2 @c $NetBSD: kerberos4.texi,v 1.1.1.3 2014/04/24 12:45:26 pettai Exp $
4 @node Kerberos 4 issues, Windows compatibility, Things in search for a better place, Top
5 @comment node-name, next, previous, up
6 @chapter Kerberos 4 issues
8 Kerberos 4 KDC and KA server have been moved.
10 For more about AFS, see the section @xref{AFS}.
13 * Principal conversion issues::
14 * Converting a version 4 database::
17 @node Principal conversion issues, Converting a version 4 database, Kerberos 4 issues, Kerberos 4 issues
18 @section Principal conversion issues
20 First, Kerberos 4 and Kerberos 5 principals are different. A version 4
21 principal consists of a name, an instance, and a realm. A version 5
22 principal has one or more components, and a realm (the terms ``name''
23 and ``instance'' are still used, for the first and second component,
24 respectively). Also, in some cases the name of a version 4 principal
25 differs from the first component of the corresponding version 5
26 principal. One notable example is the ``host'' type principals, where
27 the version 4 name is @samp{rcmd} (for ``remote command''), and the
28 version 5 name is @samp{host}. For the class of principals that has a
29 hostname as instance, there is an other major difference, Kerberos 4
30 uses only the first component of the hostname, whereas Kerberos 5 uses
31 the fully qualified hostname.
33 Because of this it can be hard or impossible to correctly convert a
34 version 4 principal to a version 5 principal @footnote{the other way is
35 not always trivial either, but usually easier}. The biggest problem is
36 to know if the conversion resulted in a valid principal. To give an
37 example, suppose you want to convert the principal @samp{rcmd.foo}.
39 The @samp{rcmd} name suggests that the instance is a hostname (even if
40 there are exceptions to this rule). To correctly convert the instance
41 @samp{foo} to a hostname, you have to know which host it is referring
42 to. You can to this by either guessing (from the realm) which domain
43 name to append, or you have to have a list of possible hostnames. In the
44 simplest cases you can cover most principals with the first rule. If you
45 have several domains sharing a single realm this will not usually
46 work. If the exceptions are few you can probably come by with a lookup
47 table for the exceptions.
49 In a complex scenario you will need some kind of host lookup mechanism.
50 Using DNS for this is tempting, but DNS is error prone, slow and unsafe
51 @footnote{at least until secure DNS is commonly available}.
53 Fortunately, the KDC has a trump on hand: it can easily tell if a
54 principal exists in the database. The KDC will use
55 @code{krb5_425_conv_principal_ext} to convert principals when handling
56 to version 4 requests.
58 @node Converting a version 4 database, , Principal conversion issues, Kerberos 4 issues
59 @section Converting a version 4 database
61 If you want to convert an existing version 4 database, the principal
62 conversion issue arises too.
64 If you decide to convert your database once and for all, you will only
65 have to do this conversion once. It is also possible to run a version 5
66 KDC as a slave to a version 4 KDC. In this case this conversion will
67 happen every time the database is propagated. When doing this
68 conversion, there are a few things to look out for. If you have stale
69 entries in the database, these entries will not be converted. This might
70 be because these principals are not used anymore, or it might be just
71 because the principal couldn't be converted.
73 You might also see problems with a many-to-one mapping of
74 principals. For instance, if you are using DNS lookups and you have two
75 principals @samp{rcmd.foo} and @samp{rcmd.bar}, where `foo' is a CNAME
76 for `bar', the resulting principals will be the same. Since the
77 conversion function can't tell which is correct, these conflicts will
78 have to be resolved manually.
80 @subsection Conversion example
82 Given the following set of hosts and services:
90 you have a database that consists of the following principals:
92 @samp{rcmd.foo}, @samp{rcmd.mail}, @samp{pop.mail}, @samp{rcmd.ftp}, and
95 lets say you also got these extra principals: @samp{rcmd.gone},
96 @samp{rcmd.old-mail}, where @samp{gone.foo.se} was a machine that has
97 now passed away, and @samp{old-mail.foo.se} was an old mail machine that
98 is now a CNAME for @samp{mail.foo.se}.
100 When you convert this database you want the following conversions to be
104 rcmd.mail host/mail.foo.se
105 pop.mail pop/mail.foo.se
106 rcmd.ftp host/ftp.bar.se
107 ftp.ftp ftp/ftp.bar.se
108 rcmd.gone @i{removed}
109 rcmd.old-mail @i{removed}
112 A @file{krb5.conf} that does this looks like:
124 v4_instance_convert = @{
128 default_domain = foo.se
132 The @samp{v4_name_convert} section says which names should be considered
133 having an instance consisting of a hostname, and it also says how the
134 names should be converted (for instance @samp{rcmd} should be converted
135 to @samp{host}). The @samp{v4_instance_convert} section says how a
136 hostname should be qualified (this is just a hosts-file in
137 disguise). Host-instances that aren't covered by
138 @samp{v4_instance_convert} are qualified by appending the contents of
139 the @samp{default_domain}.
141 Actually, this example doesn't work. Or rather, it works to well. Since
142 it has no way of knowing which hostnames are valid and which are not, it
143 will happily convert @samp{rcmd.gone} to @samp{host/gone.foo.se}. This
144 isn't a big problem, but if you have run your kerberos realm for a few
145 years, chances are big that you have quite a few `junk' principals.
147 If you don't want this you can remove the @samp{default_domain}
148 statement, but then you will have to add entries for @emph{all} your hosts
149 in the @samp{v4_instance_convert} section.
151 Instead of doing this you can use DNS to convert instances. This is not
152 a solution without problems, but it is probably easier than adding lots
153 of static host entries.
155 To enable DNS lookup you should turn on @samp{v4_instance_resolve} in
156 the @samp{[libdefaults]} section.
158 @subsection Converting a database
160 The database conversion is done with @samp{hprop}. You can run this
161 command to propagate the database to the machine called
162 @samp{slave-server} (which should be running a @samp{hpropd}).
165 hprop --source=krb4-db --master-key=/.m slave-server
168 This command can also be to use for converting the v4 database on the
172 hprop -n --source=krb4-db -d /var/kerberos/principal --master-key=/.m | hpropd -n