Nagios plugins in distributed monitoring

Hi,

I have a distributed monitoring with 8 slaves and WATO disabled on the slaves. When I perform a nagios check like check_http, is the http check performed from the master or from the slave? When I specify an explicit host for the rule to apply to, who is performing the check? The master or the slave that monitors this host?
The thing is I would like to http check two origins from two slaves, so that each slave should perform the http check on both origins in case one slave is down.

The second thing is I tried to perform a keepalived_vrrp check with a self written nagios plugin, but it only works when I restrict the rocommunity to the master, regardless that the hosts running keepalived are being checked are monitored by a slave.

Just to have a correct understanding for the nagios plugins in check_mk.

Thanks a lot
Ghassan