imtiax Premium Member join:2014-05-24 Toronto, ON 2 edits |
imtiax
Premium Member
2014-Nov-2 9:12 pm
IP Assignment QuestionHi. I do some stuff online that requires me changing my ip address a few times daily (I know it sounds suspicious/odd but I can assure you it is nothing bad). Back when I had the non home gateway modems ( Motorola SB5101 ) a few years ago, and my computer directly attached to the modem via ethernet. Simply spoofing the mac address with a simple software like this » www.technitium.com/tmac/and doing ipconfig/renew would change my rogers public ip address within seconds. -- What has been annoying me ever since they required me to get one of those home gateway modems is that tossing it into bridged mode doing the stuff I mentioned above, only works upto 2 times. It seems as though Rogers assigns 2 public ip addresses to each modem, and they wont change unless a hard reboot is performed along with a mac address change. Why is this? If I bought my own Motorola SB5101 and got rogers to provision it for me, would I run into the same 2 public ip address issue, or would it bypass that? |
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Just buy a router that what i did and then change the mac address |
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imtiax Premium Member join:2014-05-24 Toronto, ON |
imtiax
Premium Member
2014-Nov-2 10:16 pm
Yeah I just tested it with my ASUS RT-66NU. I changed the mac 2 times and it gave me 2 different ip addresses.
The 3rd time it wouldn't assign me a new ip until I hard reset the modem. |
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yea same with me |
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GM85Click, Click join:2002-07-02 Canada 1 edit |
to imtiax
That's interesting that you were able to change the MAC address and able to obtain a new ip with the sb5101.
I previously also had the sb5101 (and still do on my internet connection at work). Both adhered to the 1 active MAC address restriction and had to be rebooted whenever i replaced my router or MAC address.
If you were able to change the MAC and obtain a new IP without rebooting the sb5101, i would say that you were in a unique situation and that your modem wasn't properly provisioned.
Unfortunately if you were to replace your current modem with a sb5101, my guess is that it would also have the 1 MAC address restriction.
Ive heard others say the new combo modems (like you mentioned) have a 2 MAC address restriction. Not sure why they bumped it up.
Edit: The reason for the MAC address restriction was they didn't want you to attach a switch to your modem and obtain public IPs for all your computers. Thats the reason why the modem "locks" onto the first MAC address it sees. I think Rogers used to provide additional addresses for $5 / month. |
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your moderator at work
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HiVolt Premium Member join:2000-12-28 Toronto, ON |
to imtiax
Re: IP Assignment QuestionIf you require an IP change several times a day, it's best you switch to DSL/VDSL. Its PPPoE dynamic IP is changed as soon as you hit the disconnect/reconnect button in your router, and you get a different one EVERY time.
The DHCP system on cable is not quite as user friendly with regard to this, as changing NIC/Router MAC addresses will only work a couple times then your Modem MAC gets blacklisted for a period of time. |
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If it used to work for you, it sounds like the dhcp server is just operating differently than it used to. What you are describing sounds like normal operation at this point.
You'll get an IP, change mac, get a 2nd IP, then you're going to have to power off / on the modem to be able to pull a 3rd. There is a limitation in the cable modem config file of 2 active devices requesting DHCP through the modem. Power off/on typically resets that short list of 2 devices in the modem and you get a fresh 2.
At some point the rogers DHCP server is probably going to black list you if you're pulling lease after lease.
As HiVolt said, dynamic DSL would be much more effective for you. Or maybe a proxy/vpn solution of some sort. |
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JC_ Premium Member join:2010-10-19 Nepean, ON |
JC_ to imtiax
Premium Member
2014-Nov-4 7:47 pm
to imtiax
said by imtiax:If I bought my own Motorola SB5101 and got rogers to provision it for me, would I run into the same 2 public ip address issue, or would it bypass that? They won't provision it for you, Rogers has moved to all Docsis 3 modems. |
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sbrook Mod join:2001-12-14 Ottawa |
to imtiax
Beware that it's the MAC of the first router or system behind the modem that must change. (A gateway in gateway mode, unless you can actually get to the interface that will change its MAC won't work)
You have to do an IP release before you change the MAC otherwise you'll hit the IP address limit. |
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said by sbrook:You have to do an IP release before you change the MAC otherwise you'll hit the IP address limit. hrm, does a dhcp release get recognized when it comes down to the cable modem cfg file limiting to 2 attached devices? ie. modem sees 2 devices, dhcp release reduces that to 1, and then mac clone, renew dhcp, and modem sees 2 again.. Or are you referring to the external dhcp server side? |
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sbrook Mod join:2001-12-14 Ottawa
1 recommendation |
sbrook
Mod
2014-Nov-5 11:24 am
Gotta understand the DHCP process here. It's nothing to do with the Cable Modem config file. What you are seeing at the modem is a report of the number of allocatable IPs. The modem doesn't limit the IP allocation. That's done by the DHCP server.
