Chapter 7, Configuring a Globally-Distributed Network , and Chapter 8, Configuring a Content Delivery Network . If you are unfamiliar with the 3-DNS, you may also want to review Chapter 6, Essential Configuration Tasks .

Working with 3-DNS systems and other products

The 3-DNS balances connections across a group of virtual servers that run in different data centers throughout the network. You can manage virtual servers from the following types of products:

  • BIG-IP
    A BIG-IP virtual server maps to a series of content servers.
  • EDGE-FX Cache
    An EDGE-FX Cache virtual server maps to cached content that gets refreshed at frequent intervals.
  • Generic host
    A host virtual server can be an IP address or an IP alias that hosts the content.
  • Other load balancing hosts
    Other load balancing hosts map virtual servers to a series of content hosts.

    Figure 2.3 illustrates the hierarchy of how the 3-DNS manages virtual servers.

    Figure 2.3 Load balancing management on a 3-DNS

Planning issues for the network setup

After you finish running the Setup utility, and connect each system to the network, you can set up the network and load balancing configuration on one 3-DNS, and let the sync group feature automatically broadcast the configuration to the other 3-DNS systems in the network. You do not have to configure the 3-DNS systems individually, unless you are planning an advanced configuration that requires different configurations for different data centers, or you are configuring the 3-DNS systems from the command line.

Tip: If you are configuring additional 3-DNS systems in a network that already has a 3-DNS in it, please review Chapter 11, Adding a 3-DNS to an Existing Network .

During the network setup phase, you define four basic aspects of the network layout, in the following order:

  • Base network
    The base network includes the interfaces, VLANs, and trunks for the network topology. Configuring the base network installs the 3-DNS in your physical network.
  • Data centers
    Data centers are the physical locations that house the equipment you use for load balancing.
  • Data center servers
    The data center servers that you define in the network setup include the 3-DNS, BIG-IP, EDGE-FX Cache, GLOBAL-SITE, and host systems that you use for load balancing and probing.
  • Sync group
    A sync group defines the group of 3-DNS systems that share configuration settings.

    Note: During the setup phase of configuration, we recommend that you connect to the 3-DNS from a remote workstation from which you can complete the remaining configuration tasks using the web-based Configuration utility.

Configuring the base network

The 3-DNS interfaces and the related topics of self IP addresses, VLANs, and trunks are collectively referred to, in this manual, as the base network. The base network, or at least an initial version of it, is configured when you run the Setup utility for the first time. The initial base network configuration also includes such things as the default route for the 3-DNS, fully qualified domain names, and certificate information that can only be configured using the Setup utility or its components. (To make changes to other base network components, such as domain names, default routes, and certificate information, refer to Chapter 4, Working with the Setup Utility , which describes the Setup utility and its various components.)

A 3-DNS usually has two network interfaces. Each active interface must be configured with a VLAN membership, and each VLAN must have a self IP address. Note that most 3-DNS configurations require only one interface, VLAN, and self IP address. However, if you are configuring the 3-DNS in bridge mode or router mode, you may need to configure two (or more) interfaces, depending on your network requirements. For more information on configuring the base network, refer to Chapter 5, Configuring the Base Network .

Defining data centers and servers

In the 3-DNS configuration, it is important that you define all of your data centers before you begin defining the data center servers because when you define a server, you specify the data center where the server runs. (You do this by choosing a data center from the list of data centers you have already defined.) To define a data center, you need only specify the data center name. To define a server, however, you need to specify the following items:

  • Server type (3-DNS, BIG-IP, EDGE-FX Cache, GLOBAL-SITE, or host)
  • Server IP address (or shared IP alias for redundant systems)
  • Name of the data center where the server runs
  • The big3d agent factories (on 3-DNS, BIG-IP, EDGE-FX Cache, and GLOBAL-SITE only)
  • Virtual servers managed by the server (BIG-IP, EDGE-FX Cache, and host servers only)
  • SNMP host probing settings (hosts only)

Note: One important aspect of planning your network setup is to decide how to set up the big3d agent, and which ports you need to open for communications between the systems in your network. See the 3-DNS Reference Guide, Chapter 4, The big3d Agent, for help with determining how both of these issues affect your installation.

Planning a sync group

A sync group is a group of 3-DNS systems that share configuration information. In a sync group, a principal 3-DNS issues requests to the big3d agents on all the other systems to gather metrics data. Both the principal 3-DNS and the receiver 3-DNS systems in the group receive broadcasts of metrics data from the big3d agents. All members of the sync group also receive broadcasts of updated configuration settings from the 3-DNS that has the latest configuration changes.

