define at begining of kamailio.cfg "#!WITH_ANTIFLOOD", later add:

#!ifdef WITH_ANTIFLOOD
loadmodule "htable.so"
loadmodule "pike.so"

modparam("pike", "sampling_time_unit", 2)
modparam("pike", "reqs_density_per_unit", 16)
modparam("pike", "remove_latency", 4)
modparam("htable", "htable", "ipban=>size=8;autoexpire=300;")
#!endif

later routing definitions:

route[REQINIT] {
   if(src_ip!=myself) {
        if($sht(ipban=>$si)!=$null) {
            xdbg("request from blocked IP - $rm from $fu (IP:$si:$sp)\n");
            exit;
        }
        if (!pike_check_req()) {
            xlog("L_ALERT","ALERT: pike blocking $rm from $fu (IP:$si:$sp)\n");
            $sht(ipban=>$si) = 1;
            exit;
        }
    }
    if($ua =~ "friendly-scanner|sipcli|VaxSIPUserAgent") {
            xlog("L_ALERT","ALERT: friendly canings from $fu (IP:$si:$sp)\n");
        exit;
    }
    if (!mf_process_maxfwd_header("10")) {
        sl_send_reply("483","Too Many Hops");
        exit;
    }
    if(is_method("OPTIONS") && uri==myself && $rU==$null) {
        sl_send_reply("200","Keepalive");
        exit;
    }
    if(!sanity_check("1511", "7")) {
        xlog("Malformed SIP message from $si:$sp\n");
        exit;
    }
}