FW: [ISC-Bugs #37715] AutoReply: dhcp-4.3.1 and initial versions. - dhcp user class option 77 encoding is not encoding as per the RFC.

[Glenn Satchell]

Seems dhclient is not the only one getting this wrong:

https://ask.wireshark.org/questions/35332/dhcp-option-77-malformed-option

Microsoft doesn't seem to think it needs the sub item lengths:

http://technet.microsoft.com/en-us/library/dd145324%28v=ws.10%29.aspx

iPXE also uses it in the same way:

http://forum.ipxe.org/showthread.php?tid=7530

So maybe, the defacto use case is to non-compliant and treat the option as
a single string, rather than the array of strings?

regards,
-glenn

On Wed, November 26, 2014 3:21 am, Venkatesh Siddappa wrote:
> Hi,
>
> Please let me know if anyone faced following issue.
>
> Thanks,
> Venkatesh.
>
>
> -----Original Message-----
> From: DHCP Bugs via RT [mailto:dhcp-bugs at isc.org]
> Sent: Tuesday, November 04, 2014 7:00 PM
> To: Venkatesh Siddappa
> Subject: [ISC-Bugs #37715] AutoReply: dhcp-4.3.1 and initial versions. -
> dhcp user class option 77 encoding is not encoding as per the RFC.
>
>
> Greetings,
>
> This message has been automatically generated in response to the creation
> of a trouble ticket regarding:
> 	"dhcp-4.3.1 and initial versions. - dhcp user  class  option 77 encoding
> is not encoding as per the RFC.", a summary of which appears below.
>
> There is no need to reply to this message right now.  Your ticket has been
> assigned an ID of [ISC-Bugs #37715].
>
> Please include the string:
>
>          [ISC-Bugs #37715]
>
> in the subject line of all future correspondence about this issue. To do
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>                         Thank you,
>                         dhcp-bugs at isc.org
>
> -------------------------------------------------------------------------
> Bug Report from www.isc.org:
>
>   * Name: venkatesh
>
>   * Email: venkatesh.siddappa at oneaccess-net.com
>
>   * Software Version: dhcp-4.3.1 and initial versions.
>
>   * OS: Linux
>
>   * Subject:dhcp user class option 77 encoding is not encoding as per the
> RFC.
>
> Bug Detail
>
> The format of this option is as follows:
>
> Code Len Value
> +—–+—–+——————— . . . –+
> | 77 | N | User Class Data ('Len' octets) |
> +—–+—–+——————— . . . –+
>
> UC_Len_i User_Class_Data_i
> +——–+———————— . . . –+
> | L_i | Opaque-Data ('UC_Len_i' octets) |
> +——–+———————— . . . –+
>
> Each User Class value (User_Class_Data_i) is indicated as an opaque field.
> The value in UC_Len_i does not include the length field itself and MUST be
> non-zero. Let m be the number of User Classes carried in the option. The
> length of the option as specified in Len must be the sum of the lengths of
> each of the class names plus m:
> Len= UC_Len_1 + UC_Len_2 + … + UC_Len_m + m. If any instances of User
> Class Data are present, the minimum value of Len is two (Len =
> UC_Len_1 + 1 = 1 + 1 = 2)
>
> ===
> config:
>
> debian73-32bit:/home/oauser/opensource/dhcp-4.3.1/client# cat
> /etc/dhcp/dhclient.conf # Configuration file for /sbin/dhclient, which is
> included in Debian's # dhcp3-client package.
> #
> # This is a sample configuration file for dhclient. See dhclient.conf's #
> man page for more information about the syntax of this file # and a more
> comprehensive list of the parameters understood by # dhclient.
> #
> # Normally, if the DHCP server provides reasonable information and does #
> not leave anything out (like the domain name, for example), then # few
> changes must be made to this file, if any.
> #
>
> option rfc3442-classless-static-routes code 121 = array of unsigned
> integer 8;
>
> #send host-name "andare.fugue.com";
> #send host-name = gethostname();
> #send dhcp-client-identifier 1:0:a0:24:ab:fb:9c; #send
> dhcp-client-identifier eth0; #send dhcp-lease-time 3600; #send
> dhcp-lease-time 36; send user-class "MC76"; #send vendor-class-identifier
> "1:0:a0:24:ab:fb:9c"; #supersede domain-name "fugue.com home.vix.com";
> #prepend domain-name-servers 127.0.0.1; #omapi port 7911; request
> subnet-mask, broadcast-address, time-offset, routers, domain-name,
> domain-name-servers, domain-search, host-name, dhcp6.name-servers,
> dhcp6.domain-search, netbios-name-servers, netbios-scope, interface-mtu,
> rfc3442-classless-static-routes, ntp-servers, static-routes,
> extensions-path; #require subnet-mask, domain-name-servers; #timeout 60;
> #retry 60; #reboot 10; #select-timeout 5; #initial-interval 2; #script
> "/etc/dhcp3/dhclient-script"; #media "-link0 -link1 -link2", "link0
> link1"; #reject 192.33.137.209;
>
> #alias {
> # interface "eth0";
> # fixed-address 192.5.5.213;
> # option subnet-mask 255.255.255.255;
> #}
>
> #lease {
> # interface "eth0";
> # fixed-address 192.33.137.200;
> # medium "link0 link1";
> # option host-name "andare.swiftmedia.com"; # option subnet-mask
> 255.255.255.0; # option broadcast-address 192.33.137.255; # option routers
> 192.33.137.250; # option domain-name-servers 127.0.0.1; # renew 2
> 2000/1/12 00:00:01; # rebind 2 2000/1/12 00:00:01;
> =============================== comand executed:
> debian73-32bit:/home/oauser/opensource/dhcp-4.3.1/client# ./dhclient -4 -d
> -cf /etc/dhcp/dhclient.conf eth1
>
> ====
>
> If i see in the wireshark "user-class "MC76";", is encoding as -> 4d 04 4d
> 43
> 37 36
> But ideally it should have been in the form -> 4d 05 04 4d 43 37 36
>
> DHCP servers not able to give offers because of user-class not matched.
>
> Please let me know whether "user class option " not handled in isc dhcp
> cleint.
>
> Thanks,
> venkatesh.
>
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