Authenticating To A Boundary Switch - Cisco Catalyst 3550 series Software Configuration Manual

Chapter 8 Configuring Switch-Based Authentication

Authenticating to a Boundary Switch

This section describes the first layer of security through which a remote user must pass. The user must
first authenticate to the boundary switch. When the remote user authenticates to a boundary switch, this
process occurs:
1.
2.
3.
4.
5.
A remote user who initiates a un-Kerberized Telnet session and authenticates to a boundary switch is
inside the firewall, but the user must still authenticate directly to the KDC before getting access to the
network services. The user must authenticate to the KDC because the TGT that the KDC issues is stored
on the switch and cannot be used for additional authentication until the user logs on to the switch.
Obtaining a TGT from a KDC
This section describes the second layer of security through which a remote user must pass. The user must
now authenticate to a KDC and obtain a TGT from the KDC to access network services.
For instructions about how to authenticate to a KDC, refer to the "Obtaining a TGT from a KDC" section
in the "Security Server Protocols" chapter of the Cisco IOS Security Configuration Guide, Release 12.1,
at this URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/secur_c/scprt2/
scdkerb.htm#xtocid154005.
Authenticating to Network Services
This section describes the third layer of security through which a remote user must pass. The user with
a TGT must now authenticate to the network services in a Kerberos realm.
For instructions about how to authenticate to a network service, refer to the "Authenticating to Network
Services" section in the "Security Server Protocols" chapter of the Cisco IOS Security Configuration
Guide, Release 12.1,at this URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/secur_c/scprt2/
scdkerb.htm#xtocid154006.
Configuring Kerberos
So that remote users can authenticate to network services, you must configure the hosts and the KDC in
the Kerberos realm to communicate and mutually authenticate users and network services. To do this,
you must identify them to each other. You add entries for the hosts to the Kerberos database on the KDC
and add KEYTAB files generated by the KDC to all hosts in the Kerberos realm. You also create entries
for the users in the KDC database.
78-11194-09
The user opens an un-Kerberized Telnet connection to the boundary switch.
The switch prompts the user for a username and password.
The switch requests a TGT from the KDC for this user.
The KDC sends an encrypted TGT to the switch that includes the user identity.
The switch attempts to decrypt the TGT by using the password that the user entered.
• If the decryption is successful, the user is authenticated to the switch.
• If the decryption is not successful, the user repeats Step 2 by re-entering the username and
password (noting if Caps Lock or Num Lock is on or off) or by entering a different usernname
and password.
Controlling Switch Access with Kerberos
Catalyst 3550 Multilayer Switch Software Configuration Guide
8-35