1. Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft
Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft
Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft

2. Firewalls
 What is a Firewall
 Types of Firewalls
 Network Layer
 Application Layer
 Network Address Translations
 Appropriate use of Firewalls
 Configuration considerations

3. What is a Firewall
 A firewall's basic task is to transfer traffic between computer networks
of different trust levels.Typical examples are the Internet which is a
zone with no trust and an internal network which is a zone of higher
trust. A zone with an intermediate trust level, situated between the
Internet and a trusted internal network, is often referred to as a
"perimeter network" or Demilitarized zone (DMZ).

4.  A firewall's function within a network is similar to firewalls in
building construction, because in both cases they are intended to
isolate one "network" or "compartment" from another. However,
network firewalls, unlike physical firewalls, are designed to allow some
traffic to flow.
What is a Firewall

5.  Without proper configuration, a firewall can often become
worthless. Standard security practices dictate a "default-deny"
firewall ruleset, in which the only network connections which are
allowed are the ones that have been explicitly allowed.
Unfortunately, such a configuration requires detailed
understanding of the network applications and endpoints
required for the organization's day-to-day operation. Many
businesses lack such understanding, and therefore implement a
"default-allow" ruleset, in which all traffic is allowed unless it has
been specifically blocked. This configuration makes inadvertent
network connections and system compromise much more likely.
What is a Firewall

6. Types of Firewalls

7. Types of Firewalls
 Network layer firewalls, also called packet filters, operate at a relatively
low level of theTCP/IP protocol stack
 They will not allow packets to pass through the firewall unless they
match the established ruleset.The firewall administrator may define
the rules; or default rules may apply.

8.  Network layer firewalls generally fall into two sub-categories, stateful and
stateless.
 Stateful firewalls maintain context about active sessions, and use that "state
information" to speed up packet processing. Any existing network
connection can be described by several properties, including source and
destination IP address, UDP orTCP ports, and the current stage of the
connection's lifetime (including session initiation, handshaking, data
transfer, or completion connection. If a packet does not match an existing
connection, it will be evaluated according to the ruleset for new connections.
If a packet matches an existing connection based on comparison with the
firewall's state table, it will be allowed to pass without further processing.
Types of Firewalls

9.  Application-layer firewalls work on the application level of theTCP/IP
stack (i.e., all browser traffic, or all telnet or ftp traffic), and may intercept
all packets traveling to or from an application.They block other packets
(usually dropping them without acknowledgement to the sender). In
principle, application firewalls can prevent all unwanted outside traffic from
reaching protected machines.
 By inspecting all packets for improper content, firewalls can restrict or
prevent outright the spread of networked computer worms and trojans. In
practice, however, this becomes so complex and so difficult to attempt (given
the variety of applications and the diversity of content each may allow in its
packet traffic) that comprehensive firewall design does not generally attempt
this approach
Types of Firewalls

10. Network AddressTranslation (NAT, also known as Network
Masquerading, Native AddressTranslation or IP Masquerading)
involves re-writing the source and/or destination addresses of IP
packets as they pass through a Router or firewall. Most systems using
NAT do so in order to enable multiple hosts on a private network to
access the Internet using a single public IP address. Many network
administrators find NAT a convenient technique and use it widely.
Nonetheless, NAT can introduce complications in communication
between hosts and may have a performance impact
Types of Firewalls

11.  Network AddressTranslation
 One-to-One (One private address for One public address)
 Geared for applications that require use of many ports/apps (i.e. ftp, www,
8081).
 Port AddressTranslation
 One-to-many (One public IP address is used, but specific ports are translated).
 Geared for applications that only need 1 port in connection (i.e. basic web
servers, e-mail).
Types of Firewalls

12. Appropriate use of Firewalls
 Firewalls are applicable when –
 When there is two networks that have a distinct trust factor (friend/foe).
 When network topology is designed to flow all traffic thru a single
interface which connects to the firewall (i.e. protected networks
connection must terminate behind firewall).
 When there is need for extra layer of protection for certain applications.

13.  Firewalls are NOT applicable when
 When applications that transverse two networks are QoS sensitive.
 Vendors use scare tactics and not give a qualified reason for firewall.
 When you are only support and haven’t been trained.
 When application/resource accessibility is more critical than security
(timing).
Appropriate use of Firewalls

14. Configuration Considerations
 By default, less trusted networks has NO access to the trusted network
(deny all).
 Be port specific as possible when allowing outside host to access
applications.
 Remember ANY means ANY in a firewall ruleset! Outside of web
and e-mail, this should not be used to allow access into applications.
 For vendor support, restrict access just to their network or IP Address.
 Certain applications are very firewall sensitive (i.e.Voice, H323 or any
QoS type apps).

15.  Firewalls does not encrypt data unless specifically programmed( IPSec
tunnel).
 Rulesets/access-list will not work unless applied to interface.
Configuration Considerations

16. Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft
Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft