1. Ch 3 Firewall and Perimeter Security

2. Contents Firewall NAT IDS Honeypots
packet-filter firewall: filters at the network or transport layer
proxy firewall: filters at the application layer
NAT
solve the problem of IP address limitation
provide load balance and redundancy
IDS
active detection to monitor the network status
three methods: signature, statistical and integrity
four types: host, network, applications and integrity
Honeypots
a décor to attract hackers

3. What is a firewall?
A firewall, is a “router, or several routers or access servers, designed as a buffer between any connected public networks and private network.

4. Protecting Network using Firewall - 1
Security protocol cannot prevent malicious people from sending harmful message to a system
A firewall is a device (usually a router or computer) installed between internal network and the Internet
Some large companies with a lot of sensitive information also install firewall within their intranet to protect these types of the network resource from unauthorized employee.

5. Protecting Network using Firewall - 2
Some modern firewall has additional features:
network address translation (NAT)
encryption in data transmission, e.g. VPN
use strong authentication techniques to authenticate users/ports
anti-virus features
easy to use GUI

6. Requirements of firewall
Efficient access control (easy to use access control list (ACL), such as GUI interface)
Filtering of vulnerable protocols (based on types of protocols)
Network monitoring
Simple management (features such as GUI, web-based, SNMP enabled)

7. Firewall classification
A firewall is usually classified into two classes
packet-filter firewall
also known as screen router or screening filter
forward and block packets based on information in the network layer and transport layer headers: source, destination, IP address, source and destination port, type of protocol (TCP or UDP)
proxy-based firewall
also known as application gateway
forward and block packets based on the contents of the messages (I.e. at application level traffic)

8. Packet-filter firewall - 1
is a router that uses a filtering table to decide which packet must be discard (not forward)
operate at network layer (or transport layer)
A packet filter performs the following functions.
1. Receive each packet as it arrives.
2. Pass the packet through a set of rules, based on the contents of the IP and transport header
fields of the packet. If there is a match with one of the set rules, decide whether to acceptor discard the packet based on that rule. For example, a rule could specify: disallow all
incoming traffic from an IP address (this IP address is taken just as an
example), or disallow all traffic that uses UDP as the higher (transport) layer protocol.
3. If there is no match with any rule, take the default action. The default can be discard
all packets, or accept all packets. The former policy is more conservative, whereas the latter
is more open. Usually, the implementation of a firewall begins with the default discard
all packets option, and then rules are applied one-by-one to enforce packet filtering.

9. Packet-filter firewall - 2
Example of packet filter rules:
incoming packet from are blocked
incoming packet destined for any internal TELNET (port 23) are blocked
incoming packets destined to internal host are blocked (this host for internal use)
outgoing packets destined for an HTTP server (port 80) are blocked. (i.e. does not want employees to browser the Internet)

10. Packet Filtering Firewall - 1
Two main types:
Standard or Stateless packet filtering
Also known as first generation firewall
Operates at either the Network or Transport layer.
Most packet filters used the values of the following header field to determine what to pass or not
Protocol type, IP address, TCP/UDP port, Fragment number

11. Standard packet filtering
Packet filters make decisions based on packet header information.
Access decisions are based on source and destination addresses, source and destination port numbers, protocol types, and possibly flags within the header themselves.
They does not look at the actual payload.

12. Packet Filtering Firewall - 2
Stateful inspection packet filters
known as dynamic packet filtering
filter rules are set up based on policy rule and state of the protocol
For example:
do not allow any services through the firewall except:
Services they’re programmed to allow
Connections that they already maintained in their state tables.

13. Stateful inspection packet filter
Allow incoming TCP packets only if they are responses to the outgoing TCP packets that have gone through our network.

14. Pros and Cons of Packet Filter
Scalable (Simple)
Provides high performance (High speed)
Application dependent
Cons
Does not look into the packet pass the header.
Low security relative to other firewall types
Difficulties in setting up the packet filter rules correctly
Lack of support for authentication

15. Stateful Multilevel Inspection - 1
First implemented by CheckPoint under the name “Stateful Multilevel Inspection”.
Stateful Rules are protocol-specific, keeping track of the context of a session (not just its state).
The greatest addition that stateful multilevel filtering provides to dynamic filtering is the ability to maintain application state, not just connection state.

