IP SLA Responder and IP SLA Control Protocol
The IP SLA responder is a component embedded in the destination Cisco device that allows the system to
anticipate and respond to IP SLA request packets. The responder provides accurate measurements without
the need for dedicated probes. The responder uses the Cisco IOS IP SLA Control Protocol to provide a
mechanism through which it can be notified on which port it should listen and respond.
The IP SLA responder can be a Cisco IOS Layer 2, responder-configurable switch. The responder does
not need to support full IP SLA functionality.
Note
The following figure shows where the Cisco IOS IP SLA responder fits in the IP network. The responder
listens on a specific port for control protocol messages sent by an IP SLA operation. Upon receipt of the
control message, it enables the specified UDP or TCP port for the specified duration. During this time, the
responder accepts the requests and responds to them. It disables the port after it responds to the IP SLA packet,
or when the specified time expires. MD5 authentication for control messages is available for added security.
Figure 114: Cisco IOS IP SLAs Operation
You do not need to enable the responder on the destination device for all IP SLA operations. For example, a
responder is not required for services that are already provided by the destination router (such as Telnet or
HTTP).
Related Topics
Configuring the IP SLA Responder, on page 2030
Restrictions on SLAs, on page 2025
Monitoring IP SLA Operations, on page 2031
Response Time Computation for IP SLAs
Switches, controllers, and routers can take tens of milliseconds to process incoming packets due to other high
priority processes. This delay affects the response times because the test-packet reply might be in a queue
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
2028
Information About SLAs
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