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Manual Chapter: big3d Agent
Manual Chapter
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The big3d agent runs on all BIG-IP® systems, collects performance information on behalf of the Global Traffic Manager system, and continually monitors the availability of the servers that Global Traffic Manager load balances. The utility also monitors the integrity of the network paths between the servers that host the domain, and the various local DNS servers that attempt to connect to the domain. Each big3d agent broadcasts its collected data to all of the Global Traffic Manager systems and Link Controller systems in your network, ensuring that these systems work with the latest information.
You can turn off the big3d agent on any BIG-IP system at any time; however, if you turn off the big3d agent on a server, Global Traffic Manager can no longer check the availability of the server or its virtual servers, and the statistics screens display the status of these servers as unknown (blue ball).
Tip: F5 Networks recommends that you have at least one BIG-IP system running the big3d agent in each data center in your network. This ensures that Global Traffic Manager has timely access to the metrics associated with network traffic.
A big3d agent collects the following types of performance information that the system uses for load balancing. The big3d agent broadcasts this information to all Global Traffic Manager systems in your network.
Network path round trip time
The big3d agent calculates the round trip time for the network path between the utilitys data center and the clients LDNS that is making the resolution request. 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 utilitys data center and the clients LDNS that is making the resolution request. 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 utilitys data center and the clients LDNS. 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. 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. 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 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.
Setting up communications between big3d agents and other systems
Before the big3d agents can communicate with the Global Traffic Manager systems 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 Manager systems in the network.
The big3d agent is installed by running the big3d_install script. With the correct ports open, Global Traffic Manager also automatically updates older big3d agents on the network.
When you install the big3d agent, you must complete the following tasks:
Open ports 22 and 4353 between the Global Traffic Manager system and the other BIG-IP systems.
The big3d agents collect and broadcast information on demand. 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 Manager systems running in the network.
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). 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 local DNS servers that make name resolution requests. The more local DNS 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.
In order to copy big3d agents from a Global Traffic Manager system to BIG-IP systems, the Global Traffic Manager system must be able to communicate with these other systems. Specifically, every BIG-IP system, which you define as a server on the Global Traffic Manager system, must have sufficient network privileges and configured routes to be able to probe the virtual servers that it hosts, as well as the virtual servers hosted by other servers defined on the Global Traffic Manager systems in a synchronization group.
In the following configuration, every big3d agent that the Global Traffic Manager synchronization group recognizes must be able to probe the virtual server 10.1.0.1:80 via TCP.
The iQuery® protocol uses one of two ports to communicate between the big3d agents throughout the network and Global Traffic Manager systems. The ports used by iQuery traffic change, depending on whether the traffic is inbound from the big3d agent or outbound from Global Traffic Manager.
Table A.1 shows the protocols and ports for both inbound and outbound iQuery communications between Global Traffic Manager systems and big3d agents distributed in your network.
Table A.1 Communication between big3d agents and Global Traffic Manager systems
big3d agent
big3d agent
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 between big3d agents and SNMP agents on hosts
big3d agent
Ephemeral ports used to make SNMP queries for host statistics
big3d agent
Ephemeral ports used to receive host statistics using SNMP
Table A.3 shows the ports used for communications between big3d agents and virtual servers that are not hosted by a BIG-IP system.
Table A.3 Communication between big3d agents and virtual servers not hosted by BIG-IP systems
big3d agent
big3d agent
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 system. 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. 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 system. 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.
Table A.4 shows the protocols and ports that the big3d agent uses when collecting path data for local DNS servers.
Table A.4 Communications between big3d agents and local DNS servers
Probe using TCP (Cisco® routers: allow establish)
Replies using TCP (Cisco® routers: allow establish)
Probe using UDP or traceroute utility
dns_rev
dns_dot
dns_rev
dns_dot
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