gre = "{ 11.22.33.44, 99.88.77.66 }"
rdr on $ext_if proto 50 from $gre -> $ext_if
rdr on $ext_if proto 51 from $gre -> $ext_if
rdr on $ext_if proto 47 from $gre -> $ext_if

rdr on $ext_if proto 50 from any -> 10.0.3.253
rdr on $ext_if proto 51 from any -> 10.0.3.253
rdr on $ext_if proto 47 from any -> 10.0.3.253