Hi, We're about to migrate our exchange to a /23 and we're likely going to do it over time. I have a simple filter in place to check and make sure that the NEXT_HOP is within our exchange's subnet. Originally it looked like this: function check_ixp_next_hop(ip nexthop) prefix ixpnet; { ixpnet = x.x.x.x/24; if ! (nexthop ~ ixpnet) then return false; return true; } And then within the inbound filter for each peer's ASN: if ! (check_ixp_next_hop(bgp_next_hop)) then reject; Since we're going to be caring about two distinct prefixes while we perform the migration, I changed the filter to look like this: function check_ixp_next_hop(ip nexthop) prefix set ixpnet; { ixpnet = [ x.x.x.x/24, y.y.y.y/23 ]; if ! (nexthop ~ ixpnet) then return false; return true; } However I'm getting the following errors in the log: 07-11-2013 12:33:00 <ERR> filters, line 61: ~ applied on unknown type pair 07-11-2013 12:33:00 <ERR> filters, line 61: ~ applied on unknown type pair 07-11-2013 12:33:04 <ERR> filters, line 61: ~ applied on unknown type pair Am I missing something? Thanks, -JJ