[secdir] secdir review of draft-sakane-dhc-dhcpv6-kdc-option

Samuel Weiler <weiler+secdir@watson.org> Wed, 23 May 2012 23:12 UTC

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Date: Wed, 23 May 2012 19:12:17 -0400
From: Samuel Weiler <weiler+secdir@watson.org>
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Subject: [secdir] secdir review of draft-sakane-dhc-dhcpv6-kdc-option
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I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG.  These comments were written primarily for the benefit of the
security area directors.  Document editors and WG chairs should treat
these comments just like any other last call comments.

This doc specifies several DHCPv6 options for carrying Kerberos config 
info.  There are obvious risks to doing this, but they're discussed 
reasonably well in this and similar cited docs (e.g. RFC3634, which 
specifies a much more limited option for DHCPv4).  The doc explains by 
DNS service discovery isn't ideal for some environments.

With that said, there are some things that need clarification, and the 
doc sorely needs an editorial pass.  As-is, the doc is not ready for 
publication.  I will be happy to review the doc again once it's been 
thoroughly edited.

Things that need clarification or consideration:

For the transport type field, would it be better to use a bitmask? 
Then one could use a single DHCPv6 option to specify a KDC that's 
reachable over both TCP and UDP, rather than needing two DHCPv6 

Section 7 uses the term "TGT" without expansion.  In the Kerberos 
world I can't imagine someone not knowing what this is, but it's not 
clear to the layman.  It probably needs to be expanded.

The algorithm in section 4.1 needs work.  The obvious thing is to read 
it linearly.  Doing that, one would prefer DHCP over DNS SVR info (per 
step 2), which is not what step 6 and the graphic say.

Saying "no answer from the DNS server" is probably not the desired 

In 3.4, the option-len field is ambiguous.  It says "24-octet + the 
length of the realm-name field in octets."  But it looks to me like 
this option is 27 octets + length of realm name.  Perhaps it would be 
better to just count the length of the realm name?

And here are some examples of wording that needs work.  There are many 
more -- I quit copying them into this review after the first few:

3.2 "This option informs a DHCPv6 server of which realm the client 
want to access, ..."

7 "... a rogue KDC that does not know the client access."  What is 
"the client access"?

"The incorrect KDC is not be able to proceed any further state of the 

"The considerable situation is that the support of an unconfigured 
workstation used by multiple users, which obtains its KDC information 
and default realm via DHCP."