the devices as such cannot be configured to be in load balance mode or HA mode. If you want to load balance then you need to make use of a load balance server similar as shown here:
The appliances support DSR (Direct Server Return), a way of providing support for a light-weight load balancing, which can be enabled optional.
For HA both appliances can either run at the same time where traffic is primarily routed to one of the two via MX DNS priorites. So you would usually give the primary MX record the highest priority and the sendondary a very low one. Please note that this will not prevent mail servers from delivering messages to the secondary. Here is a sample from the Cisco MX's showing three different priorities from 10 to 30. In this scenario 10 would the one with the highest prioritiy.
cisco.com mail is handled by 30 aer-mx-01.cisco.com.
cisco.com mail is handled by 20 rcdn-mx-01.cisco.com.
cisco.com mail is handled by 10 alln-mx-01.cisco.com.
Otherwise its possible to have one appliance as cold stand by and switch it on in case the primary appliance fails.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...