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Manual Chapter: Understanding Core System Services
Manual Chapter
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A number of system services start up automatically when you boot the BIG-IP® system. Table C.1 lists the BIG-IP system services that start up at boot time, and indicates the impact to BIG-IP system operation if the service is not running:
Cannot send alerts to front panel; cannot send SNMP traps; cannot monitor and handle error messages.
Cannot process switch traffic; LEDs, Link Aggregation Control Protocol (LACP) and spanning tree protocols (STP) cannot function.
Provides initial bigdb database values to the MCPD service and persists any database changes to the BigDB.dat file.
Provides chassis monitoring and configuration, as well as other related functions.
Cannot perform platform identification, send platform information to MCPD service, or start SCCP services.
Creates trunks based on the industry-standard Link Aggregation Control Protocol (LACP) and controls the Switchboard Fail-safe feature for redundant systems.
Cannot manage traffic; cannot retrieve or update system status; users cannot reconfigure system; disables some of the other services.
Provides System Network Management Protocol (SNMP) functions. Also includes the two subagents rmondsnmpd and tmsnmpd.
Implements the IEEE spanning tree protocols for preventing bridging loops.
Cannot perform remote authentication/authorization.
In almost no case do you ever need to explicitly stop a core service from running. (The TMM service is a notable exception.) For this reason, you cannot use the Configuration utility to start or stop a core service. If you want to explicitly stop or start a core service, you use the bigstart command line utility. For information on the bigstart utility, see the bigstart man page. For information on stopping the TMM service, see Understanding the Traffic Management Microkernel service.
The core services MCPD, TMM, and SOD are important because they support key functions of the BIG-IP system. These services run automatically unless you specifically stop them. They provide essential functions such as maintaining the BIG-IP system configuration data, passing application traffic through TMM switch interfaces, and performing failover for redundant system configurations.
Note: You can define the action that you want the BIG-IP system to take when the system fails to detect a heartbeat for a core service. For more information, see Chapter 16, Configuring High Availability.
The Master Configuration Process service (MCPD) manages the configurations on a BIG-IP system. The primary purpose of the MCPD service is to:
Receive and process configuration change requests from MCP clients, validate configuration change requests based on database schema and other complex BIG-IP system business rules, and update storage for the target configuration. The service also returns success or failure results to clients.
Receive and process statistics and configuration query requests from MCP clients and return query results to the clients.
Support a publish-and-subscribe interface, where the service can notify all interested MCP clients of any configuration changes that might be of interest to those clients.
The Traffic Management Microkernel (TMM) service is the process running on the BIG-IP system that performs most traffic management for the product. As such, the TMM service supports all system and networking components that the BIG-IP system needs in order to process application and administrative traffic. The TMM service controls all system interfaces, except for the management interface (MGMT).
The TMM service affects the type of interface (TMM switch interface or management interface) that the BIG-IP system uses for network traffic. The effect on the use of BIG-IP interfaces differs depending on the type of traffic. Normally, when the TMM service is running, certain types of network traffic use the management interface, while other types of traffic use the TMM switch interfaces:
User application traffic
This type of traffic is typically application traffic either destined for or coming from a load balancing server or other network device. User application traffic always uses TMM switch interfaces, and never uses the management interface. Therefore, if the TMM service is stopped, the BIG-IP system does not process this type of traffic.
Administrative traffic destined for the BIG-IP system
This type of traffic is traffic destined for the IP address of the BIG-IP systems management interface. The BIG-IP system then sends its responses to these requests back through the management interface. (The exception to this is UDP traffic, which the BIG-IP system sends out using the TMM default route.) Because administrative traffic uses the management interface, the BIG-IP system can still process this type of traffic when the TMM service is not running.
Administrative traffic coming from the BIG-IP system
The BIG-IP system generates this type of administrative traffic, and the source for this type of traffic is the IP address of the management interface. When the TMM service is running, the BIG-IP system sends this type of traffic through a TMM switch interface, using the TMM default route. If the TMM service becomes unavailable, this type of traffic uses the management interface.
Warning: When the TMM service is running, ensure that you have defined a default route in the main TMM routing table. Defining a TMM default route prevents high volumes of administrative traffic generated by the BIG-IP system from using the management interface. For more information, see Chapter 10, Configuring Routes and Route Domains.
To summarize, Figure C.2 lists the three main traffic types, and shows the type of BIG-IP system interface that each traffic type uses when the TMM service is running.
Administrative traffic destined for management interface IP address
(for non-UDP traffic)
(for UDP traffic, when TMM default route is defined)
Administrative traffic that the BIG-IP system generates
(when TMM default route is defined)
Note: See note following this table.
Note: Traffic generated by the ntpd service in particular does not normally use a TMM interface when the TMM is running. Instead, the service uses the MGMT interface. The only case in which the ntpd service uses a TMM interface is when the ntpd service has been restarted for some reason. In this case, the service switches from using the MGMT interface to using a TMM interface. For more information on the ntpd service, see Chapter 2, Configuring the BIG-IP Platform and General Properties.
There are certain administrative tasks, however, such as a BIG-IP software installation, that you should never perform while the TMM service is running. Prior to performing these tasks, you should shut down the TMM service.
When you stop the TMM service and therefore make the TMM interfaces unavailable, the management interface becomes the only available interface on the BIG-IP system for administrative traffic. Figure C.3 shows the type of interface that each traffic type uses when the TMM is stopped.
Administrative traffic destined for management interface IP address
Administrative traffic that the BIG-IP system generates
Important: The BIG-IP system drops UDP packets when the TMM service is running but no TMM default route is defined.
Other administrative tasks that you should perform using the management interface only (because they require you to stop the TMM service) are a PXE installation and boot, and remote management using SSH and HTTPS.
Important: The BIG-IP system normally routes remote authentication traffic through a Traffic Management Microkernel (TMM) switch interface (that is, an interface associated with a VLAN and a self IP address), rather than through the management interface. Therefore, if the TMM service has been stopped for any reason, remote authentication is not available until the service is running again. For information on configuring remote authentication of application traffic, see the Configuration Guide for BIG-IP® Local Traffic Management.
The SOD service runs on a unit of a redundant system and monitors the peer unit. If the redundant system is an active/standby configuration, the SOD service runs on the standby unit and monitors the active unit. If the redundant system is an active-active configuration, the SOD service runs on both units, and each SOD service monitors the peer unit. When the SOD service determines that the peer unit is no longer responding, the service initiates failover.
The SOD service can monitor the active unit in two ways, either through a serial line (known as hard-wired failover) or through the network (known as network failover). The default configuration for the SOD service is to perform hard-wired failover.
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