Cisco Systems 3560X, 3750-X, WSC3750X48TS Configuring Kerberos

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide

OL-21521-01

Chapter 10 Configuring Switch-Based Authentication

Controlling Switch Access with Kerberos

This section describes the first layer of security through which a remote user must pass. The user must

first authenticate to the boundary switch. This process then occurs:

1. The user opens an un-Kerberized Telnet connection to the boundary switch.

2. The switch prompts the user for a username and password.

3. The switch requests a TGT from the KDC for this user.

4. The KDC sends an encrypted TGT that includes the user identity to the switch.

5. 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 either by re-entering the username

and password (noting if Caps Lock or Num Lock is on or off) or by entering a different username

and password.

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.

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, see the “Obtaining a TGT from a KDC” section in

the “Security Server Protocols” chapter of the Cisco IOS Security Configuration Guide, Release 12.2, at

this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter0918

6a00800ca7ad.html#1000999

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, see the “Authenticating to Network

Services” section in the “Security Server Protocols” chapter of the Cisco IOS Security Configuration

Guide, Release 12.2, at this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter0918

6a00800ca7ad.html#1001010

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.