dhcp-routing

make DHCP become unicast with ONOS

DHCP: isc-dhcp-server
ONOS: 1.14
mininet: 2.2.1

1. DHCPsecond.py
   It creates two switches(s1, s2) and three hosts(h1, h2, dhcp).
   h1 and h2 link to s1.
   dhcp links to s2.
   h1 will get dynamic IP from dhcp.
   h2 has static IP.
   We can open wireshark on h2 to see whether h2 receives dhcp packets.
   

   Because it starts dhcp server by calling "dhcpd"(isc-dhcp-server daemon) to bypass namespace, we need to delete "dhcpd.pid" and "dhclient.pid" in /var/run or we can't start it again after closing it.
   Before starting it, we need to change the access right of "dhcpd.leases" in /var/lib/dhcp to 777.
   

2. dhcp-routing.json
   It tells the processor where dhcp is.
   

3. dhpd.conf
   It contains the configuration of dhcp server.