Set the stanza to have a server value equal to a comma-separated list of IP addresses and indexer ports for each of the indexers in the environment. This is explained in the Splunk documentation1, which states:
To enable automatic load balancing, set the stanza to have a server value equal to a comma-separated list of IP addresses and indexer ports for each of the indexers in the environment. For example:
[tcpout] server=10.1.1.1:9997,10.1.1.2:9997,10.1.1.3:9997
The forwarder then distributes data across all of the indexers in the list.

https://docs.splunk.com/Splexicon:Searchpeer
"A Splunk platform instance that responses to search requests from a search head. The term "Search peer" is usually synonymous with the indexer role in a distributed search topology..."

Splunk checks role-to-group mapping only during user login for external authentication (e.g., LDAP, SAML).
Users already logged in will continue using their previously assigned roles until they log out and log back in.
The changes to role mapping do not disrupt ongoing sessions.
Incorrect Options:
B:Search is not disabled upon role updates.
C:This is incorrect since existing users are also updated upon the next login.
D:Role updates do not terminate ongoing sessions.
References:
Splunk Docs: Configure user authentication

The possible causes of the load balancing issue on the Universal Forwarder are A and C. The receiving port and the DNS record are both factors that affect the ability of the Universal Forwarder to distribute data across multiple receivers. If the receiving port is not properly set up to listen on the right port, or if the DNS record used is not set up with a valid list of IP addresses, the Universal Forwarder might fail to connect to some or all of the receivers, resulting in poor load balancing.

https://docs.splunk.com/Documentation/Splunk/8.2.2/Knowledge/Usedefaultfields splunk_server The splunk server field contains the name of the Splunk server containing the event. Useful in a distributed Splunk environment. Example: Restrict a search to the main index on a server named remote.
splunk_server=remote index=main 404