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1.6.3 Configuring Kerberos

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Information

Kerberos is a secret-key network authentication protocol, developed at the Massachusetts Institute of Technology (MIT), that uses the Data Encryption Standard (DES) cryptographic algorithm for encryption and authentication. Kerberos was designed to authenticate requests for network resources. Kerberos, like other secret-key systems, is based on the concept of a trusted third party that performs secure verification of users and services. In the Kerberos protocol, this trusted third party is called the key distribution center (KDC).

The primary use of Kerberos is to verify that users and the network services they use are really who and what they claim to be. To accomplish this, a trusted Kerberos server issues tickets to users. These tickets, which have a limited lifespan, are stored in a user's credential cache and can be used in place of the standard username-and-password authentication mechanism.

The Kerberos credential scheme embodies a concept called 'single logon.' This process requires authenticating a user once, and then allows secure authentication (without encrypting another password) wherever that user's credential is accepted.

Cisco IOS XE software includes Kerberos 5 support, which allows organizations already deploying Kerberos 5 to use the same Kerberos authentication database on their routers that they are already using on their other network hosts (such as UNIX servers and PCs).

The following network services are supported by the Kerberos authentication capabilities in Cisco IOS XE software:

Telnet

rlogin

rsh

rcp

Rationale:

Authenticating to the Boundary Router This section describes the first layer of security that remote users must pass through when they attempt to access a network. The first step in the Kerberos authentication process is for users to authenticate themselves to the boundary router. The following process describes how users authenticate to a boundary router:

Impact:

A remote user who successfully initiates a PPP session and authenticates to the boundary router is inside the firewall but still must authenticate to the KDC directly before being allowed to access network services. This is because the TGT issued by the KDC is stored on the router and is not useful for additional authentication unless the user physically logs on to the router.

Solution

Adding Users to the KDC Database

Hostname# ank {username@REALM}
Hostname# ank {username/instance@REALM

Creating SRVTABs on the KDC

Hostname# ark {SERVICE/HOSTNAME@REALM}

Make entries for all network services on all Kerberized hosts that use this KDC for authentication.
Defining a Kerberos Realm

Hostname#(config)kerberos local-realm {kerberos-realm}
Hostname#(config)kerberos server {kerberos-realm {hostname | ip-address}} {port-number}
Hostname#(config)kerberos realm {dns-domain | host} {kerberos-realm}

Default Value:

no kerberos enabled

See Also

https://workbench.cisecurity.org/files/3801

Item Details

References: CSCv7|5.1

Plugin: Cisco

Control ID: 3e82fe045dd47008512cb02021c0bacc7fa7ed13bfd8d7b0e892298422b54e95