Bug #48604 for dhcp-public: The dhclient.conf - user-option not documented clearly

Dear Sir/Madam, I finally got to the core of the problems with dhclient.conf, documentation etc. Everything was cause by the 'send user-class "some-user-class"' entry in the dhclient.conf file. It appears that according to the RFC 3004 one needs to have the user-class string entered as "\017some-user-class". It would well support and m-array of user classes in this option. It would be neat though to have that documented. Without the length-meaning non-printable characters I was experiencing the 'malformed' packets emitted by the client. The dhclient version in use 4.4.1. With my best wishes Tomasz Motyl -----Original Message----- From: DHCP Public Bugs via RT [mailto:dhcp-public@isc.org] Sent: 07 December 2018 00:36 To: Tomasz Motyl <tomasz.motyl@se.com> Subject: [ISC-Bugs #48604] AutoReply: The dhclient.conf problems... 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The documentation is extremely vague in that area and I believe that number of examples (man pages provide us with only one) would be of extreme benefit. Actually trivial thing from the perspective of the protocol - option 60 to be sent by the client in the DHCP request packet. I strongly encourage you to try googling it... I daresay would be faster writing the packet in the hex editor and push it raw to the wire than figure out how to do this reading the man-pages. Yes this is that bad. With my best wishes Tomasz Motyl ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________

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Hello Tomasz: Thank for you bringing this matter to our attention. After reviewing the issue you are certainly correct in that our documentation is sorely lacking regarding the user-class option. ISC DHCP server and client treat the option as straight text and that does seem to defy RFC 3004. However the implementation has been in place for a very long time and changing it now would likely upset more apple carts than it would right. As you've already discovered one must encode the length into the string value to produce a compliant result. In fact, you can use that technique to encode an option with multiple values: send user-class "\007myclass\013another-one"; Thus it is possible to send multiple length-value tuples as described in RFC 3004. I apologize for the inconvenience the lack of documentation caused you. We will be clarifying this in our documentation as part of our next maintenance releases, 4.4.2 and 4.1-ESV-R16 (dates are TBD). We like to thank our contributors by citing them in the release notes. If you would like to be thanked in this manner, please reply with how you would like to be identified. Typically it is by name and/or organization. Thanks for taking the time and interest to report this issue to us. Regards, Thomas Markwalder ISC Software Engineering

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