When is Network Address not unique?

Question

Can there be any situation when network addressess are not unique?

Answer 1

Hi Maddy, I am just learning this stuff so I am pleased to have an opportunity to write down what I know so far. I know that all TCP/IP protocol addresses HAVE to be unique in order to properly connect on the Internet. Now, it is true that within a LAN private addresses are often used which are also used by other, spererate LANs, not connected to the same network. However, there still is required for the network to have one IP address which is public, which the world communicates through to reach each privately networked computer. There IS a situation where a network can have addresses which duplicate other addresses, however this is only on a network which has no connectivity with the outside world Internet Network. It is a private LAN with no connectivity with any network outside its own ifrastructure. This could create serious issues if it then was put "Online" with the public Network, in which the addresses then are duplicated and the Network Admin would be forced to change each private address to a public address OR to provide ONE IP address through which all other private addressed computers communicate to the outside public Internet, OR even to another private network. It is vital that each computer directly connected to the world wide public network have a unique address or identifier.

This is a often misunderstood protocol as it is so complicated, which causes a lot of misunderstanding of how it works. However, one point is very simple: Each individual computer accessing the world wide Network, called the Internet, MUST have a unique identifier, and today the TCP/IP Protocol is fast becoming the universal network protocaol wuite due to scalability and its role adn an internet standard. (I just copied that last sentence from the Windows XP Professional Resourse Kit). ;-)

So, each of the other respondants are correct, but have a portion of the picture as a whole. This is the sum total of my current understanding of how public, private and static IP addressing works and why it is now a universal standard in todays Internet Protocol. Of course the nuts and bolts of this are very intricate and very confusing. A person who is not 100% confident in ability to manually configure these items should leave it alone.

I think you know the answer to this question already Maddy. :-)
I am learning as quick as I can, and it gets really confusing when you start looking at Domains and using Server OS software. Boy is it ever a complex and difficult item to learn. I have a wireless network which uses a built in DHCP server, a DNS protocol, and Automatic private address assignment. Thank Goodness!!

So, to sum what I know up, there is NOT any situation when network addresses are not unique. While individual private networks may use addresses other private networks also use, they do not qualify as a duplication as each network is an individual and seperate entity. An individual and seperate network entity does not have any relation or affect on another seperate and individual network entity. When networks are connected they must have at least one computer which has a unique IP address or connectivity fails. When private networks connect to one another, and then around the world to the public network each private network connected to the public network HAS to have one computer with a unique address through which the remaining computers with private address conect through to the public network. So, no, there is not a time when network addresses connected to the world wide network is not unique. Inside the private networks each computer has to have a unique address to connect to each other. While these private addresses can be duplicated in other private networks, they simply do not have any relationship to one another as each is private and seperate networks. Once these private networks connect to even one seperate network they have each have to have one unique address that each private network uses to maintain communication with each other. While the computers behind the prublic addresses can be indentical to those within the network behind the other public address the two networks have to have that one public and completely unique address to have connectivity with each other.

Ok, this is the best I can do! lol
Thanks for the question as it provides a way for individuals like me can formulate new information into a cohesive dialog which then allows for the information to assimulate more completely, which creates a unique manner of increasing understanding of the material and cementing that knowlege. If I have any mistaken understanding of this issue please let me know so I don't continue to assimulate wrong information.

Thanks Maddy, have a great day!

Answer 2

Okay by Network address I'll assume you are talking TCP/IP.
Yes but not in a correctly designed network.
I can think of two scenarios from memory that can cause this-
1. a network admin statically assigns the same IP address to two machines. this breaks arp tables and confuses the hell out of many services.
2. the DHCP server fails or 2 DHCP servers are on line. This is quite common in many small business networks that attempt to configure their first server. Generally your DHCP server will be a network server and be configured from that. Smaller networks buy routers with DHCP already configured. When a client boots up it sends a broadcast request that both DHCP servers will answer (unless it has an active registered lease and the client is aware if it) If the DHCP (Server or router)1 has the same scope as DHCP 2 you can duplicate ip address.
Many times the client machines will find this out and show an error.
I hope this helps.

Answer 3

if they're manually assigned then any number of computers can have the same network address within a local area network. this would obviously cause problems because more than one computer with the same address cannot be on the same network.

this is why dhcp is popular, because it gets rid of the need to manually issue, and keep track of, ip addresses and instead automatically gives out unique network addresses to all computers on the network.

Answer 4

Sure but the network will more than likely encounter problems, thats why in alot of LANs people use private ip addresses, to provide themselves with more addressing if they need it. This also saves money so you do not have to pay for another ip address. You can referren rfc 1918 on what a private address is.