Difference between revisions of "NIDS"

Revision as of 07:07, 29 November 2011

Network layer Intrusion Detection Systems

NIDS are an IDS that monitor all traffic to and from all network devices. It will read incoming packets looking for suspicious patterns. Popular NIDs such as snort and Cisco IDS are used often-times in conjunction with a firewall to form an IPS. Also commonly used to send information to a SIM or SIMS

Snort

Snort is a packet sniffer and intrusion detection system that can be used to add a layer of surveillance to your system. In this way, it is similar to tcpdump, but with some more advanced rule-setting capabilities for detecting certain forms of packets. Snort is one of the most widely used IDSes under Linux, and a port exists for the Windows Operating System.

Basic Packet Sniffing Utilities

Once installed, snort can be set up with basic packet sniffing functionality simply by typing "snort" into a terminal or command prompt. It will run in the default mode using the default interface - for me, this is eth0, the wired connection. A new interface can be specified with the -i option. For example, to run snort on the wireless interace:

By default, the packets will be displayed to STDOUT as packets are capture, which isn't particularly useful. In order to log to a tcpdump-syntax file, you can use the -l option, for example:

In order to read the logs, use a program capable of reading tcpdump-style logs - with tcpdump, use the -r option to read - you may wish to pipe it through less for readability:

Some other useful options:

• -v: show only packet headers
• -vd: show bothc packet headers and data

Rules

Under its default configuration, Snort really isn't much more useful than a packet sniffer - its power as an intrusion detection system comes from its power to process received packets and raise a flag based on a file containing directives on how to treat malformed & potentially malicious packets, which is known as a rule file.

Enable processing a rule file in snort with the -c option, which takes the path to a rule file as its argument.

Rule Layout

A snort rule is composed of two parts: the rule header and the rule options. The rule header contains the action of the rule, its protocol, source and destination IP addresses and netmasks, and information regarding the source and target ports. The option section contains the details of the alert messages and information concerning which parts of the packet should be examined.^[1]