Using Option 43 Info FROM a Cable Modem Client to Define a Class
Glenn Satchell
Glenn.Satchell at uniq.com.au
Tue Oct 16 12:29:02 UTC 2007
>Subject: RE: Using Option 43 Info FROM a Cable Modem Client to Define a Class
>Date: Mon, 15 Oct 2007 16:32:02 -0400
>From: "Perry, Keith" <Keith.Perry at sciatl.com>
>
>The option I'm trying to filter on is always placed first by our client
>so I'm too concerned with reliability. I already reviewed the
>application section of the dhcp-options MAN page prior to sending out my
>initial request. It is solely about setting sub-options to provide to
>the client - nothing about reading sub-options from the client. I've
>tried the 5 variations below with no success. Conf file passes syntax
>check with any of these:
>
This looks for the string "ECM" starting at the 6th character in the
string. Remember first position is 0.
>match if substring (vendor-encapsulated-options, 5, 3) = "ECM";
This looks for "ECM" starting at the fourth character:
>match if substring (vendor-encapsulated-options, 3, 3) = "ECM";
This looks for the string "45:43:4d" - you need to leave out the quotes
to get hex chars, ie 45:43:4d
>match if substring (vendor-encapsulated-options, 5, 3) = "45:43:4d";
>match if substring (vendor-encapsulated-options, 3, 3) = "45:43:4d";
This one would work without the quotes...
>match if substring (vendor-encapsulated-options, 0, 5) =
>"02:03:45:43:4d";
This was the value in the string as reported by the packet sniffer below:
Value: 020345434D030845434D3A4553544204095341424A4E425A...
It is pairs of hex characters, so in dhcpd format it would be:
02:03:45:43:4D:03:08:45:43:4D:3A:45:53:54:42:04....
So, 02 is sub-option 2, 03 is length of the option, 45:43:4D is the
value stored in the sub-option, in this case the ascii codes for E, C
and M. Next 03 is sub-option 3, 08 is length, value is the next 8
bytes, and so on.
Remember that for sub-string() you count the starting position from 0,
so I believe the match line becomes
match if substring (vendor-encapsulated-options, 2, 3) = "ECM";
or
match if substring (vendor-encapsulated-options, 2, 3) = 45:43:4D;
HTH. By the way, the packet dump was really useful for working this out.
regards,
-glenn
--
Glenn Satchell mailto:glenn.satchell at uniq.com.au | Some days we are
Uniq Advances Pty Ltd http://www.uniq.com.au | the flies; some
PO Box 70 Paddington NSW Australia 2021 | days we are the
tel:0409-458-580 tel:02-9380-6360 fax:02-9380-6416 | windscreens...
>But fails to place the embedded CMs in the pool I have specified below:
>********************************************************************
> # Cable Modem Subnet
> subnet 10.5.128.0 netmask 255.255.192.0 {
> pool {
> range 10.5.128.1 10.5.128.250;
> filename "CM.cfg";
> deny members of "embeddedCM";
> deny dynamic bootp clients;
> }
> pool {
> range 10.5.129.1 10.5.129.250;
> filename "embeddedCM.cfg";
> allow members of "embeddedCM";
> deny dynamic bootp clients;
> }
> option subnet-mask 255.255.192.0;
> option routers 10.5.128.254;
> option broadcast-address 10.5.191.255;
> option time-offset 19800;
> option time-servers 10.253.0.10;
> option log-servers 10.253.0.10;
> next-server 10.253.0.10;
> authoritative;
> }
>********************************************************************
>
>I'm beginning to wonder if the server only handles outbound Option 43
>info and not inbound ?
>
>
>Regards,
>
>Keith
>
>
>
>-----Original Message-----
>From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On
>Behalf Of Glenn Satchell
>Sent: Friday, October 12, 2007 6:52 PM
>To: dhcp-users at isc.org
>Subject: Re: Using Option 43 Info FROM a Cable Modem Client to Define a
>Class
>
>Hi Keith
>
>You may not find the substring function reliable in this situation as
>the device is allowed to include the sub-options in any order. The
>dhcp-options man page has a section titled "VENDOR ENCAPSULATED
>OPTIONS". This is mostly about setting the sub-options, but should give
>you the information needed to decode them as well. It describes the
>format, which is the sub-option number, length, and value.