16. Stateful Multilevel Inspection - 2
This allows filtering rules to differentiate between the various connectionless protocols (like UDP, NFS and RPC), which were previously immune to management by static filtering and were not uniquely identified by dynamic filtering
Application state allows a previously authenticated user to create new connections without reauthorizing, whereas connection state just maintains that authorization for the duration of a single session.

17. Proxy-based firewall Application Level firewall for example
Make high-level connections at application layer
for example
Policy on access web-pages: Only Internet users who had established business relationships with the company can have access; access by other users must be blocked.
packet-filter firewall is not feasible because it cannot distinguish between different packet. Selection must be done at applications level (i.e. URL)
proxy work on behalf of internal hosts to complete the connection between internal and external hosts.

18. Proxy-based firewall (2)
A variants of proxy is called circuit gateway
creates a new connection between itself and the remote host
Proxy stand in for outbound connection attempts to servers and then make the request to the actual target server on behalf of the client. When the server returns data, the proxy transmits that data to the client.
Application proxies don’t necessary to be run on firewalls appliances.
it is a high-end servers (or cluster of servers)
Usually Internet client applications (Browser) require to setup to talk to the proxy.

19. Proxy-based firewall (3)

20. Application gateway creates an illusion

21. Additional Firewall Components
Authentication
Allows users on the public network to prove their identity to the firewall in order to gain access to the private network from external locations.
to filter unauthorized users
function as an NAS (network access server)
Encrypted Tunnels
tunneling is also called encapsulation, it is a major building block of Virtual Private Networking (VPN)
Tunneling establishes a secure connection between two private networks over a public medium like the Internet.
allows physically separated networks to use the Internet rather than leased-line connections to communicate.
VPN firewall is usually work in pairs

22. Limitations of Firewall
Even with the use of Proxy firewalls, it is still unable to control the content transferred across the network boundaries satisfactorily.
Firewalls are extremely vulnerable to insider attacks and covert channels
Firewalls can become bottlenecks of traffic
If a firewall is compromised, the protected network is extremely vulnerable
State any TWO limitations of a firewall in general.
A covert channel enables the prisoners to exchange secret information through messages that appear to be innocuous. A covert channel requires prior agreement on the part of the prisoners.

23. Security Strategies in firewall
Least privilege
every element of the firewalls system should have only the privileges that are needed to carry out its tasks
Defense in depth
security mechanisms should be redundant, should use different approaches (e.g. from different vendors), and should be able to back up each other.
Controlled access
the protected network should have a well-defined access point that forces attackers to use a narrow channel, which you can monitor and control
Fail-safe & fail-over
Fail-safe: a malfunctioning of a subsystem may affect functionality but should not lose security.
Fail-over: the task can taken over by another firewall.

24. Firewall Philosophies
Default Permit:
“Not Expressly Prohibited” is Permitted
Used in “open” environments (e.g., ISP and some universities)
Difficult to manage
Default Deny:
“Not Expressly Permitted” is Prohibited
used in environment with higher security
May be too restrictive in some environments

25. Factors to consider for choosing firewall
Performance
Firewall is usually the bottle neck of network traffics. The performance is usually the prime concerns. Stateful inspection filter is the trend as it’s good cost-performance ratio is better.
Scalability
scale adapted to size of company and corporate security policy. Usually, firewall vendor provide modules for client to upgrade according to their needs
Compatibility
work seamlessly with firewall products from different vendors
Network management support
easy installation and compatible with network management protocol

26. Examples of Firewall Configurations - 1
In practical implementations, a firewall is usually a combination of packet filters and application (or circuit) gateways.

27. Examples of Firewall Configurations - 2

28. Examples of Firewall Configurations - 2
Screened host firewall, Single-homed bastion
A firewall set up consists of two parts
The packet filter ensures that the incoming traffic is allowed only if it is destined for the application gateway, and it also ensures that the outgoing traffic is allowed only if it is originating from the application gateway.
The application gateway performs authentication and proxy functions.

