Deployment Guide

Protection from TCP Tiny and Overlapping Fragment
Attacks
Tiny and overlapping fragment attack is a class of attack where configured ACL entries — denying TCP port-specific traffic —
is bypassed and 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 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 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 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
The following example uses the ip ssh server version 2 command to enable SSH version 2 and the show ip ssh
command to confirm the setting.
DellEMC(conf)#ip ssh server version 2
DellEMC(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
DellEMC(conf)#
To disable SSH server functions, use the no ip ssh server enable command.
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Security