IP SLA Questions
IP SLA PBR (Policy-Based Routing) Object Tracking allows you to make sure that the next hop is reachable before that route is used. If the next hop is not reachable, another route is used as defined in the PBR configuration. If no other route is present in the route map, the routing table is used.
An example of configuring PBR based on tracking object is shown below:
|//Configure and schedule IP SLA operations
ip sla 1
ip sla schedule 1 life forever start-time now
// Configure Object Tracking to track the operations
track 1 ip sla 1 reachability
ip access-list standard ACL
permit ip 10.2.2.0/24 10.1.1.1/32
//Configure PBR policing on the router
match ip address ACL
set ip next-hop verify-availability 10.3.3.2 track 1
set ip next-hop verify-availability 10.3.3.2 track 2 -> Track 2 is not shown here but it is used if track 1 fails
//Apply PBR policy on the incoming interface of the router.
interface ethernet 0/0
ip address 10.2.2.1 255.255.255.0
ip policy route-map PBR
The keyword “tcp-connect” enables the responder for TCP connect operations. TCP is a connection-oriented transport layer protocol -> C is correct.
The “num-packets” specifies the number of packets to be sent for a jitter operation.
The “frequency” is the rate (in seconds) at which this IP SLA operation repeats. The “tos” defines a type of service (ToS) byte in the IP header of this IP SLA operation.
When enabled, the IP SLAs Responder allows the target device to take two time stamps both when the packet arrives on the interface at interrupt level and again just as it is leaving, eliminating the processing time. At times of high network activity, an ICMP ping test often shows a long and inaccurate response time, while an IP SLAs test shows an accurate response time due to the time stamping on the responder.
An additional benefit of the two time stamps at the target device is the ability to track one-way delay, jitter, and directional packet loss. Because much network behavior is asynchronous, it is critical to have these statistics. However, to capture one-way delay measurements the configuration of both the source device and target device with Network Time Protocol (NTP) is required. Both the source and target need to be synchronized to the same clock source. One-way jitter measurements do not require clock synchronization.