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Manual Chapter: Configuration Guide for BIG-IP® Global Traffic Management: A - Working with the big3d Agent
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A

Working with the big3d Agent


Introducing the big3d agent

The big3d agent collects performance information on behalf of the Global Traffic Manager. The big3d agent runs on all BIG-IP systems. In most cases, you want to run a big3d agent on all of these systems in the network, but you can turn off the big3d agent on any system at any time. If you turn off the big3d agent on a server, the Global Traffic Manager can no longer check the availability of the server or its virtual servers, and the statistics screens display the status as unknown (blue ball). The big3d agent is a critical component of the Global Traffic Manager; without it, the Global Traffic Manager cannot access much of the information you need regarding other BIG-IP systems on the network.

Note

We recommend that you have a big3d agent running on at least one system in each data center in your network. This configuration ensures that the Global Traffic Manager has timely access to the metrics associated with network traffic

Collecting path data and server performance metrics

A big3d agent collects the following types of performance information used for load balancing. The big3d agent broadcasts this information to all Global Traffic Managers in your network.

  • Network path round trip time
    The big3d agent calculates the round trip time for the network path between the agent's data center and the client's LDNS server that is making the resolution request. The Global Traffic Manager uses round trip time to determine the best virtual server to answer the request when a pool uses a dynamic load balancing mode, such as Round Trip Time, or Quality of Service.
  • Network path packet loss
    The big3d agent calculates the packet completion percentage for the network path between the agent's data center and the client's LDNS server that is making the resolution request. The Global Traffic Manager uses the packet completion rate to determine the best virtual server to answer the request when a wide IP or pool uses either the Completion Rate or the Quality of Service load balancing modes.
  • Router hops along the network path
    The big3d agent calculates the number of intermediate system transitions (router hops) between the agent's data center and the client's LDNS server. The Global Traffic Manager uses hops to determine the best virtual server to answer the request when a pool uses the Hops or the Quality of Service load balancing modes.
  • Server performance
    The big3d agent returns server metrics, such as the packet rate, for BIG-IP systems or SNMP-enabled hosts. The Global Traffic Manager uses packet rate to determine the best virtual server to answer the request when a pool uses the Packet Rate, KBPS, Least Connections, or Quality of Service load balancing modes.
  • Virtual server availability and performance
    The big3d agent queries virtual servers to verify whether they are up and available to receive connections, and uses only those virtual servers that are up for load balancing. The big3d agent also determines the number of current connections to virtual servers that are defined on BIG-IP systems or SNMP-enabled hosts. The Global Traffic Manager uses the number of current connections to determine the best virtual server when a pool uses the Least Connections or VS Capacity load balancing mode.

Setting up data collection with the big3d agent

Setting up the big3d agents involves the following tasks:

  • Installing big3d agents on BIG-IP systems
    Each new version of the Global Traffic Manager software includes the latest version of the big3d agent. You need to distribute that copy of the big3d agent to each BIG-IP system in the network. See the release notes provided with the Global Traffic Manager software for information about which versions of the BIG-IP software the current big3d agent supports. For details on installing the big3d agent, see Installing the big3d agent , following.
  • Setting up communications between big3d agents and other systems
    Before the big3d agents can communicate with the Global Traffic Managers in the network, you need to configure the appropriate ports and tools to allow communication between the devices running the big3d agent and Global Traffic Managers in the network. These planning issues are discussed in Setting up communication between Global Traffic Managers and other servers .

Installing the big3d agent

The big3d agent is installed by running the big3d_install script. With the correct ports open, the Global Traffic Manager also automatically updates older big3d agents on the network.

When you install the big3d agent, you must complete the following tasks:

  • Install the Global Traffic Manager.
  • Add the BIG-IP systems as servers to the Global Traffic Manager.
  • Exchange the appropriate Web certificates between the Global Traffic Manager and other systems.
  • Open ports 22 and 4353 between the Global Traffic Manager and the other BIG-IP systems.

The big3d agent installed with the Global Traffic Manager automatically attempts to communicate with the other BIG-IP systems. If it determines that it is communicating with an older big3d agent, it automatically replaces that agent with the latest version.

Understanding the data collection and broadcasting sequence

The big3d agents collect and broadcast information on demand. The Global Traffic Manager in a synchronization group issues a data collection request to all big3d agents running in the network. In turn, the big3d agents collect the requested data, and then broadcast that data to all Global Traffic Managers running in the network.

