TCP/IP Tutorial and Technical Overview - IBM Redbooks

Where:
RSV Reserved for future use. All bytes are zero.
FRAG Current fragment number.
ATYP Address types in octets:
X'01' IPv4 address
X'03' Domain-name
X'04' IPv6 address
DST.ADDR Desired destination address.
DST.PORT Desired destination port in network octet order.
DATA User data.
The UDP relay server gets the IP address of the client, which sends UDP
datagrams to the port specified by DST.PORT. It then discards any datagram
that comes from another source.
22.6 Secure Shell (1 and 2)
22.6.1 SSH overview
SSH can secure connections between systems. It allows application traffic, such
as that generated by Telnet, FTP POP3, or even X Window System, to be both
encrypted and compressed. Compression is useful over slow modem links.
Implementations allow the user a choice of encryption methods.
Client software often offers both SSH1 and SSH2 support. The user is
authenticated by password or public/private key.
SSH1 offers Blowfish, DES, 3DES, and RC4 encryption ciphers.
SSH2 offers 3DES, RC4, and Twofish encryption ciphers.
SSH establishes a single TCP/IP connection from the client to the server. The
traffic sent down this connection is encrypted, and optionally compressed using
LempleZiv compression. Public/private keys can be used to verify both the user
and the identity of the remote system.
SSH and X Window System
X Window System sessions can pass through the SSH connection. The SSH
server generates a new DISPLAY variable (and xauth key) for the remote
Chapter 22. TCP/IP security 853