Bug 1268426

Description of problem:
We should document how to detect IPs in use on the provisioning network. Several deployments at customer sites have failed because it turned out that the discovery or host IP ranges already had IPs in use on the network.

Version-Release number of selected component (if applicable):
OSP-D 7 GA

Additional info:
Here is the content I am adding to the Network Reference Architecture:
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It is important to make sure that there are no IP conflicts on the Provisioning network. Perform a port scan on the Provisioning net from the Undercloud if you are not certain that the IPs used for discovery IP range and host IP range are free (replace the network in the nmap command with the IP subnet of the Provisioning network in CIDR bitmask notation).

######
$ sudo yum install -y nmap
$ nmap -sn 192.0.2.0/24
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For example, you should see the IP address(es) on the Undercloud, and any other hosts that are present on the subnet:

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$ nmap -sn 192.0.2.0/24

Starting Nmap 6.40 ( http://nmap.org ) at 2015-10-02 15:14 EDT
Nmap scan report for 192.0.2.1
Host is up (0.00057s latency).
Nmap scan report for 192.0.2.2
Host is up (0.00048s latency).
Nmap scan report for 192.0.2.3
Host is up (0.00045s latency).
Nmap scan report for 192.0.2.5
Host is up (0.00040s latency).
Nmap scan report for 192.0.2.9
Host is up (0.00019s latency).
Nmap done: 256 IP addresses (5 hosts up) scanned in 2.45 seconds
######

If any of the IPs in use conflict with the IP ranges in undercloud.conf, you will need to either change the IP ranges or free up the IPs before introspecting or deploying the Overcloud nodes.