Dell S4820T, Configuration Manual

Page: 875 / 1178

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 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 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 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 confirm 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-
Security
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