63 lines
2.8 KiB
Plaintext
63 lines
2.8 KiB
Plaintext
@node Things in search for a better place, Kerberos 4 issues, Setting up a realm, Top
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@chapter Things in search for a better place
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@section Making things work on Ciscos
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Modern versions of Cisco IOS has some support for authenticating via
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Kerberos 5. This can be used both to verify passwords via a ticket
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exchange Kerberos 5 (boring), and to use Kerberos authenticated telnet
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to access your router (less boring). The following has been tested on
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IOS 11.2(12), things might be different with other versions. Old
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versions are known to have bugs.
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To make this work, you will first have to configure your router to use
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Kerberos (this is explained in the documentation). A sample
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configuration looks like the following:
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@example
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aaa new-model
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aaa authentication login default krb5-telnet krb5 enable
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aaa authorization exec krb5-instance
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kerberos local-realm FOO.SE
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kerberos srvtab entry host/router.foo.se 0 891725446 4 1 8 012345678901234567
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kerberos server FOO.SE 10.0.0.1
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kerberos instance map admin 15
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@end example
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This tells you (among other things) that the when logging in, the router
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should try to authenticate with kerberized telnet, and if that fails try
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to verify a plain text password via a Kerberos ticket exchange (as
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opposed to a local database or RADIUS or something similar), and if that
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fails try the local enable password. If you're not careful when you
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specify the `login default' authentication mechanism, you might not be
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able to login. The `instance map' and `authorization exec' lines says
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that people with `admin' instances should be given `enabled' shells when
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logging in.
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To make the Heimdal KDC produce tickets that the Cisco can decode you
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might have to turn on the @samp{encode_as_rep_as_tgs_rep} flag in the
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KDC. You will also have to specify that the router can't handle anything
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but @samp{des-cbc-crc}. There currently isn't an easy way to do
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this. The best you can do is to dump your database (with @samp{kadmin -l
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dump}), remove all entries for keys other than @samp{des-cbc-crc}, and
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then reloading the database (@samp{kadmin -l load}). An example should
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clarify this. You should have something like (again, truncated):
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@example
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host/router.foo.se@@FOO.SE 4:0:1:...:-:... - - - - - - - 126
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@end example
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Change this to:
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@example
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host/router.foo.se@@FOO.SE 4:0:1:...:- - - - - - - - 126
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@end example
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This all fine and so, but unless you have an IOS version with encryption
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(available only in the U.S) it doesn't really solve any problems. Sure
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you don't have to send your password over the wire, but since the telnet
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connection isn't protected it's still possible for someone to steal your
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session. This won't be fixed until someone adds integrity to the telnet
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protocol.
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A working solution would be to hook up a machine with a real operating
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system to the console of the Cisco and then use it as a backwards
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terminal server.
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