I´ve solved my problem configuring a subnet for my interface on
/etc/dhcp/dhcpd.conf/etc/dhcp/dhcpd.conf:
# My interface subnet 172.20.19.20 netmask 255.255.255.255 { } **# My interface
subnet 172.20.11.0 netmask 255.255.255.0 { option routers 172.20.11.253; option subnet-mask 255.255.255.0; option domain-name-servers 192.168.20.251; range 172.20.11.10 172.20.11.100; option tftp-server-name "192.168.254.102"; }
subnet 172.20.19.20 netmask 255.255.255.255 { }**
subnet 172.20.11.0 netmask 255.255.255.0 {
option routers 172.20.11.253;
option subnet-mask 255.255.255.0;
option domain-name-servers 192.168.20.251;
range 172.20.11.10 172.20.11.100;
option tftp-server-name "192.168.254.102";
}