Primary - Dell N1100-ON Reference Manual

Note that, when multiple RADIUS servers are configured with different
names (for example, ServerName is name1 and address is 1.1.1.1 and
ServerName is name2 and address is 1.1.1.2):
The RADIUS request is always sent to the first ordered name server list, i.e.
name1 server list would be tried before moving on to name2. Even if the
priority value of servers in name2 is lower (lower value indicates high priority)
the request would be sent to the name1 servers. If for name1 list, the
configured servers fail to respond, the request is sent to the second configured
name list.
Within the same server list, the first primary server would be tried. You can
have multiple secondary servers in the same name list. From the multiple
secondary servers, the one with the lowest priority value would be tried. For a
different named server list, the server name would be based on lexicographic
order. For example, if name9, name1, name6 are configured in this order,
name1, then name6, then name9 would be tried.
Example
console(config)#radius-server host 44.44.44.44
console(config-auth-radius)#name NAME
console(config-auth-radius)#no name

primary

Use the primary command to specify that a configured server should be the
primary server in the group of authentication servers which have the same
server name. Multiple primary servers can be configured for each group of
servers which have the same name. When the RADIUS client has to perform
transactions with an authenticating RADIUS server of the specified name, it
uses the primary server that has the specified server name by default. If it fails
to communicate with the primary server for any reason, it uses the backup
servers configured with the same server name. These backup servers are
identified as the "Secondary" type.
Syntax
primary
Default Configuration
There is no primary authentication server by default.
919
Security Commands