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Help understanding IP address


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#1 reaching

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Posted 06 June 2015 - 11:19 AM

I believe I have a public ip address.
It is in the following format:
74:xx:xx:xxx

I have dhcp enabled and automatic configuration enabled.


When I reset router/modem(power off then back on), the ip address does not change-why? Isn't it supposed to change whenever you reset the box? It's been the same for at least a week.

In the Ipconfig/all command, the IP address is listed as IPV4 and it has (preferred) after it. What does preferred mean? Preferred is listed after the different kinds of addresses in ipconfig.



I have windows 7 home premium operating system.


Edited by reaching, 06 June 2015 - 01:59 PM.


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#2 CaveDweller2

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Posted 06 June 2015 - 12:55 PM


 

When I reset router/modem(power off then back on), the ip address does not change-why? Isn't it supposed to change whenever you reset the box? It's been the same for at least a week.

 

That has to do with the way DHCP works. It just renews your lease. It would take incredible timing for 2 devices on their own to ask for an IP address or new lease on their IP addess at the exact moment to cause the IP address not to remain the same. If nothing really changes on the device requesting the IP address, normally the IP remains the same and the lease time is reset. But not always. In the past it seemed like I had a static IP from my ISP because it didn't change for the 2 years I was with that ISP.

 


 

In the Ipconfig/all command, the IP address is listed as IPV4 and it has (preferred) after it. What does preferred mean? Preferred is listed after the different kinds of addresses in ipconfig.

 

Just means that IP address has been verified as completely fine to use without restrictions. You can read about it here


Hope this helps thumbup.gif

Associate in Applied Science - Network Systems Management - Trident Technical College


#3 Nikhil_CV

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Posted 06 June 2015 - 01:07 PM

Some ISPs may bound IP lease with your modem/router/PC MAC address.

Also IP address lease can be custom set by ISP for a lease period of n days or hours (that too by ISP)

 

 

When I reset router/modem(power off then back on), the ip address does not change-why? Isn't it supposed to change whenever you reset the box? It's been the same for at least a week.

Power off then back on is not equivalent to resetting a modem. Its only powercycling the device.

May be ISP configured a saic IP for your connection?

 

[edited to fix typos]


Edited by Nikhil_CV, 06 June 2015 - 01:09 PM.

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#4 reaching

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Posted 06 June 2015 - 01:50 PM

Hello again guys,

                              Thanks  for responding.

 

I neglected to mention that the modem/router is one device-Technicolor from Time warner cable.  It functions as both modem and router but I do not have wifi so I assume the router part is disabled.  I can't get into router.

 

Everything in windows is set to automatic dhcp and automatic ip addresses. 

 

I have only been powering it off.  I have not reset it.  I thought powering off was resetting so thanks for clearing that up.

 

Oh and I'll start reading the link you provided.


Edited by reaching, 06 June 2015 - 02:02 PM.


#5 technonymous

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Posted 07 June 2015 - 11:19 PM

The ISP's dhcp server will remember your routers/pc's mac adddress unless something happens server side maintenance etc. It is possible to change it by changing the routers mac address from default to instead clone the first pc connected to the ports, or come up with a mac address to use. Over the years with working with computers I always had a pile of old nic card and dial modems sitting in the bone yard. I just use a mac from one of those. Just as long as it looks like a legit network device. Also not using a mac address someone else might already be using.


Edited by technonymous, 07 June 2015 - 11:20 PM.


#6 reaching

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Posted 08 June 2015 - 04:27 PM

Thanks Technonymous.

I keep reading about cloning Mac address but I'm not sure I am grasping the concept.
What I think I understand is every computer has a Mac address and it is used to determine the ip address. If you go in router settings (?) and change from a default setting to copy first computer that connects to Ports(meaning the first computer you plug in router?) then the ip will change according to whichever computer is plugged into router first.

Is that it? I'm probably overthinking this...
Does the router have a mac address different from the computer?
So, a modem has a Mac address too?
Which mac address am I using...the one from the modem?
Not sure what nic ....

My current situation is I am.dealing with a bridged modem/router...so it functions only as a modem. I just learned this. **smile**

#7 reaching

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Posted 08 June 2015 - 04:28 PM

Thanks Technonymous.

I keep reading about cloning Mac address but I'm not sure I am grasping the concept.
What I think I understand is every computer has a Mac address and it is used to determine the ip address. If you go in router settings (?) and change from a default setting to copy first computer that connects to Ports(meaning the first computer you plug in router?) then the ip will change according to whichever computer is plugged into router first.

Is that it? I'm probably overthinking this...
Does the router have a mac address different from the computer?
So, a modem has a Mac address too?
Which mac address am I using...the one from the modem?
Not sure what nic ....

My current situation is I am.dealing with a bridged modem/router...so it functions only as a modem. I just learned this. **smile**

#8 technonymous

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Posted 08 June 2015 - 09:32 PM

Yes, your modem, router, pc all have network interfaces to communicate. The modem has a mac address, but this mac address is used to identify the modem to the cable provider through the Cable Modem Termination System (CMTS) for the coax line. When you provision a modem they use the mac address in their system to identify your modem and account etc. As long as the COAX line is connected they can still communicate to the modem remotely, push a config, reboot it for troubleshooting purposes etc.

 

The first device that you typically connect to the modem is a router. A router has a mac address for both it's WAN & LAN network cards inside it. Connecting the router to the modem it gets the WAN IP from the ISP's DHCP server. Using the cloning the pc feature in the router is the same thing as if you plugged  the computer directly into the modem and bypassing the router. The cloning feature senses whatever wired pc is connected to it's local lan ports. However, you can program any mac address into the router and use that. It has it's uses.



#9 reaching

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Posted 09 June 2015 - 03:45 PM

Thanks so much for the detailed explanation, technonymous. It's beginning to become clear.

I am curious as to why one would want to clone Mac Address in the Router? I imagine so a computer can be discovered by another computer?

Also , I have old computers here. Would I be able to use one of their Mac addresses in the router? I imagine one would do that if they want to hide their computer.

I'm just guessing.

Anyway, thanks again for explaining the cloning.

#10 technonymous

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Posted 10 June 2015 - 02:31 AM

Different reasons...http://blog.technitium.com/2011/06/why-you-need-to-change-mac-address.html However, it can be used in nefarious way too.



#11 reaching

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Posted 10 June 2015 - 04:57 AM

Thanks for helping me to understand technonymous. I'll check out the link.




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