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In order to receive randomly generated traffic from unknown users anywhere in the Internet (see Chapter 5: Configuring Agent-Based Measurement), your USTAT VIPs must have IP addresses that are generally unrestricted.
Active probes, on the other hand, require that the USTATs be able to receive TCP or ICMP reply packets.
If you don’t want to or can’t change your network policies to allow the USTAT VIPs to receive the TCP or ICMP reply packets required by an active probe, you can create a special purpose VIP for each USTAT.
If, for example, you load balance by direct server return, your network may drop traffic other than SYN packets; or, you may have configured your firewall to accept only traffic that has been initiated on the outside. Firewalls are sometimes configured to accept only TCP port 80/SYN packets.
The active measurement VIP allows you to configure your network to allow these active-measurement VIPs to be used for outgoing, locally initiated traffic only.
See the vip command in the CNA Command Reference Guide.
The CNA system will always use the active measurement VIP, if configured, for active probes. If there is no active-measurement VIP configured, the CNA system will use the standard VIP.
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