can’t find domain controler from subnet

My Network has two phisycall subnets with a cisco router, 9.9.9.x and 172.16.254.x both with a 255.255.255.0 mask, my NT 4 sp6a PDC is in 9’s, every thig works fine since two weeks ago, my clients (98 & NT) in 172’s can’t find the Domain controler at logon time, i have a WINS server to. Any Idea