( Things in search for a better place

Info Catalog ( Applications ( Top ( Kerberos 4 issues
 6 Things in search for a better place
 6.1 Making things work on Ciscos
 Modern versions of Cisco IOS has some support for authenticating via
 Kerberos 5. This can be used both by having the router get a ticket when
 you login (boring), and by using Kerberos authenticated telnet to access
 your router (less boring). The following has been tested on IOS
 11.2(12), things might be different with other versions. Old versions
 are known to have bugs.
 To make this work, you will first have to configure your router to use
 Kerberos (this is explained in the documentation). A sample
 configuration looks like the following:
      aaa new-model
      aaa authentication login default krb5-telnet krb5 enable
      aaa authorization exec krb5-instance
      kerberos local-realm FOO.SE
      kerberos srvtab entry host/ 0 891725446 4 1 8 012345678901234567
      kerberos server FOO.SE
      kerberos instance map admin 15
 This tells you (among other things) that when logging in, the router
 should try to authenticate with kerberised telnet, and if that fails try
 to verify a plain text password via a Kerberos ticket exchange (as
 opposed to a local database, RADIUS or something similar), and if that
 fails try the local enable password. If you're not careful when you
 specify the `login default' authentication mechanism, you might not be
 able to login at all. The `instance map' and `authorization exec' lines
 says that people with `admin' instances should be given `enabled' shells
 when logging in.
 The numbers after the principal on the `srvtab' line are principal type,
 time stamp (in seconds since 1970), key version number (4), keytype (1
 == des), key length (always 8 with des), and then the key.
 To make the Heimdal KDC produce tickets that the Cisco can decode you
 might have to turn on the `encode_as_rep_as_tgs_rep' flag in the KDC.
 You will also have to specify that the router can't handle anything but
 `des-cbc-crc'. This can be done with the `del_enctype' command of
 This all fine and so, but unless you have an IOS version with encryption
 (available only in the U.S) it doesn't really solve any problems. Sure
 you don't have to send your password over the wire, but since the telnet
 connection isn't protected it's still possible for someone to steal your
 session. This won't be fixed until someone adds integrity to the telnet
 A working solution would be to hook up a machine with a real operating
 system to the console of the Cisco and then use it as a backwards
 terminal server.
Info Catalog ( Applications ( Top ( Kerberos 4 issues
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