User`s guide

ZyWALL IDP 10 User’s Guide
Appendix A Introduction to Intrusions 108
Appendix A
Introduction to Intrusions
Introduction to Ports
Computers share information over the Internet using a common language called TCP/IP. An
“extension number”, called the "TCP port" or "UDP port" identifies these protocols, such as
HTTP (Web), FTP (File Transfer Protocol), POP3 (e-mail), etc. For example, Web traffic by
default uses TCP port 80.
When computers communicate on the Internet, they are using a client/server model, where the
server "listens" on a specific TCP/UDP port for information requests from remote client
computers on the network.
Some of the most common IP ports are:
Table 32 Common IP Ports
Introduction to Denial of Service
The goal of Denial of Service (DoS) attacks is not to steal information, but to disable a device
or network on the Internet.
The following are some DoS example attacks.
Buffer Overflow Attacks
A buffer overflow occurs when a program or process tries to store more data in a buffer
(temporary data storage area) than it was intended to hold. The excess information can
overflow into adjacent buffers, corrupting or overwriting the valid data held in them.
Intruders could run codes in the overflow buffer region to obtain control of the system, install
a backdoor or use the victim to launch attacks on other devices.
21 FTP 53 DNS
23 Telnet 80 HTTP
25 SMTP 110 POP3