29. Examples of Firewall Configurations - 3
This configuration increases the security of the network by performing checks at both packet and application levels.
One big disadvantage here is that the internal users are connected to the application gateway, as well as to the packet filter.
If the packet filter security its compromised, then the whole internal network is exposed to the attacker.

30. Examples of Firewall Configurations - 4

31. Examples of Firewall Configurations - 5
Screened host firewall, Dual-homed bastion
Direct connections between the internal hosts and the packet filter are avoided.
Instead, the packet filter connects only
to the application gateway, which, in turn, has a separate connection with the internal hosts.
Therefore, now even if the packet filter is successfully attacked, only the application gateway is visible to the attacker.
The internal hosts are protected.

32. Examples of Firewall Configurations - 6

33. Examples of Firewall Configurations - 7
Screened subnet firewall
It offers the highest security
Two packet filters are used
There are three levels of security for an attacker to break into.

34. Bastion Host The bastion host sits on the internal network.
It is the machine that will be accessed by all entities trying to access or leave the network.
It is the only system on the internal network that hosts on the Internet can open connections to (for example, to deliver incoming ).
If the bastion host is compromised, the internal network is wide open to attack from this bastion host
The bastion host thus needs to maintain a high level of host security.

35. Demilitarized Zone (DMZ) - 1
Another firewall features is provision of DMZ
DMZ - Demilitarized Zone:
Firewall configuration that allows an organization to securely host its public servers and also protect its internal network at the same time.
DMZ is simply a network segment that is located between the protected and the unprotected networks.
Fig 18.7

36. General DMZ rules - 1

37. General DMZ rules - 2
Allow external users to access the appropriate services on DMZ systems.
DMZ systems should be severely restricted from accessing internal systems.
Internal uses can access the DMZ or external network as policy allows
No external users may access the internal system.

38. Demilitarized Zone (DMZ) - 2

39. Recap Two type of firewall
packet filter firewall
stateless and stateful inspection
proxy firewall:
application level
not allow client to go directly, must go thru’ a proxy which has rules
Three basic configuration examples:
Screened host firewall, Single-homed bastion
Screened host firewall, Dual-homed bastion
Screened subnet
A modern firewall usually have three interfaces: trusted, DMZ and untrusted

40. NAT Explained - 1
NAT hides internal IP addresses by converting all internal host addresses to the address of the firewall as packets are routed through the firewall.
NAT is also called IP masquerading.
Translates the IP addresses of internal hosts to hide them from outside monitoring.
Originally implemented to make more IP addresses available to private networks.

41. NAT Explained (2)
The firewall then retransmits the data payload of the internal host from its own address using a translation table to keep track of which sockets on the exterior interface equate to which sockets on the interior interface.
To the Internet, all the traffic on your network appears to be coming from one extremely busy computer.

42. NAT Process - in details

43. NAT Modes - 1 Four primary modes of NAT:
Dynamic Translation (also called Automatic, Hide Mode or IP Masquerade)
Wherein a large group of internal clients share a single or small group of internal IP addresses for the purpose of hiding their identities or expanding the internal network address space.
Static Translation (also called Port Forwarding)
Wherein a specific internal network resource (usually a server) has a fixed translation that never changes. Static NAT is required to make internal hosts available for connections from external hosts.

44. NAT Modes - 2 Loading Balancing Translation
Wherein a single IP address and port is translated to a pool of identically configured servers so that a single public address can be served by a number of servers.
Network Redundancy Translation
Wherein multiple Internet connections are attached to a single NAT firewall and clients requests are routed through an Internet connection based on load and availability.

45. NAT used in ISP
A large group of internal clients share a single or small group of internal IP addresses for the purpose of hiding their identities or expanding the internal network address space.

46. Loading Balancing Translation
A single IP address and port is translated to a pool of identically configured servers so that a single public address can be served by a number of servers.

