Someone elses public IP used as private IP

[jofinjoseph]

Hello,

I have this customer who use a public IP address range(for example, 100.100.100.0/24) in their internal LAN. They have assigned these IP address to servers, laptops, printers etc. And these are NATed(PAT) to firewall outside interface IP when the traffic go out. The 100.100.100.0/24 is actually assigned to another company in another country. My customer just use it like a private range.

Can you please let me know what are the risks continuing like this ? How can I convince the customer to change the LAN IP to private IP address.

Thanks

Jofin

[zdesignstudio]

Not best practice.

Doesn't scale.

You will never be able to talk to the real outside address.

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[DerrickCrump8635]

I agree.  This is not a best practice and should be avoided at all costs.  I too had client who did the same exact thing.  This creates problems when communication is needed beyond the local LAN.  If you have not, begin to devise a plan to migrate them from that public IP space to a different block that is public, but that is exclusively theirs.

[paul driver]

Hello

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@jofinjoseph wrote:

Hello,

I have this customer who use a public IP address range(for example, 100.100.100.0/24) in their internal LAN. They have assigned these IP address to servers, laptops, printers etc. And these are NATed(PAT) to firewall outside interface IP when the traffic go out. The 100.100.100.0/24 is actually assigned to another company in another country. My customer just use it like a private range.

Can you please let me know what are the risks continuing like this ? How can I convince the customer to change the LAN IP to private IP address.

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As long as this subnet doesn't get leaked into the public domain then all is good you can use whatever ip range you desire, but it is suggested to use the RFC1918 range of addressing for internal host assignment.

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16