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A newbie needs help...

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A newbie needs help...

Hello to everybody,

I am a technician for TCP/IP networks. Now my CEO gave me a new project. I should plan, configure and operate a cable network. I got a miniCMTS LMC-2IU (www.minicmts.com) and two kinds of CMs. There are a CISCO EPC3928AD and a CISCO EPC3208. Both should work. With the help of this forum I got the Internet side working.
But now to my problem. I could not get working the MTA modules. There are a couple of problems.
First I haven’t the MTA MIBs for my CMs. Second the MTA does a DHCP request, the DHCP make an offer, but there is no acknowledge and the MTA got no IP.
I think the DHCP configuration isn’t ready to work, but I have no more idea and my knowledge in this field isn’t so good. If somebody could take my by the hand and show me my failures, I would be very fortunate.

Please let me know what you need to help me.


Show Us Your DHCP config

Show Us Your DHCP config



First of all - you've got quite a task ahead of you setting up a DOCSIS network if you have limited previous knowledge in that field... Good luck!

1 - Routing may be an issue (as always when a DHCP server sees DISCOVER, sends OFFER but no REQUEST is seen by the DHCP server). If you can ping the MTA GW IP (the cable (!) interface of the CMTS that the MTAs are supposed to use as their gateway), you should be fine. Normally, I'd have a separate IP subnet for MTAs on the cable side. Perhaps you don't.

2 - If the MTAs sees a DHCP OFFER from a DHCP server it doesn't recognize, the offer will be rejected. Should be noticed in the logs of the modem (or not, some modems are pretty picky about what they report). If you have a proper setup with all DHCP options the MTAs require, you may have forgotten the option "docsis-mta.dhcp-server-1" (code 1 below, you may have a slightly different name for it in you dhcpd.conf).

3 - The other options I mention below are alos needed, but I don't think they are in this stage.

4 - This was just a quickie from my side of the pond - others may pitch in here :)

option space docsis-mta;
option docsis-mta.dhcp-server-1 code 1 = ip-address;
option docsis-mta.dhcp-server-2 code 2 = ip-address;
option docsis-mta.provision-server code 3 = { integer 8, string };
option docsis-mta.as-req-as-rep-1 code 4 = { integer 32, integer 32, integer 32 };
option docsis-mta.as-req-as-rep-2 code 5 = { integer 32, integer 32, integer 32 };
option docsis-mta.krb-realm-name code 6 = string;
option docsis-mta.tgs-util code 7 = integer 8;
option docsis-mta.timer code 8 = integer 8;
option docsis-mta.ticket-ctrl-mask code 9 = integer 16;
option docsis-mta-pkt code 122 = encapsulate docsis-mta;

shared-network C4cMTAsubnet {
option docsis-mta.dhcp-server-1;
option docsis-mta.provision-server 0 "\003mta\004test\003net\000";
option docsis-mta.krb-realm-name "\005BASIC\0011\000";
subnet netmask {

This may need a bit of explaining:

option docsis-mta.provision-server 0 "\003mta\004test\003net\000";

\003 means 3 characters follows, namely "mta" in my case
\004 means 4 characters follows, namely "test" in my case
\003 means 3 characters follows, namely "net" in my case
\000 means end of string (end of option)

If your provision server string is different (well, it should be :) ), your numbers will vary:

option docsis-mta.provision-server 0 "\008mta-test\006domain\002se\000";

Simple when you know it...

Best of luck!



Hello Fredrik,

thanks for this guide. You helped me a lot. And now I understand something more…
Yes I can ping the MTA GW IP. I am very happy about this. ;-)
But now I have some questions:

1. For what do I need Code 7, 8 and 9? And what is this?
2. Must there be a log server?
3. Must code 3 (provision Sever) be a FQDN or could it be an IP?

Ok this is it for the moment.


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