47. Hacking through NAT - 1
Static translation does not protect the internal host.
Static translation merely replaces port information on a one-to-one basis.
This affords no protection to statically translated hosts
Hacking attacks will be just as efficiently translated as any valid connection attempt.
Solution: Reduce the number of attack to one, and then to use application proxy software or other application based security measures.

48. Hacking through NAT - 2
If the client establishes the connection, a return connection exists.
Even if hackers can’t get inside our network, you can’t prevent your users form going to the hackers.
Forged with a Web site link, a Trojan horse, or a seductive content Web site can entice your users to attach to a machine whose purpose is to glean information about your network.
Solution: Higher-level, application-specific proxies are once again the solution.

49. Firewall Products

50. Cisco PIX firewall - 1 The Cisco PIX firewall series
a high-performance, enterprise-class firewall product line within the Cisco firewall family.
with integrated hardware and software
delivers high security and network performance
scalable to meet different customer requirements
Product
PIX 525 & PIX for large enterprise
PIX for medium size company
PIX for SOHO

51. Cisco PIX firewall - 2 The PIX firewalls provide
stateful inspection firewall
IPsec and L2TP/PPTP-based VPNs
content filtering capabilities (limited)
integrated intrusion detection capabilities

52. Adaptive Security Algorithm (ASA)
Adaptive Security Algorithm (ASA) is the foundation on which the PIX Firewall is built.
It defines how PIX examines traffic passing through it and applies various rules to it.
The basic concept behind ASA is to keep track of the various connections being formed from the networks behind the PIX to the public network.
Information keep tracking include:
IP packet source and destination information
TCP sequence numbers and additional TCP flags
UDP packet flow and timers

53. Rule to restrict information flow in a PIX firewall
Data traveling from a more secure interface to a less interface (from high to low)
A translation (either static or dynamic) is required to allow traffic from a higher security to a lower security interface.
Data traveling from a less secure interface to a more secure interface (from low to high)
A conduit or an access list is required to permit the desired traffic. That is, traffic is not allowed unless allowed by the conduit command or access list
Data traveling from two interfaces with the same security level
No traffic flows between two interfaces with the same security level.

54. Rule to restrict information flow in a PIX firewall

55. PIX commands There are six basic commands in Cisco PIX:
nameif – assign a name to an interface
interface – interface configuration
ip address command – assign IP address
nat command – network address translation command to define the trusted source address to be translated (two variants: nat : dynamic NAT and static: static NAT)
global – The global command defines a pool of global addresses. The global addresses in the pool provide an IP address for each outbound connection, and for those inbound connections resulting from outbound connections.
route – define static route

56. Examples of PIX commands to setup NAT and packet filter
Allow only external connected to web server at DMZ
nameif ethernet0 outside security0
nameif ehternet1 inside secuirty100
naemif ethernet2 dmz security50
Interface ethernet0 auto
ip address outside
ip address inside
ip address dmz
/* for NAT: allow NAT to all inside, map to set one static addr to */
nat (inside)
global (outside) netmask
static (inside, outside)
/* for packet filter: allow all external network to web server */
access-list 80 permit TCP any host
access group 80 in interface outside
route outside

57. Intrusion Detection

58. Traditional Security Approach
The disciplines of computer security address three fundamental needs:
Prevention
Detection
Response
Traditional response to security risks
a series of preventive measures design to keep out unauthorized people
Firewall only concentrated on perimeter defense!
it is only part of the defense in computer security

59. Intrusion Detection Approach
Problem with perimeter defenses (use firewall only) is that most of the losses are attributable to insiders!
IDS provides damage assessment and threat identification capabilities just like their physical counterparts
the video cameras => IDS sensors
Intrusion detection tools are not only prevention devices, it is for detection
IDS is also an excellent deterrent.

60. What are IDS?
IDS are dedicated appliances or software-based components that monitor network traffic or individual computer activity with the goals of
Identifying malicious actions
Resource misuse
Attempts to gain unauthorized access
Attacks
Note with IDS, you still need firewalls, anti-virus software, security policies, and other types of control.

