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DOCSIS 3 Modems with Windows DHCP Server

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rmadmin
DOCSIS 3 Modems with Windows DHCP Server

I've run into this odd problem twice now, wondering if anyone else has seen a similar problem.

In both instances the following is common;
Problem only occurs with DOCSIS 3 modems regardless of manufacturer, but not DOCSIS 2 or older.
CASA CMTS using cable-helper (A 2200 and 3200)
Windows DHCP Server (Windows 2000, and 2003)

I have identical configurations with Linux DHCP servers that do not experience this problem.

Problem:
Cable modem in the example has a mac address of E83E.FC4D.5C81
The Windows DHCP server logs the following (And will not work unless we use the following mac):
10,12/02/13,13:06:06,Assign,10.0.0.10,,FC4D5C8100030001E83EFC4D5C81

Relevant debug from the CMTS:
----------Ether Protocol Packet----------
Dst Mac Address: ffff.ffff.ffff
Src Mac Address: e83e.fc4d.5c81
Type: IPv4 (0x0800)
----------IPv4 Protocol Packet----------
Version: 4
Header Length: 20
Type of Service: 0x00
Total Length: 541
Identification: 0
Flags: 0
Fragement Offset: 0
Time to Live: 64
Protocol: UDP (0x11)
Header Checksum: 0x78d1
Source Address: 0.0.0.0
Destionation Address: 255.255.255.255
----------UDP Protocol Packet----------
Source Port: 68
Destination Port: 67
Length: 521
Checksum: 437
----------DHCP Protocol Packet----------
Operation: Boot Request
Hardware Address Type: 1
Hardware Address Length: 6
hops: 0
Transaction ID: 618017105
Sencods Elapsed: 0
Flags: 0x0000
ciaddr: 0.0.0.0
yiaddr: 0.0.0.0
siaddr: 0.0.0.0
giaddr: 0.0.0.0
chaddr: e8 3e fc 4d 5c 81 00 00 00 00 00 00 00 00 00 00
sname:
file:
Magic Cookie: 63 82 53 63
Option:
Option 53(1 bytes)
DHCP Message Type: DHCP Discover
Option 60(10 bytes)
Vendor Class Identifier: 64 6f 63 73 69 73 33 2e 30 3a Option 61(15 bytes)
Client-Identifier: ff fc 4d 5c 81 00 03 00 01 e8 3e fc 4d 5c 81 Option 125(130 bytes)
Vendor-Identifying Vendor-Specific Information

The DHCP server appears to be getting the "Client Identifier" string... but why? And why only Docsis 3 modems?

kwesibrunee
Some DHCP clients send a DHCP

Some DHCP clients send a DHCP Client Identifier which contains an Identity Association Unique Identifier (IAID) followed by a DHCP Unique Identifier (DUID). In this case, the DHCP Client Identifier may begin with FF.
The DHCP client software may use terminology such as "enabling DUID" to refer to this behavior. In that case, reconfiguring the DHCP client software to "disable DUID" may cause the DHCP client to instead send the kind of DHCP Client Identifier we expect: a hardware type followed by a hardware address.

from here

dhcpd ignores client identifiers (linux) windows apparently uses them.

From MAC and Upper Layer Protocols Interface Specification CM-SP-MULPIv3.0-I23-131120

The CM sends a DHCPv6 Solicit message as described in [RFC 3315]. The Solicit message MUST include:
• A Client Identifier option containing the DUID (DHCP Unique Identifier) for this CM as specified by
[RFC 3315]. The CM can choose any one of the rules to construct the DUID according to section 9.1 of
[RFC 3315];
• An IA_NA (Identity Association for Non-temporary Addresses) option to obtain its IPv6 management address;
• A Vendor Class option containing 32-bit number 4491 (the Cable Television Laboratories, Inc. enterprise
number) and the string "docsis 3.0";
• A Vendor-specific option containing:
1. TLV5 option (reference [CANN DHCP-Reg] ) containing the encoded TLV5s describing the capabilities
of CM information option in Annex C.1.3.1;
2. Device ID option containing the MAC address of the HFC interface of the CM;
3. ORO option requesting the following vendor specific options:
a. Time Protocol Servers
b. Time Offset
c. TFTP Server Addresses
d. Configuration File Name
e. SYSLOG Server Addresses

So sounds like you are going to have to account for the DUID on docsis 3 modems or figure out how to not use client identifier on windows.

eivind
Windows DHCP, 3.0 modems MAC-problems

Maybe a little late, but it mighet help others...
Just copy the odd MAC-address from DHCP-log into W-DHCP-server reservation instead of writing the correct MAC. By saving the reservation You wil get a protest, but just ignore it. I have used this solution in several months and it gives no trouble.

juancitovera
Did you solve the problem

Hi rmadmin
Did you solve the problem with the dhcp and cable modem docsis 3.0 ?.
I have the same problem with a dhcp server mikrotik, any help will be grateful.

Thank you

docsis