Problems in Assigning Ips to my Cable modem with DHCPd version 4.1.1 of ISC

Good afternoon friends.

I want to know if any of you have presented problems with the version of DHCPd version 4.1.1 of ISC Since I have a laboratory with it but it does not assign an ip address to my modem at the moment I have it configured in the following way. taking into account that I use a CISCO Ubr7240XVR.

The specifications of my server are>

Operating system CentOS Linux 6.5
Webmin version 1.680
Kernel and CPU Linux 2.6.32-431.el6.x86_64 on x86_64

# Red Base eth0 /// network of my server provisioning
subnet 172.17.0.0 netmask 255.255.255.0 {
deny client-updates;
deny unknown-clients;
range 172.17.0.100 172.17.0.105;
}
# Network CM-Cisco UBR 7246 // network of my cable modem
subnet 10.50.0.0 netmask 255.255.0.0 {
option subnet-mask 255.255.0.0;
option routers 10.50.0.1;
server-name "misa.balfate.hn";
next-server 172.17.0.1;
filename "noaccess.cfg";
deny client-updates;
deny unknown-clients;
range dynamic-bootp 10.50.0.10 10.50.255.254;
}
# cpe // my CPE network
subnet 172.21.0.0 netmask 255.255.0.0 {
option subnet-mask 255.255.0.0;
option routers 172.21.0.1;
option domain-name-servers 8.8.8.8, 8.8.4.4;
server-name "misa.balfate.hn";
deny client-updates;
allow unknown-clients;
range 172.21.0.10 172.21.255.254;
}

# CM-001 // modem provisioning.
host 10.50.0.10 {
filename "_25MB.cfg";
ethernet hardware 00: 25: F1: B2: 10: 5D;
fixed-address 10.50.0.10;
}