How to Uncap Docsis Compliant Cable Modems

7/17/2019 How to Uncap Docsis Compliant Cable Modems

1/7

How to uncap Docsis compliant Cable Modems


2/7

margin-top:12.0pt;margin-right:0in;margin-bottom:3.0pt;margin-left:0in;mso-pagination:widow-orphan;page-break-after:avoid;mso-outline-level:2;font-size:14.0pt;font-family:Arial;font-style:italic;}

h3{mso-style-next:Normal;margin-top:12.0pt;margin-right:0in;margin-bottom:3.0pt;margin-left:0in;mso-pagination:widow-orphan;page-break-after:avoid;mso-outline-level:3;font-size:13.0pt;font-family:Arial;}

h4{mso-style-next:Normal;margin:0in;

margin-bottom:.0001pt;mso-pagination:widow-orphan;page-break-after:avoid;mso-outline-level:4;font-size:8.0pt;mso-bidi-font-size:12.0pt;font-family:Verdana;}

a:link, span.MsoHyperlink{color:blue;text-decoration:underline;text-underline:single;}

a:visited, span.MsoHyperlinkFollowed{color:purple;

text-decoration:underline;text-underline:single;}@page Section1

{size:8.5in 11.0in;margin:1.0in 1.25in 1.0in 1.25in;mso-header-margin:.5in;mso-footer-margin:.5in;mso-paper-source:0;}

div.Section1{page:Section1;}

/* List Definitions */@list l0

{mso-list-id:1055161411;

mso-list-type:hybrid;mso-list-template-ids:-625158534 67698703 67698713 67698715 67698703 676

98713 67698715 67698703 67698713 67698715;}@list l0:level1

{mso-level-tab-stop:.5in;mso-level-number-position:left;text-indent:-.25in;}

@list l1{mso-list-id:1172792656;mso-list-type:hybrid;


3/7

mso-list-template-ids:-305369592 67698703 67698713 67698715 67698703 67698713 67698715 67698703 67698713 67698715;}@list l1:level1


@list l2{mso-list-id:1394769569;mso-list-type:hybrid;mso-list-template-ids:-2081504998 67698703 67698713 67698715 67698703 67

698713 67698715 67698703 67698713 67698715;}@list l2:level1


ol{margin-bottom:0in;}

ul{margin-bottom:0in;}

-->

How to uncap Docsis compliant Cable Modems

There are usually two network configurations. (1) The PC isdirectly connected to the cable modem. (2) The PC is connected to a NAT router,whose WAN port is then in turn connected to the cable modem. All of the followingsteps apply to both cases, except the final one that deals with TFTP. Illexplain the issues with this later.

Every time the cable modem is powered on, it looks in itsconfiguration file for the address of an TFTP server and for a file name. Thisfile is the Docsis configuration file that, among other things, sets a cap forthe modems download/upload bandwidth. The cable modem then retrieves that fileand connects to the backbone.

How do we uncap it? Simple. Well download the docsis configfile, edit it to change the cap parameters, then trick the cable modem in

thinking our PC is the TFTP server so it then retrieves our copy of the docsisfile.

Theres a bit of work involved for this. First, we have tofind out the TFTP server and file name used by the cable modem. For this we canuse the docsisDiag utility (http://homepage.ntlworld.com/robin.d.h.walker/docsdiag/docsdiag.zip).


4/7

This application, along with all others, is included in the CableUnCap.zipfile. Run docsdiag.bat. It uses SNMP to return many of the modemsparameters. Among these, the one we need are:

Configuration TFTP Server = 24.56.78.90 (replace this with yoursthroughout in the doc)

Configuration filename = isrr.bin (replace this with yoursthroughout in the doc)

And

IP fragmentscreated = 0

IPaddress.10.xxx.xxx.xxx = 10.xxx.xxx.xxx

IPaddress.192.168.100.1 = 192.168.100.1 (the IP address of the cable modem,(replace this with yours throughout in the doc)

IP-to-If-index.10.xxx.xxx.xxx = 2

This application works as is in many cases. If not, pleaserefer to the DocsDiag - DOCSIS cable modem diagnostics.htm file in thesame directory. It has a lot of help on how to make it work for differentmodems.

Note that you might now go to


5/7

>http://192.168.100.1and see some of you modems parameters.

Now from a DOS prompt type:

tftp -i 24.56.78.90 GET isrr.bin

You just downloaded the docsis configuration file from yourISP. Now its time to edit it to change the modems cap. This is done by usingthe Cisco Docsis configuration software in the docsisConfig directory (alsoavailable from http://www.cisco.com/warp/public/109/docsis_config2.shtml).Before running ConfigEdit.bat youll need to edit it and follow theinstructions contained there. Then execute ConfigEdit.bat and open the .binfile you TFTP'd. Go to the "Class of Service" tab. Voila'. Change theMax DS Rate to 7MB (mine doesn't seem to go higher). Save.

We will now need to have the cable modem think we are theISP and retrieve our version of the file by running our own TFTP server.

How?

This is the point where our network configuration isimportant. Here are the two cases. Both assume were running Windows 2000.

1.PC Directly Connected to Cable Modem

Configure your PCs TCP settingsfor:

IP: 24.56.78.90 (replace with the ISPs tftp server)

Netmask: 255.255.255.0

Gateway: 192.168.100.1 (replace with your cable modems IP address)

don't worry about the DNS...


6/7

When it's done change your TCPsettings to use DHCP again, without. Check http://192.168.100.1/or with the docsDiag utility. Your speed limit should now be updated.

2. PC NAT Router Cable Modem

Set your Router not to use DHCP butto use:


Netmask: 255.255.255.0

Gateway: 192.168.100.1 (replace with your cable modems IP address)

Youll now have to configure theRouter to send all traffic to your PC. LinkSys does this by configuring your PC

for the DMZ setting. Other routers may be different. All that should be neededis to either forward all external traffic to your PC or to make your PC visibleto the other side of the firewall.

Configure your PC with a static IPaddress in a range used by your router. Ex. If your router is at 192.168.1.1then configure your PC for:

IP: 192.168.1.100

Netmask: 255.255.255.0

Gateway: 192.168.1.1

Now add an additional IP address tothe TCP settings in your PC:


7/7


Netmask: 255.255.255.0

don't worry about the DNS...

This is done because youll have totell you TFTP server to listen on the latter address.

You shouldn't have to reboot. Place your modified copy ofthe isrr.bin (replace this with your name) in the tftpd directory (alsoavailable at ftp://ftp.ida.

net/pub/wireless/tftpd32.exe).If in your case the docsdiag showed it inside a subdirectrory you'll have tocreate one here. Start tftpd32 server. Go to Settings and set the Security toNone. Increase the timeout to 20secs and the Max Retransmit to 6. Choose totranslate Unix filenames. Make sure it's base directory point to where theisrr.bin is. Ok it. If you fall in case (2) make sure you set 24.56.78.90 IPaddress in the Server Interfaces.

Now power off the cable modem (I usually wait a few secondsjust to be sure) and then power it back on. After the traffic lights blinks thefirst time you should see that your tftp server is sending it your file...!

Now reconfigure your Router for DHCP (if case 2), and thenreconfigure your PC to DHCP.

Youre done!

Youll have to repeat this procedure every time the modem is

powered off.

How to Uncap Docsis Compliant Cable Modems

Documents

Transcript of How to Uncap Docsis Compliant Cable Modems