If the customer bind responder policy that refered http callout policy to ADC appliance global bind point. User's access to LB Virtual server will show blank page.

1. enable Health monitor for all callout service.
2. add SNIP with same netmask of default gateway in ADC.

Problem Cause

1. callout Service binded to callout Virtual server, the Health monitor incorrectly configured to OFF, which lead to callout virtual server status"UP". Actually, the backedn callout server is NOT reachable for ADC. Therefore, there are only Undef Hits, no Hits in show command output.

exec: show policy httpCallout
1)        Name: call_google_reCAPTCHA
Vserver: VS_google:443 (UP)
Effective Vserver state: UP
Return type: BOOL....
.
Result expr: HTTP.RES.BODY(1000).CONTAINS(": true")
Hits: 0
Undef Hits: 16
Last undef reason: Server is DOWN


2. After health monitor is enabled.The callout service status DOWN with ns.log printed error:  no SNIP avaliable to send the probe.
2866 Wed Sep 28 20:18:29 2022 MonServiceBinding_*:443_(tcp-default)(internal): DOWN; Last response: Failure - No MIP/SNIP available to send the monitor probe.

A normal callout policy performed as following:

ADC use SNIP to contact extra server(www.google.com here).

Meanwhile, if no SNIP/MIP provided to access to callout virtual server, packages captured shown as follows:

No package sent to extra server, and no response. About 30 second later, client FIN TCP connection.