61. Capabilities of an IDS Event log analysis for insider threat detection
Security configuration management
Network traffic analysis for perimeter threat detection
File integrity checking
Three main classes of analysis in IDS:
signature analysis
statistical analysis
integrity analysis

62. Signature Analysis
Look for specific attacks against known weak points of a system. These attacks can be detected by watching for certain actions (certain pattern of action) being performed on certain objects.
IDS performs signature analysis on the information it obtains.
Signature analysis is pattern matching of system setting and user activities against a database of known attacks.
require an updated list of signature file (e.g. once every 2 weeks released by CERN etc)
Comparisons with anti-virus software
anti-virus to scan hostile pattern from memory and files (hard-disk)
IDS is to scan hostile pattern within a network

63. Statistical Intrusion Analysis
Based on observations of deviations from normal system usage.
Method:
Require to measure a baseline of statistics:
CPU utilization and network usage
User logins and its pattern (i.e. time-of-day)
File activity and so on (file type and size and time)
Alert administrator regarding any deviation from this baseline.

64. Integrity Analysis
Integrity analysis reveals whether a file or object has been altered. Such analysis often uses strong cryptographic hash algorithms to determine whether anything has been modified.
e.g. if an attacker adds a user to a Linux system, the hash of the /etc/password file will change, alerting the administrator that the file has been modified.
e.g. Tripwire: digest are generated as a series markers. System can check all files again with the designated digest to check any modification. Unexpected change signify possible intrusion.
Tripwire is an open-source project of Purdue University (

65. Characteristics of a Good IDS
Run continually without supervision.
Be fault-tolerant.
Do not use excessive system resources.
Able to observe deviation from normal behavior.
Able to cope with changing system behavior over time. As new applications are added, the system profile will change automatically, and the IDS must be able to adapt.
Be accurate (0% false positive and 0% false negative).
Be customizable.
Be current (i.e. signature files and baseline data are up-to-date)

66. Errors in IDS - 1 False Positives
occurs when the IDS classifies an action as anomalous (a possible intrusion) when it is actually a legitimate action.
if too many false positives are generated, people will begin to ignore the output of the system, which might lead to an actually intrusion being detected but ignored.
problem: very difficult and often cannot totally eliminated.
output
FRR
reject
FAR
accept
input quality
(biometrics / IDS)
poor good
FAR – False Accept Rate
FRR – False Reject Rate

67. Errors in IDS - 2 False Negatives
occurs when an intrusive action has taken place, but the IDS allows it to pass as an non-intrusive behavior.
problem: Extremely dangerous
false negative subversion occurs when an intruder modifies the operation of the IDS to force false negatives to occur.

68. Categories of Intrusion Detection
Several categories of IDS exists in the market
NIDS - Network Intrusion Detection System (typical)
HIDS - Host Intrusion Detection System
Application Intrusion Detection System
Integrity Intrusion Detection (not yet popular)
e.g. Tripwire

69. NIDS - 1
Network-based IDS can be hardware appliances or software application installed on a computer system.
NIC works in promiscuous mode and collects and monitors network traffic for malicious activity.
There are sensors placed in the network segment that are to be monitored , typical strategic locations are: DMZ, behind firewall, database server’s subnet etc
These sensors are all connected to a central management console.
The traffic is then analyzed.

70. NIDS - 2 NIDS are mostly signature-based.
A set of attack signatures are built into the systems
These signatures are compared against the traffic on the network.
The NIC card that monitors the network in placed in “stealthy” mode so that it does not have an IP address and does not respond to probes such as a ping.
Add Fig 13-2

71. NIDS - 3 Advantages include
Lower cost of ownership (one IDS for whole networks)
The NIDS can be completely hidden on the network so that an attacker will not know that s/he is being monitored.

72. NIDS - 4 Disadvantages include:
The NIDS can only alarm if the traffic matches signatures
The NIDS cannot determine if the attack was successful
The NIDS cannot examine traffic that is encrypted
Switched network require special configurations
Unable to handle high-speed networks

73. HIDS - 1
Host-based IDS is a system of sensors that are loaded onto various servers within an organization and controlled by some central manager.
HIDS sensors watch the events associated with the server on which they are loaded.
The HIDS sensor can determine whether an attack was successful or not since the attack was on the same platform as the sensors.