>
>regards,
>-glenn
>
>
>Subject: Using Option 43 Info FROM a Cable Modem Client to Define a
>Class
>Date: Fri, 12 Oct 2007 13:05:01 -0400
>From: "Perry, Keith" <Keith.Perry at sciatl.com
>
>I have digital settop boxes with embedded cable modems which I'm trying
>to differentiate from plain old stand alone cable modems so I can
>provide different cable modem configuration files to each. Both use
>the same Vendor Class Identifier (Option 60) so that is not an option.
>The embedded cable modem DHCP Discover includes a device type "ECM" in
>sub option 2 of option 43 which I should be able to use. I already use
>Option 60 to create CPE classes so I'm familiar with the syntax for it.
>Below is one of the class definitions I'm defining with Option 60:
>
>
>class "DSG-DHCT" {
> match if option vendor-class-identifier = "DSG1.0";
>}
>
>This looks at the entire Option 60 string. The embedded cable modem
>places 128 bytes of info into Option 43 using 9 seperate sub options as
>shown below:
>
>*********************************************************************
>Option: (t=43,l=128) Vendor-Specific Information (CableLabs)
> Option: (43) Vendor-Specific Information
> Length: 128
> Value: 020345434D030845434D3A4553544204095341424A4E425A...
> Suboption 2: Device Type = "ECM"
> Suboption 3: eSAFE Types = "ECM:ESTB"
> Suboption 4: Serial Number = "SABJNBZTR"
> Suboption 5: Hardware Version = "HW_REV: 1.2; "
> Suboption 6: Software Version = "SW_REV: 2.23.15 build 1
>Release"
> Suboption 7: Boot ROM version = "ROM:049d0106"
> Suboption 8: OUI = "000F21"
> Suboption 9: Model Number = "8300"
> Suboption 10: Vendor Name = "Scientific-Atlanta, Inc."
>
>0140 2e 30 2b 80 02 03 45 43 4d 03 08 45 43 4d 3a 45 .0+...ECM..ECM:E
>0150 53 54 42 04 09 53 41 42 4a 4e 42 5a 54 52 05 0d STB..SABJNBZTR..
>0160 48 57 5f 52 45 56 3a 20 31 2e 32 3b 20 06 1f 53 HW_REV: 1.2; ..S
>0170 57 5f 52 45 56 3a 20 32 2e 32 33 2e 31 35 20 62 W_REV: 2.23.15 b
>0180 75 69 6c 64 20 31 20 52 65 6c 65 61 73 65 07 0c uild 1 Release..
>0190 52 4f 4d 3a 30 34 39 64 30 31 30 36 08 06 30 30 ROM:049d0106..00
>01a0 30 46 32 31 09 04 38 33 30 30 0a 18 53 63 69 65 0F21..8300..Scie
>01b0 6e 74 69 66 69 63 2d 41 74 6c 61 6e 74 61 2c 20 ntific-Atlanta,
>01c0 49 6e 63 2e ff 00 00 00 00 00 00 00 00 00 00 00 Inc.............
>*********************************************************************
>I'm only interested in the sub option 2:
>
>HEX: 2b 80 02 03 [45 43 4d]
>DEC: Option 43| Length 128 | SubOption 2 | Length 3 | [ECM]
>
>I'm not sure how isolate on this sub option. Would something like this
>work?
>
>class "eCM" {
> match if substring (vendor-encapsulated-options, 3, 3) = "ECM"; }
>
>Or should I include the 43 header in the offset?
>
>class "eCM" {
> match if substring (vendor-encapsulated-options, 5, 3) = "ECM"; }
>
>
>I'm open to sugestions. I running Version 3.1 on Solaris, have read
>the Man Pages and have a copy of the Teds "DHCP Handbook".
>
>
>Regards,
>
>Keith Perry
>Sr. Staff Systems Engineer
>WAN/LAN Integration R&D
>Scientific Atlanta
>770-236-3957 (Office)
>770-236-1098 (Lab)
>
>
>
>
>
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