Cisco 350 Series Administration Manual page 454

IP Configuration: SLA
Overview
Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
IP SLAs object tracking relies on IP SLAs operations to detect connectivity to a certain
network destination. IP SLA operation sends ICMP packets to the address defined by user (the
required next hop), and monitors success or failure of replies from the host. A track object is
used to track operation results and set the status to up or down based on the success or failure
of the ICMP destination.
A track object status can be used by various applications in decisions that require knowledge
of network connectivity. One example of such an application is VRRP. The track object is
assigned to a VRRP router. If track status is down, the VRRP priority of router is decremented
by a value defined by user. If track status is up, the original VRRP priority of the router is
maintained.
IP SLA Tracking for IPv4 Static Routes
When using static routing, a situation may exist where a static route is active, but the
destination network is not reachable via the specified next hop. For example, if the static route
in question has the lowest metric to the destination network and the outgoing interface to the
next hop is Up, however the connectivity is "broken" somewhere along the path to the
destination network. In this case, the device may use the static route although it does not
actually provide connectivity to the destination network. The IP SLA Object tracking for static
routes provides a mechanism to track the connectivity to the destination network via the next
hop specified in the static route If connectivity to the destination network is lost, the route state
is set to Down, and, if available, a different static route (which is in state Up) can now be
selected for routing traffic.
Similar to IP SLAs tracking for VRRP, IP SLAs object tracking for static routes also relies on
IP SLAs operations to detect connectivity to destination networks. IP SLAs operation sends
ICMP packets to the address defined by the user (a host on the required destination network),
and also defines the next hop to use for the ping operation. IP SLAs operation then monitors
success or failure of replies from the host. A track object is used to track operation results and
set the status to Up or Down, based on the success or failure of the ICMP destination. The
track operation is assigned to a static route. If the track status is down, the static route state is
set to Down. If track status is Up, the static route state remains Up.
The following describes the main terms used in this section:
• Operation—Each IP SLAs ICMP Echo operation sends a single ICMP Echo request
to a target address at a configured frequency rate. It then waits for a response.
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