74. HIDS - 2 The five basic types of HIDS sensors:
Log analyzers – looks for log entries that may indicate a security event.
Signature-based sensors – analyze incoming traffic and compare them with a set of built-in security event signatures
System call analyzers – examine an application’s system calls, analyze the action and compared it to a database of signatures.
Application behavior analyzers – the sensor examines an application’s system calls to see if it is allowed to perform such action.
File integrity checkers – check for changes in files.

75. HIDS - 3 Advantages: Verifies success or failure of an attack
Monitor specific system activities
Detect attacks that network-based systems miss
Well-suited for encrypted and switched environments
Requires no additional hardware
Lower cost of entry (for system with fewer number of hosts)

76. HIDS - 4
Disadvantages
Network activity is not visible to host-based sensors
Running audit mechanisms can use additional resources
When audit trails are used as data sources, they can take up significant storage
Host-based sensors must be platform specific
Management and deployment very difficult in large network

77. Designing Intrusion Detection Systems
Monitoring security through IDS requires a combination of:
good sensor placement
well designed sensor behaviour,
appropriate sensor configuration,
regular tuning and
a sound strategy for event response.

78. Application Intrusion Detection
Collects information at the application level.
E.g. Logs generated by database management software, Web servers, and firewalls. Sensors placed in the application collected and analyze information.
Not very popular at the moment
But it is expected in the coming years the focus on security will shift from network to server/application level.
Strength
High degree of control
Weakness
Too many applications to support
Covers only one component at a time

79. Popular IDS Products RealSecure Cisco Secure IDS Network ICE Snort
_detection/
Cisco Secure IDS
Network ICE
Snort

80. SNORT Light weight Network IDS
Packet capture /logger: real-time traffic analysis
Content search: detect attacks and probes
Support rule language
Detection engine with modular plug-ins
Real-time alerting capacity
Support Linux and Windows
Syslog features
logging network data in Tcpdump format
use WinPopup message to window client

81. SNORT (2) 4 major engines 3 modes packet capture / decode engine
rules parsing and detection engine
logging engine
plug-ins & preprocessing handling engine
3 modes
sniffing mode:
snort -v <= verbose to show header
snort -vd <= verbose to show header and data content
snort -vde <= same as above, with describe details
logging mode
snort –v –l ./log –h /24 <= for Linux
snort –v –l ..\log –h /24 <=for PC
IDS mode
snort –v –l ./log –h /24 –c snort.conf
snort –v –l ..\log –h /24 –c ..\etc\snort.conf

82. snort.conf - 1 To tune the performance of the NIDS Five sections
network and configuration variables
var HOME_NET
var HOME_NET [ , , 172, ]
var HOME_NET /24
var EXTERNAL_NET !HOME_NET
var ORACLE_PORTS 1512

83. snort.conf - 2 decoder and detection engine configuration
alert user if a packet has strange size, strange option, or uncommon setting
these are not necessary attacks and may generate large amount of false positive, use the following to disable, for example
config disable_decode_alerts
config disable_tcpopt_experimental_alerts

84. snort.conf - 3 preprocessor configuration
output configuration: control o/p format that works with 3rd party software
output alert_syslog: host= LOG_AUTH LOG_ALERT
output database: <log | alert>, <database type>, <parameter list>
file inclusions : include rule sets

85. preprocessor of SNORT - 1
functions of preprocessor
normalize traffic to ensure data packet can be watch by Snort
provide self-defense against attacks that may confuse or overwhelm an NIDS sensor
extend Snort’s ability to detect network anomalies (enhance the rule sets)

