Command AuthorizationThe AAA command authorization feature configures Dell Networking OS to send each configuration command to a TACACS server forauthorization before it is added to the running configuration.By default, the AAA authorization commands configure the system to check both EXEC mode and CONFIGURATION mode commands.Use the no aaa authorization config-commands command to enable only EXEC mode command checking.If rejected by the AAA server, the command is not added to the running config, and a message displays:04:07:48: %RPM0-P:CP %SEC-3-SEC_AUTHORIZATION_FAIL: Authorization failure Commandauthorization failed for user (denyall) on vty0 ( 10.11.9.209 )Certain TACACS+ servers do not authenticate the device if you use the aaa authorization commands level default localtacacs+ command. To resolve the issue, use the aaa authorization commands level default tacacs+ localcommand.Protection from TCP Tiny and Overlapping FragmentAttacksTiny and overlapping fragment attack is a class of attack where configured ACL entries — denying TCP port-specific traffic — is bypassedand traffic is sent to its destination although denied by the ACL.RFC 1858 and 3128 proposes a countermeasure to the problem. This countermeasure is configured into the line cards and enabled bydefault.Enabling SCP and SSHSecure shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. Dell Networking OSis compatible with SSH versions 1.5 and 2, in both the client and server modes. SSH sessions are encrypted and use authentication. SSH isenabled by default.For details about the command syntax, refer to the Security chapter in the Dell Networking OS Command Line Interface Reference Guide.Dell Networking OS SCP, which is a remote file copy program that works with SSH.NOTE: The Windows-based WinSCP client software is not supported for secure copying between a PC and a Dell NetworkingOS-based system. Unix-based SCP client software is supported.To use the SSH client, use the following command.• Open an SSH connection and specify the hostname, username, port number,encryption cipher,HMAC algorithm and version of the SSHclient.EXEC Privilege modessh {hostname} [-l username | -p port-number | -v {1 | 2}| -c encryption cipher | -m HMACalgorithmhostname is the IP address or host name of the remote device. Enter an IPv4 or IPv6 address in dotted decimal format (A.B.C.D).• SSH V2 is enabled by default on all the modes.• Display SSH connection information.EXEC Privilege modeshow ip sshSecurity 811
