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Archived Manual Chapter: BIG-IP Link Controller Reference Guide v4.3: The big3d Agent
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3

The big3d Agent



Working with the big3d agent

The big3d agent collects performance information on behalf of the Link Controller. Before the big3d agents can communicate with the Link Controllers in the network, you need to configure the appropriate ports and tools to allow communication between the devices running the big3d agent and Link Controllers in the network. These planning issues are discussed in Communications for remote administration of the Link Controller, on page 3-3 .

Collecting path data and server performance metrics

A big3d agent collects the following types of performance information used for load balancing.

  • Virtual server availability
    The big3d agent queries virtual servers to verify whether they are up and available to receive connections. For name resolution, the Link Controller uses only those virtual servers that are up.
  • Network path round trip time
    The big3d agent calculates the round trip time for the network path between the Link Controller and the client's LDNS server that is making the resolution request. The round trip time is used to determine the best virtual server to answer the request when you use the Round Trip Times or the Quality of Service load balancing modes.
  • Network path packet loss
    The big3d agent calculates the packet completion percentage for the network path between the data center and the client's LDNS server that is making the resolution request. Packet completion is used to determine the best virtual server to answer the request when you use 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 systems transitions (router hops) between the data center and the client's LDNS server. Hops are used to determine the best virtual server to answer the request when you use the Hops or the Quality of Service load balancing modes.
  • Server performance
    The big3d agent calculates server metrics, such as the packet rate for Link Controller virtual servers. Packet rate is used to determine the best virtual server to answer the request when you use the Packet Rate or the Quality of Service load balancing modes.
  • Virtual server performance
    The big3d agent calculates the number of connections to virtual servers defined on the Link Controller. The number of virtual server connections is used to determine the best virtual server when using the Least Connections load balancing mode.

Understanding factories run by big3d agents

To gather performance information, the big3d agent uses different types of factories. A factory is a process that collects different types of data. The big3d agent currently supports the following factory types:

  • Prober factory
    A prober factory collects several types of information using ICMP, TCP, UDP, DNS_DOT, or DNS_REV protocols. This factory queries local DNS servers. For local DNS servers, the prober factory uses the response time to calculate the round trip time and packet loss between the LDNS and the Link Controller.
  • Hops factory
    A hops factory uses the traceroute utility to calculate the number of intermediate systems transitions (or router hops) along the network path between the Link Controller and a client LDNS.
  • SNMP factory
    An SNMP factory queries the SNMP agents that run on routers to collect performance metrics for the router.

Note: You cannot configure the factories on a Link Controller.

Tracking LDNS probe states with the big3d agent

The Link Controller tracks the state of path data collection for each LDNS that has ever requested a name resolution from the system. Table 3.1 shows the states that can be assigned to an LDNS. Note that you can view the state of LDNS servers in the Local DNS Statistics screen in the Configuration utility.

Probe and discovery states for individual client LDNS servers

State

Description

Needs Probe

The big3d agent has never collected data for the LDNS, or the data has expired.

Idle

The big3d agent successfully collected data for the LDNS, and is waiting for the next collection request.

In Probe

The big3d agent is currently collecting data for the LDNS.

Overview of communications protocols

The Link Controller supports the following communications protocols.

Communications for remote administration of the Link Controller

The Configuration utility is a browser-based utility through which you can administer the Link Controller from a remote workstation. Table 3.2 shows the port that is used for remote administrative connections to the Link Controller web server, which hosts the Configuration utility.

Communications between Link Controllers and remote workstations

From

To

Protocol

Port

Purpose

Configuration utility on a remote workstation

Link Controller

https over TCP

443

Connection to secure web server

Communications for resolving DNS requests

Table 3.3 shows the ports on which the Link Controller receives and responds to DNS resolution requests issued by local DNS servers for inbound load balancing.

DNS communications on the Link Controller

From

To

Protocol

From Port

To Port

Purpose

LDNS

Link Controller

UDP

53 or >1024

53

DNS resolution requests

Link Controller

LDNS

UDP

53

53 or >1024

DNS resolution responses

Communications for collecting path data

Table 3.4 shows the protocols and ports that the big3d agent uses when collecting path data for local DNS servers. The Link Controller uses path data for dynamic load balancing modes.

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 version or DNS dot

LDNS

big3d

dns_rev
dns_dot

53

>1023

Replies to DNS version or DNS dot probes

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