Concept Guide

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Command Authorization
The AAA command authorization feature congures Dell EMC Networking OS to send each conguration command to a TACACS server
for authorization before it is added to the running conguration.
By default, the AAA authorization commands congure 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 cong, and a message displays:
04:07:48: %RPM0-P:CP %SEC-3-SEC_AUTHORIZATION_FAIL: Authorization failure Command
authorization 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 local
tacacs+ command. To resolve the issue, use the aaa authorization commands level default tacacs+ local
command.
Protection from TCP Tiny and Overlapping Fragment
Attacks
Tiny and overlapping fragment attack is a class of attack where congured ACL entries — denying TCP port-specic trac — is bypassed
and trac is sent to its destination although denied by the ACL.
RFC 1858 and 3128 proposes a countermeasure to the problem. This countermeasure is congured into the line cards and enabled by
default.
Enabling SCP and SSH
Secure shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. Dell EMC Networking
OS is compatible with SSH versions 2, in both the client and server modes. SSH sessions are encrypted and use authentication. SSH is
enabled by default.
For details about the command syntax, refer to the Security chapter in the Dell EMC Networking OS Command Line Interface Reference
Guide.
Dell EMC Networking OS SCP, which is a remote le 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 EMC
Networking OS-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 SSH
client.
EXEC Privilege mode
ssh {hostname} [-l username | -p port-number | -v 2}| -c encryption cipher | -m HMAC algorithm
hostname 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 mode
show ip ssh
768
Security