Users Guide

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 Networking OS
is compatible with SSH versions 1.5 and 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 Networking OS Command Line Interface Reference Guide.
Dell 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 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 {1 | 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
Specifying an SSH Version
The following example uses the ip ssh server version 2 command to enable SSH version 2 and the show ip ssh command to
conrm the setting.
Dell(conf)#ip ssh server version 2
Dell(conf)#do show ip ssh
SSH server : enabled.
SSH server version : v2.
SSH server vrf : default.
SSH server ciphers : 3des-cbc,aes128-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-
ctr,aes256-ctr.
SSH server macs : hmac-md5,hmac-md5-96,hmac-sha1,hmac-sha1-96,hmac-sha2-256,hmac-
sha2-256-96.
SSH server kex algorithms : diffie-hellman-group-exchange-sha1,diffie-hellman-group1-
sha1,diffie-hellman-group14-sha1.
Password Authentication : enabled.
Hostbased Authentication : disabled.
RSA Authentication : disabled.
Vty Encryption HMAC Remote IP
Dell(conf)#
784
Security