When you make a DHCP request, it is relayed through the CMTS. The CMTS recognizes the source as the MAC *of your cable modem* and tags that into the DHCP request and then relays it to the DHCP server.
The DHCP server looks up in its tables that MAC address. The tables will contain entries for the max number of IPs available to assign and the IPs currently assigned. Typically the max is 2 and the examples below assume 2 max.
So, if there are 0 currently assigned, it will assign the first and record it in the table If there is 1 currently assigned, it will assign a second and record it. If there are 2 currently assigned it will refuse the request.
If you do a reverse lookup of an assigned IP from a cable customer, you may find an address that looks like ...
CM12A5C413-CP34AB2323.cable.rogers.com
(the IPs are rearranged so often, the reverse lookups often don't work)
The CM number is the cable modem MAC. The CP number is the MAC of the device wanting an IP address which is sent in its DHCP request. (CP short for Customer Premises Equipment - your computer is direct connected, or your router if not.
When you request an IP you actually do an IP renew on 0.0.0.0 which the server treats as a new request.
So, you should be able to see how, without releasing any current IPs, how you can get only 2 IPs assigned at any one time.
Now a release says "I no longer need this IP (xx.xx.xx.xx) associated with this CPE device" and the CMTS throws in "and with this CM device". So the DHCP releases the IP back to the pool of available IPs.
Now there is also a list of "recently assigned IPs" for a given CP-CM combination. SO if you release the IP and then do a new request, the CMTS looks at the recently assigned, checks the availability and will reassign the old one if available! This is why it seems the IPs are sticky!
So, the way around this stickiness is to change the MAC (of the CPE). BUT if you don't release the previously assigned IP, it is treated like a brand new device requesting an IP, so the DHCP server says "You've got 2 devices already connected and 2 IPs ... Request denied!"
Now remember I said that the IP is sticky. Sometimes when you release an IP it goes back to the pool, even if you then CHANGE the MAC, and request a new IP, you can actually STILL end up with the same IP pulled out of the pool! This depends on availability in the pool.
Does that help you understand what's going on? |
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3 edits |
It does. When messing with mac cloning in a router, I've never 'released' the lease. Unless there is a dhcp release triggered when doing a software reboot in a router.
So in practice, my router has an IP lease. I change the mac, router reboots, and I get a 2nd lease, new IP. Then if I change the mac again/reboot router only, I get a DHCP timeout, no new lease. Power off/on the modem, and I get a new (3rd) DHCP lease. Change mac again, I get a 4th. Change mac again, timeout, power off/on modem, and I get a 5th lease.
I guess that behavior made me think that modem config file and interface saying "computers allowed by service provider: 2" was a limit configured right into the modem side of the equation. Why does the modem reboot change anything with all limits being server side? Is it just a matter of some time going by before the modem is back on and the router tries to pull a lease again?
In theory then, if I'm not being dense, if I were to do a DHCP release in the router, and change mac, I would not keep hitting limit of 2 and need for powering off/on the modem?
-making the assumption that the DHCP server isn't going to blacklist for excessive DHCP requests -also all of the above is based on bridge cable modem and separate router |
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sbrook Mod join:2001-12-14 Ottawa
1 recommendation |
Rebooting the modem tells the CMTS that the modem has gone away, so it tells the server to delete ALL IPs associated with that Cable Modem's MAC. SO, you simply start all over.
Sometimes the CMTS doesn't notify the DHCP server if the restart is soon enough. |
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