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What is floating IP??

asked 2016-12-18 13:45:03 -0500

vathanlal gravatar image

updated 2016-12-18 16:59:30 -0500


This is a general question about floating IP's. From my understanding floating IP's are set of IP's that is used by VM's to reach the external network like internet. Consider an example like I have 10 servers each with 128 cores. Total I want to run 1280 VM's at a time.. If all these VM's have to communicate with internet and accessible by users in external network whether I need 1280 different floating IP's or not??

In my current scenario my external network is in range and my physical router gateway is While creating virtual router I need to use the same gateway as the physical router right?? Then floating IP's should also be in range right?? Which IP will comes out of the virtual router to external interface?? Because I have other physical machines using IP in the same range..

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answered 2016-12-18 16:18:16 -0500

It's called floating IP, there is not "point" in the name. It's used for reaching instances from outside; instances can reach the outside world without floating IP. You can provide an address range when creating the external network in Neutron, as shown here

Read the install guide and the networking guide for configuration examples and for understanding the background.

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Oh sorry for the stupid mistake by me.. Ya Floating IPs.. But what I dont understand is whats the advantage of it?? As in the question if I have 1000+ VM's I need 1000+ floating IPs to access each of them from outside right??

vathanlal gravatar imagevathanlal ( 2016-12-18 17:05:40 -0500 )edit

You can access the floating IP address of a VM from outside. If your VM doesn't have a floating IP, which address would you use to access it?

Thus, the advantage of using floating IP addresses is that you can access VMs from outside.

Bernd Bausch gravatar imageBernd Bausch ( 2016-12-18 17:40:20 -0500 )edit

If all you need is access from your VM to outside, and you deploy the distributed virtual router, a floating IP may still be useful, as it prevents centralizing SNAT access from your VM. This is a rather narrow use case, I think.

Bernd Bausch gravatar imageBernd Bausch ( 2016-12-18 17:44:36 -0500 )edit

Thanks for the reply.. That means if I need 1000 VM's to be accessed from outside I need to reserve 1000 IP's for creating floating IP's for instances.. The thing is we can create any number of VM's but if it need to be accessed from outside we need floating IP..

vathanlal gravatar imagevathanlal ( 2016-12-19 06:22:04 -0500 )edit

This is true, but it's not limited to VMs. Anything you want to reach from the internet needs an internet address. That's why IPv6 was created.

Bernd Bausch gravatar imageBernd Bausch ( 2016-12-19 09:31:59 -0500 )edit

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Asked: 2016-12-18 13:45:03 -0500

Seen: 2,166 times

Last updated: Dec 18 '16