When you define the sync group, you select the sync group members from the list of 3-DNS systems you have already defined. The sync group lists the 3-DNS systems in the order in which you selected them. The first 3-DNS in the list becomes the principal 3-DNS. The remaining 3-DNS systems in the list become receivers. If the principal 3-DNS becomes disabled, the next 3-DNS in the list becomes the principal 3-DNS until the original principal 3-DNS comes back online.

Understanding how a sync group works

The sync group feature synchronizes individual configuration files, such as wideip.conf, and other files that store system settings. You have the option of adding files to the synchronization list.

The 3-DNS systems in a sync group operate as peer servers. At set intervals, the syncd utility compares the time stamps of the configuration files earmarked for synchronization on all of the 3-DNS systems. If the time stamp on a specific file differs between 3-DNS systems, the 3-DNS with the latest file broadcasts the file to all of the other 3-DNS systems in the group.

Understanding how the time tolerance variable affects a sync group

The time tolerance variable is a global variable that defines the number of seconds that the time setting on one 3-DNS can be ahead or behind the time setting on another 3-DNS. If the difference between the times on the systems is greater than the time tolerance, the time setting on the 3-DNS running behind is reset to match the 3-DNS with the most recent time. For example, if the time tolerance is 5 seconds, and one 3-DNS is running 10 seconds ahead of the other, the 3-DNS running behind has its time reset to match the one running 10 seconds ahead. If the second system was running only 2 seconds ahead of the other, the time settings would remain unchanged. The values are 0, 5, and higher (values of 1-4 are automatically set to 5, and 0 turns off time synchronization). The default setting is 10 seconds.

The time setting on 3-DNS systems is important because a 3-DNS compares time stamps on files when deciding whether to synchronize files with other 3-DNS systems in the sync group.

Setting up communications on a 3-DNS

There are three different communication issues that you need to resolve when you set up communication between the 3-DNS systems running in your network

  • 3-DNS systems communicating with other 3-DNS systems
    To allow 3-DNS systems to communicate with each other, you must set up ssh and scp utilities for crypto systems (that use SSH and SCP) that communicate with other crypto systems, and you must set up rsh and rcp utilities for systems that communicate with non-crypto systems (that do not use SSH and SCP).
  • 3-DNS communicating with BIG-IP, EDGE-FX Cache, and GLOBAL-SITE
    To allow 3-DNS to communicate with BIG-IP, EDGE-FX Cache, and GLOBAL-SITE, you address the same ssh and rsh issues. Crypto systems communicating with other crypto systems can use ssh and scp utilities, but systems communicating with non-crypto systems require rsh and rcp utilities.
  • 3-DNS communicating with big3d agents
    To allow communications between big3d agents and the 3-DNS, you need to configure iQuery ports on any 3-DNS, BIG-IP, EDGE-FX Cache, and GLOBAL-SITE systems that run the big3d agent.

Note: Enabling RSH and RCP does not prevent crypto 3-DNS systems from using encryption when they communicate with other crypto 3-DNS, BIG-IP, EDGE-FX Cache, or GLOBAL-SITE systems.

Setting up communication between crypto and non-crypto systems

The 3-DNS systems in your network need to communicate with each other in order to synchronize configuration and performance data. If you use exclusively crypto 3-DNS systems (those that use the SSH protocol), or exclusively non-crypto 3-DNS systems (those that use the RSH protocol), the communication tools set up by the Setup utility are all you need.

If your network is a mixed environment, that is, composed of both crypto and non-crypto systems, you need to enable the rsh and rcp utilities on the crypto systems. Though the rsh and rcp utilities come pre-installed on the crypto systems, you must explicitly enable these utilities. You can enable the utilities when you run the Setup utility, or you can run the config_rshd script from the command line. Table 2.1 shows the ports and protocols used by 3-DNS for crypto and non-crypto communications.

Communications between 3-DNS systems




From Port



Crypto 3-DNS

Crypto 3-DNS





Crypto 3-DNS

Non-crypto 3-DNS





Non-crypto 3-DNS

Crypto 3-DNS





Non-crypto 3-DNS

Non-crypto 3-DNS





Setting up data collection with the big3d agent

The big3d agent collects performance information from other 3-DNS, BIG-IP, GLOBAL-SITE, and EDGE-FX Cache systems on behalf of the 3-DNS you are configuring. 3-DNS then uses this performance data for load balancing. The big3d agent uses factories to manage the data collection. For detailed information on configuring the big3d agent, managing the factories, opening the UDP ports, and working with firewalls, review Chapter 3, The big3d Agent, in the 3-DNS Reference Guide.

Choosing the 3-DNS mode

The 3-DNS can run in one of three modes: node, bridge, router. The base network configuration changes depending on which mode you choose. The following sections describe the three modes and provide basic configuration examples.