Evaluating big3d agent configuration trade-offs

You must run a big3d agent on each BIG-IP system in your network if you use dynamic load balancing modes (those that rely on path data). (For information about dynamic load balancing, see Chapter 7, Load Balancing with the Global Traffic Manager .) You must have a big3d agent running on at least one system in each data center to gather the necessary path metrics.

The load on the big3d agents depends on the timer settings that you assign to the different types of data the big3d agents collect. The shorter the timers, the more frequently the big3d agent needs to refresh the data. While short timers guarantee that you always have valid data readily available for load balancing, they also increase the frequency of data collection.

Another factor that can affect data collection is the number of client LDNS servers that make name resolution requests. The more LDNS servers that make resolution requests, the more path data that the big3d agents have to collect. While round trip time for a given path may vary constantly due to current network load, the number of hops along a network path between a data center and a specific LDNS does not often change. Consequently, you may want to set short timer settings for round trip time data so that it refreshes more often, but set high timer settings for hops data because it does not need to be refreshed often.

Setting up communication between Global Traffic Managers and other servers

In order to copy big3d agents from a Global Traffic Manager to BIG-IP systems, the Global Traffic Manager must be able to communicate with the other systems.

Setting up iQuery communications for the big3d agent

The iQuery protocol uses one of two ports to communicate between the big3d agents throughout the network and Global Traffic Managers. The ports used by iQuery traffic change, depending on whether the traffic is inbound from the big3d agent or outbound from the Global Traffic Manager.

Table A.1 shows the protocols and ports for both inbound and outbound iQuery communications between Global Traffic Managers and big3d agents distributed in your network.

Table A.1 Communication protocols and ports between Global Traffic Managers and big3d agents
From
To
Protocol
From Port
To Port
GTM system
big3d agent
TCP

4354

4353

GTM system
big3d agent
TCP

>1023

4353

 

Table A.2 shows the protocols and corresponding ports used for iQuery communications between big3d agents and SNMP agents that run on host servers.

Table A.2 Communication protocols and ports between big3d agents and SNMP agents on hosts
From
To
Protocol
From Port
To Port
Purpose
big3d agent
host SNMP agent
UDP

>1023

161

Ephemeral ports used to make SNMP queries for host statistics
host SNMP agent
big3d agent
UDP

161

>1023

Ephemeral ports used to receive host statistics using SNMP

 

If you run a big3d agent on a Global Traffic Manager system or a BIG-IP system, and you set the SNMP monitor to 1 or higher, the big3d agent automatically opens the appropriate UDP ports to allow for SNMP communications. If you do not want to open the UDP ports for this purpose, you need to set the SNMP factory count to 0.

Allowing iQuery communications to pass through firewalls

The payload information of an iQuery packet contains information that potentially requires network address translation when there is a firewall in the path between the big3d agent and the Global Traffic Manager. The firewall translates only the packet headers, not the payloads.

The virtual server translation option resolves this issue. When you configure address translation for virtual servers, the iQuery packet stores the original IP address in the packet payload itself. When the packet passes through a firewall, the firewall translates the IP address in the packet header normally, but the IP address within the packet payload is preserved. The Global Traffic Manager reads the IP address out of the packet payload, rather than out of the packet header.

For example, firewall separates the path between a BIG-IP system running a big3d agent, and the Global Traffic Manager. The packet addresses are translated at the firewall. However, addresses within the iQuery payload are not translated, and they arrive at the BIG-IP system in their original states.

Communications between Global Traffic Managers, big3d agents, and local DNS servers

Table A.3 shows the protocols and ports that the big3d agent uses when collecting path data for local DNS servers.

Table A.3 Communications between big3d agents and local DNS servers
From
To
Protocol
From Port
To Port
Purpose
big3d
LDNS
ICMP

N/A

N/A

Probe using ICMP pings
big3d
LDNS
TCP

>1023

53

Probe using TCP (Cisco© routers: allow establish)
LDNS
big3d
TCP

53

>1023

Replies using TCP (Cisco© routers: allow establish)
big3d
LDNS
UDP

53

33434

Probe using UDP or traceroute utility
LDNS
big3d
ICMP

N/A

N/A

Replies to ICMP, UDP pings, or traceroute probes
big3d
LDNS
dns_rev
dns_dot

>1023

53

Probe using DNS rev or DNS dot
LDNS
big3d
dns_rev
dns_dot

53

>1023

Replies to DNS rev or DNS dot probes

 




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