According to my mod_perl quick reference card (reproduced verbatim):

$c = $r->connection;
$addr = $c->remote_addr( [$addr] );
$str  = $c->remote_host();
$str  = $c->remote_ip( [$ip] );
[download]

This is provided by the Apache::Connection class, although this documentation appears to contain what you want.

Hope that helps