The Cisco ASAv based AnyConnect SSL RA-VPN is solved by a DNS register? if the answer is yes, you have to delegate the register to the DNS listeners on the F5 DNS and create a listener with a couple of DNS pools to balance the traffic across both data centers, this is one example of the delegation that you have to configure:
Hope it´s work.
So i think you have to requirement for using GTM for Cisco ASA,
1. In case the customer would like to prefer site for support this service and another site for backup, you have to configuration load balance method "global availability" for prefer site
2. If the customer would like share load for Cisco ASA, So i think you have to using load balance method with raio or geolocation
I hope this information will help you
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