86. preprocessor of SNORT - 2
examples of preprocessor
flow - watches all traffic and keeps track of connections between machines. When a new unique flow is detected, the information is hashed and stored in a memory-resident table
frag2 - allow data fragment to be reassembled so that snort can see a “big picture”
examples
preprocessor flow: stats_interval 0 hash 2
perprocessor frag
other preprocessors: stream4, stream4_reassemble, HTTP_inspect, rpc_decode, bo, telnet decode, flow-portscan, arpspoof, perfmonitor

87. Typical rules in SNORT Rule header protocol field: ip, tcp, udp, icmp
action field: alert, log or pass
protocol field: ip, tcp, udp, icmp
rule field : src ip, src port, direction, dest ip, dest, port
e.g. alert tcp [ /19] 21:23 -> $HOME_NET any
e.g. log tcp $EXTERNAL_NET any -> $ $HOME_NET any (msg: “SCAN SYN FIN”, flags:SF; reference: arachnids, 198; classtype: attempted-recod; sid:624; rev:1;)
msg option : specify the type of attack
flags option: look for field of packet header (e.g. Syn, Fin)
reference: indicate where information can be found
class type option: category of attack
sid type option: signature ID
rev type option: rule revision number
simplest rule
alert tcp any any -> any any

88. pre-defined rules Snort come with a wide variety of rules
here are some examples
attack-responses.rules
backdoor.rules : detect traffic generated by backdoor connections such as netbus
dos.rules: detects traffic generated by known dos attacks, such as IGMP and teardrop attack
ddos.rules: alerts on traffic generated by well-down attacks such as trin00 and shaft. It can be noisy as it look for specific words in payload
dns.rules: alerts on attacks against DNS servers

89. Components of a typical SNORT system - 1
Snort sensors (the most important!!)
installed at strategic network locations
internal network, DMZ, and external network (sometimes)
snort only alert in log file
use tail -f to watch the log file, not very interactive
ACID : Analysis Console for Intrusion Databases
project developed by Roman Danyliw at US CERT coordination center
PHP based web application act as the front end of help to manage the alerts generated by multiple IDS sensors
generate trend, search based upon time, address, alert type, priority, classification and sensor

90. Components of a typical SNORT system - 2
MySQL: database server to store alerts and ready for analysis and inspection
Web Server: for hosting ACID web-based console that usually connected to a database
Web Browser: for user interface
Remote admin software to update sensor rules (optional)

91. Components of a typical SNORT system

92. IPS: Intrusion prevention system
A new class of security tool
place more focus on prevention
concepts & prevention strategies
host-based memory and process protection
kill process that appears malicious, or when it try to execute a buffer overflow (e.g. anti-spyware)
session interception
terminate a TCP session by sending RST packet to tear down connection, also known as session sniping
gateway intrusion detection
modify ACL to block hostile traffic automatically
e.g. SnortSAM

93. Honeypot - 1 Honeypot is a tool used commonly for network security
for computer crime forensic
it is a decoy IDS, part of the company resource waiting to be probed, attacked, or compromised.
it can be a decoy service, decoy host (I.e Honeypot) or decoy network (Honeynet)
They don't fix a single problem, instead they can help in prevention, detection, or information gathering.

94. Honeypot - 2
Honeypots are closely monitored network decoys serving several purposes:
distract hackers from more valuable machines on a network
provide early warning about new attack and exploitation trends
allow in-depth examination of adversaries during and after exploitation of a honeypot.
Honeypot should be highly secure and isolated by the rest of the network.
Decoy:誘餌;誘惑物

95. Summary - 1 Firewall modern FW: packet filter, proxy, NAT, VPN
packet-filter firewall: filters at the network or transport layer
stateless inspection (static packet filter)
stateful inspection (dynamic packet filter)
proxy firewall: filters at the application layer (many rules can be applied)
usually work with proxy servers to provide large hard-disk storage for content cache.

96. Summary - 2 NAT IDS solve the problem of IP address limitation
provide load balance and redundancy
Foure modes: Dynamic Translation (IP Masquerade), Static Translation (Port Forwarding), Loading Balancing Translation and Network Redundancy Translation
IDS
active detection to monitor the network status
three methods: signature, statistical and integrity
four types: network, host, applications and integrity