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Is there any way to determine if IPs are backed by actual VPSes? For example, a VPS host receives a /22 block of IPs. He puts them on his server and requests more, but you want to verify that each IP is being used to host an individual VPS and not just sitting on his host node. How can you do that?

I think each VPS would have a separate mac address.

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  • The MAC address isn't going to leave the switch the servers are plugged into, so that won't help you on the Internet.
    – Bert
    Aug 7, 2014 at 3:27
  • Why do you need to know? What you ask probably isn't possible. But if we know why you want to know that we may come up with alternatives.
    – Grant
    Aug 7, 2014 at 3:46

3 Answers 3

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This is not generally done by pinging or ARP trickery. It's done by paperwork.

Every request for IPv4 address assignments requires detailed justification, showing that existing addresses are fully utilized and that (in the case of ARIN) the new assignment will be 80% utilized within 30 days. See the ARIN Number Resource Policy Manual for complete details. RIPE and APNIC have similar policies.

The justification typically consists of a report stating what all of the existing IP addresses are currently used for, and how (and if applicable, for whom) the new IP addresses will be used.

The rules have been significantly tightened up in the last couple of years, now that IPv4 /8 blocks are exhausted.

On the other hand, you can give out IPv6 like free candy, and you should do so. Give everyone enough IPv6 subnets to last them for decades, and strongly encourage them to use their IPv6 allocations.

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You cannot do this. MAC addresses are only useful on Layer 2 networks. And besides, interfaces with multiple IP addresses do not need to have their own MAC.

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There is no way to tell for certain that each IP maps to a different server.

If you are on the same LAN you can use most IP scanning tools (or ping them and look at your ARP table) to match the IP addresses to network cards. But that still doesn't mean unique servers (virtual or physical), since you could add 20 network cards to one VPS.

Even worse, they may all map to the same MAC address if the host machine does NAT for the virtual machines. Same if there is a firewall between you and them (which could be something like a pfsense virtual machine on the host).

If you are not on the same LAN, MAC addresses are right out and you don't get any clues as to where they go. You can't even tell if they are really used or not - unused ones may be configured on a NIC anyways. Used ones may not respond to any ping or port scan.

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