Openstack fixed IPs and Floating IPs Part2

Openstack Fixed IP and Floating IP Part2

All screen-shots were provided from my current LAB "Openstack-Legacy router- 1 controller /1 network /2 compurte nodes"

Fixed IP is 10.10.10.20 while floating IP is 192.168.122.33 "Floating IP should be rout-able from outside network "

Here we can see our qrouter which will handle L3 operations including SNAT / DNAT . Now let us check how are our IPs represented in the qrouter . qrouter is just a network namespace in legacy Openstack will be implemented in network node . so let us get our namepsace

 Now lets list the interfaces inside it and see how our floating IP is represented beside our fixed IP subnet .

As shown here the interface connected to our fixed IP subnets is starting with qr and has ip from that subnet . 

qg interface has multiple IPs , we can notice IP 192.168.122.20/24 which will be used for SNAT PAT for instances without Floating IP. Second is our floating IP notice it's /32 . qg will handle all traffic going to outside but according to iptables SNAT rules inside the qrouter , the source IP will be changed either to 192.168.122.20 in-case of PAT and 192.168.122.33 in-case of Floating ip is existed . As below

As above any traffic initiated from 10.10.10.20 SNAT will change it's source to 192.168.122.33 "Floating IP " . While all other traffic going outside SNAT will change it to 192.168.122.20 .

Now in case of DNAT for floating IP

Conclusion in-case of floating IP SNAT / DNAT 1:1 happened . Unlike fixed IPs you don't need here complex DNAT or port Mapping .