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[netmation]

I am in a shared office building where I am paying for a STATIC IP address. They gave me an internal 19x.xxx.xxx.xxx IP address for this. And said that if I am external to the building I should use the external address 75.xxx.xxx.xxx. Is this typical that I would not have a single static ip address that could be used both externally and internally to the building and network? Or is this how it needs to be setup?

[EddieZ]

the 19x.xxx.xxx.xxx are internal IPs'which can only be addressed from the inside of the LAN.

The building has one external IP (75.xxx.xxx.xxx, the connection with the outside world through the ISP), which is shared by the building by means of a switch that gives everybody inside of the building an internal LAN IP. These can also be distributed dynamically but if you need to pay more for a fixed IP you're being conned. So you are all sharing one subscription and you do not have a subscription dedicated to yourself.

[netmation]

The external IP I mentioned is not shared by the building.  That is what they gave me specifically and mapped it to my internal static IP.  Is this normal procedure, I have not seen this before.  Why can't I just have the same IP for external to the building and internal to the building?

[Fatman]

I think what netmation was trying to convey is something like the below.

Int: 19x.xxx.xxx.yyy
Ext: 75.zzz.zzz.yyy

Where the x's don't match the z's but the y's probably do and his building is 1 to 1 NAT'ing that external address to that internal address.

This is shady, if your paying for a public static, they should route that bad boy to you, not NAT it to you.  This makes management a pain and is a potential security concern depending on whether you trust your building ITs.  It would appear to me that you either have a inexperienced or unscrupulous building IT department.

To make this simple and avoid overstepping my bounds, I would never pay for a ISP who provided me a non-routable IP.  PERIOD.  This is doubly true if I am paying for public static(s) IP(s).  Then again I am of the technocrati and not everyone is so picky, but I think they should be.  If a ISP does this it is a sure case they have a captive customer base (as it sounds like the case is here and everywhere I have heard of such gimmicks), as no one pulls this off in the wild for long.

[netmation]

Thanks for the info FATMAN, you understand the situation.  Could you help me understand why the IT department would want to do this?  What disadvantage is in it for me having it setup this way other then the inconvienience of not being able to use my external IP inside the building?

The other issue that came up is that they are telling me if my MAC address changes on my router, like plugging in a new device my internal Static IP would get's reassigned.  Does this make any sense?  Why would a static IP address ever drop my office as (i.e. router) no matter what I plug into it?

[EddieZ]

The IP is probably linked to your MAC address.

Sorry if I did not understand your situation, use the extended alphabet next time. 

[Fatman]

Here's the deal, you need to work this out with them as my post below is based entirely on the way I read a situation where I don't have all the facts.  A less paranoid person might see nothing so alarming as the below.

Could you help me understand why the IT department would want to do this?

Well, this anwser is based mostly on supposition, as I can not think of any legitimate reasons.

They don't know how to route the public IPs properly or do not have the routed infrastructure to do so.
They think they know best and are applying their own security practices at the NAT level.
They find it easier to assign a public IP by DHCP than manually configuring and assigning one for each new tenant.
They take the BOFH handbook seriously.

What disadvantage is in it for me having it setup this way other then the inconvienience of not being able to use my external IP inside the building?

The option above that bothers me the most (and applies to your question) is that they might be deciding what traffic should and should not be passing.

It could be ports blocked, or SPI checks, or some level of IDS/IDP.

None of it belongs in a position where they can restrict your use of your connection.

Given they are performing NAT for you, some level of specific configuration had to go into these issues, they couldn't avoid having to touch on these subjects.

Best of all, they might not even be aware that they are doing it, and proving it will be annoying if they are defensive about it.

The other issue that came up is that they are telling me if my MAC address changes on my router, like plugging in a new device my internal Static IP would get's reassigned.  Does this make any sense?  Why would a static IP address ever drop my office as (i.e. router) no matter what I plug into it?

Are you pulling your internal static via DHCP?  This is the option that falls into my theory of ineptitude and lack of ability or will to assign and configure statics.  This would imply to me that they have a block of IPs and some static port forwards and are just letting anyone have any IP (this is not a public static).

If you had to manually assign this internal address then it sounds like they are trying to lock you down with ALGs, which points to them being competent, but less than ethical.

[DCIFRTHS]

I am in a shared office building where I am paying for a STATIC IP address. They gave me an internal 19x.xxx.xxx.xxx IP address for this. And said that if I am external to the building I should use the external address 75.xxx.xxx.xxx. Is this typical that I would not have a single static ip address that could be used both externally and internally to the building and network? Or is this how it needs to be setup?

Are you renting office space, and paying for this static IP address yourself, or do you work for an employer that is paying for the office, and the static IP address?

[Fatman]

Are you renting office space, and paying for this static IP address yourself, or do you work for an employer that is paying for the office, and the static IP address?

That's the 64K(b) question.