Running a 3-DNS in node mode

Node mode is the traditional way to configure the 3-DNS. The benefits of running the 3-DNS in node mode are as follows:

  • You can replace your name servers with 3-DNS systems.
  • You can use the 3-DNS as the authoritative DNS server for your domain.
  • You can manage your DNS zone files with NameSurfer.

    When you replace your DNS servers with 3-DNS, you can use the extensive wide-area traffic management capabilities of the 3-DNS in conjunction with the standard DNS protocol. When the 3-DNS receives a request that matches a wide IP, it routes that request to the best virtual server in your network. When 3-DNS receives a non-matching request, that request is handled by the BIND utility (named) that is running on the 3-DNS.

    When you configure the 3-DNS to be authoritative for your domain, you can easily manage DNS zone files using NameSurfer, a browser-based, third-party application included on the 3-DNS. When you define wide IPs in the Configuration utility, the NameSurfer application automatically makes the appropriate additions to the zone files. The changes are then broadcast to the other 3-DNS systems in your network.

Note: If you configure wide IPs from the command line, you need to make the corresponding zone file changes from the command line.

Using the 3-DNS synchronization features

If you use the advanced synchronization features of the 3-DNS, we strongly recommend that you configure each 3-DNS to run as authoritative for the domain. This type of configuration offers the following advantages:

  • You can change zone files on any one of the 3-DNS systems in the network and have those changes automatically broadcast to all of the other systems in the network.
  • Each 3-DNS has the most up-to-date zone files, providing you one or more layers of redundancy.
  • The NameSurfer application automatically controls the addition, configuration, and deletion of zone files.

Importing BIND files to NameSurfer during an initial installation

During the initial configuration, you can specify that the 3-DNS import any existing BIND files from your name server to the 3-DNS. During the initial configuration, you can also designate NameSurfer as the primary name server for your domain. This forces NameSurfer to automatically format your BIND files in the NameSurfer format. For more information, refer to the NameSurfer documentation available from the home screen in the Configuration utility.

Running a 3-DNS in bridge mode or router mode

Running the 3-DNS in bridge mode or router mode offers the following benefits:

  • You gain the wide-area traffic management capabilities of the 3-DNS without disrupting your current DNS system.
  • In an enterprise, you can install, configure, and test the 3-DNS before you add the system to your production environment.
  • You do not use NameSurfer to manage your zone files.
  • You can load balance requests across two separate IP networks.

    When you configure the 3-DNS in bridge mode, you install the 3-DNS into your network so that all DNS requests are intercepted by the 3-DNS before they are sent to your name server for resolution. Based on the content of the request, the 3-DNS does one of the following:

  • If the request matches a wide IP managed by the 3-DNS, the system responds to the request with the best available virtual server in your network.
  • If the request does note match any wide IPs managed by the 3-DNS, the system forwards the request to the DNS server for resolution.

Planning issues for the load balancing configuration

The final phase of installing a 3-DNS is setting up the load balancing configuration. Load balancing configurations are based on pools of virtual servers in a wide IP. When the 3-DNS receives a connection request, it uses a load balancing mode to determine which virtual server in a given pool should receive the connection. The virtual servers in the pool can be the virtual servers managed by a BIG-IP, virtual servers managed by an EDGE-FX Cache, virtual servers managed by a generic host server, or they can be individual host servers themselves. Note that the 3-DNS continuously verifies which virtual servers in the pool are currently available to accept load balanced connections.

Simple configurations typically use a single pool of virtual servers and a load balancing mode that does not require significant additional configuration steps, such as Round Robin or Hops. More advanced load balancing configurations can use multiple wide IPs, multiple pools, customized load balancing modes, and other advanced traffic control features, such as topology load balancing and production rules.

We have included two popular 3-DNS configurations in this Administrator Guide, in Chapter 7, Configuring a Globally-Distributed Network , and in Chapter 8, Configuring a Content Delivery Network .

Using advanced traffic control features

The 3-DNS offers two advanced features that you can configure to further control the distribution and flow of network traffic.

  • Topology load balancing
    With Topology load balancing, you can direct client requests to virtual servers in the geographically closest data center. You can set up Topology load balancing between pools, or within a pool. For details about working with topology-based features, see Chapter 7, Configuring a Globally-Distributed Network , and in the 3-DNS Reference Guide, see Chapter 13, Topology.
  • Production rules
    Production rules are a policy-based management feature that you can use to dynamically change the load balancing configuration and the system settings based on specific triggers, such as the time of day, or the current network traffic flow. You can set up standard production rules using the Configuration utility, or you can define custom production rules using the production rules scripting language. Refer to Chapter 10, Production Rules, in the 3-DNS Reference Guide, for information about setting up production rules.