LinuxQuestions.org - Pxe Server Stopped Working!

I have a linux pxe server that servers the 172.26.129.0 and 172.18.207.0 networks. The linux pxe server is physically on the 172.26.129.0 network. An ip helper is used on the the gateway router for the 172.18.207.0 network to forward udp rquest to the linux pxe server. Well this week the server stopped working. I checked /var/log/messages and I keep getting continual BOOTREQUEST from the 172.26.158.1 gateway. Someone has set a ip helper to forward udp request to my subnet. Is there a way to block theses request with tcp-wrappers or iptables? My dhcpd.conf doesn't issue dynamic addresses. IP addresses are set statically to bind to particular ethernet addresses . Also, I only have the 172.26.129.0 and 172.18.207.0 subnets defined in dhcpd.conf.