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The CNA system needs to actively probe the internal VPN network/endpoint at regular (user-defined) intervals in order to measure packet transit times over each site-link.
The active probe mechanism requires that a device at your headquarters site (your VPN gateway or some other device) respond to a TCP connection, ICMP echo request, or an CNA traceprobe at regular intervals.
It's easiest to manage if the generic group command is used. It's very easy to add targets to a group and assign that group as the target within the active-measurement group. Enter the following command at the enable-level (config)# prompt:
group targets prefix 172.29.1.1/32 end
The name targets is just the name of the generic group. All prefixes designated with the /32 will be considered host endpoints for active-measurement groups.
Next you need to configure the active-measurement group to measure the target(s) in the generic targets group:
active-measurement group vpn-targets type icmp rate 4 per-minute timeout 3000 target group targets end
This active-measurement group chooses pings as the desired measurement type, configured at a rate of four measurements per minute (or once every 15 seconds). The timeout configured is 3000 milliseconds (or 3 seconds). And the targets to ping can be found in the generic group targets.
NOTE: In the example, both probes are configured to use the ICMP protocol. The CNA system allows you to choose between TCP, ICMP and traceprobes when you configure active probes. Some VPN implementations are may exhibit unstable behavior when multiple TCP sessions are opened and closed in succession to the same device, so Avaya recommends the use of ICMP probes or traceprobes whenever possible.
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