SMARTLINK
I&II
MDS921AE-10BTS - MDS
Firewall
A firewall protects networked computers from intentional hostile intrusion that could compromise
confidentiality or result in data corruption or denial of service. It must have at least two network
interfaces, one for the network it is intended to protect,
firewall sits at the junction point or gateway between the two networks, usually a private network
and a public network such as the Internet.
A firewall examines all traffic routed between the two networks to
does, it is routed between the networks, otherwise it is stopped. A firewall filters both inbound and
outbound traffic. It can also manage public access to private networked resources such as host
applications. It can be used to log all attempts to enter the private network and trigger alarms when
hostile or unauthorized entry is attempted. Firewalls can filter packets based on their source and
destination addresses and port numbers. This is known as address filtering
filter specific types of network traffic. This is also known as protocol filtering because the decision
to forward or reject traffic is
Firewalls can also filter traffic by packet attribute or state.
An Internet firewall cannot prevent individual users with modems from
network. By doing so they bypass the firewall altogether. Employee misconduct or carelessness
cannot be controlled by firewall
accounts must be strictly enforced. These are management issues that should be raised during
the planning of any security policy, but that cannot be solved with Internet firewalls alone.
Types of Firewall
There are three types of firewall:
Packet Filtering
In packet filtering, only the protocol and the address information of each packet is examined. Its
contents and context (its relation to other packets and to the intended application) are
The firewall pays no attention to applications on the host or local network and it "knows" nothing
about the sources of incoming data. Filtering consists of examining incoming or outgoing packets
and allowing or disallowing their transmission or a
rules. Network Address Translation (NAT) routers offer the advantages of packet filtering firewalls
but can also hide the IP addresses of computers behind the firewall, and offer a level of
circuit-based filtering.
Circuit Gateway
Also called a "Circuit Level Gateway," this is a firewall approach that validates connections before
allowing data to be exchanged. What this means is that the firewall doesn't simply allow or
disallow packets but also determines wh
according to configurable rules, then opens a session and permits traffic only from the allowed
source and possibly only for a limited period of time.
Application Gateway
The Application Level Gateway acts
with the remote system in their behalf. This can render a computer behind the firewall all but
invisible to the remote system. It can allow or disallow traffic according to very specific rules, for
instance permitting some commands to a server but not others, limiting file access to certain types,
varying rules according to authenticated users and so forth. This type of firewall may also perform
very detailed logging of traffic and monitoring of eve
instructed to sound alarms or notify an operator under defined conditions. Application
gateways are generally regarded as the most secure type of firewall. They certainly have the most
sophisticated capabilities.
S957AE-10BTS User Manual
Page 11 of 113
A firewall protects networked computers from intentional hostile intrusion that could compromise
confidentiality or result in data corruption or denial of service. It must have at least two network
interfaces, one for the network it is intended to protect, and one for the network it is exposed to. A
firewall sits at the junction point or gateway between the two networks, usually a private network
and a public network such as the Internet.
A firewall examines all traffic routed between the two networks to see if it meets certain criteria. If it
does, it is routed between the networks, otherwise it is stopped. A firewall filters both inbound and
outbound traffic. It can also manage public access to private networked resources such as host
n be used to log all attempts to enter the private network and trigger alarms when
hostile or unauthorized entry is attempted. Firewalls can filter packets based on their source and
destination addresses and port numbers. This is known as address filtering
filter specific types of network traffic. This is also known as protocol filtering because the decision
to forward or reject traffic is dependent upon the protocol used, for example HTTP, ftp or telnet.
c by packet attribute or state.
An Internet firewall cannot prevent individual users with modems from dialing
network. By doing so they bypass the firewall altogether. Employee misconduct or carelessness
cannot be controlled by firewalls. Policies involving the use and misuse of passwords and user
accounts must be strictly enforced. These are management issues that should be raised during
the planning of any security policy, but that cannot be solved with Internet firewalls alone.
There are three types of firewall:
In packet filtering, only the protocol and the address information of each packet is examined. Its
contents and context (its relation to other packets and to the intended application) are
The firewall pays no attention to applications on the host or local network and it "knows" nothing
about the sources of incoming data. Filtering consists of examining incoming or outgoing packets
and allowing or disallowing their transmission or acceptance on the basis of a set of configurable
rules. Network Address Translation (NAT) routers offer the advantages of packet filtering firewalls
but can also hide the IP addresses of computers behind the firewall, and offer a level of
Also called a "Circuit Level Gateway," this is a firewall approach that validates connections before
allowing data to be exchanged. What this means is that the firewall doesn't simply allow or
disallow packets but also determines whether the connection between both ends is valid
according to configurable rules, then opens a session and permits traffic only from the allowed
source and possibly only for a limited period of time.
The Application Level Gateway acts as a proxy for applications, performing all data exchanges
with the remote system in their behalf. This can render a computer behind the firewall all but
invisible to the remote system. It can allow or disallow traffic according to very specific rules, for
instance permitting some commands to a server but not others, limiting file access to certain types,
varying rules according to authenticated users and so forth. This type of firewall may also perform
very detailed logging of traffic and monitoring of events on the host system, and can often be
instructed to sound alarms or notify an operator under defined conditions. Application
gateways are generally regarded as the most secure type of firewall. They certainly have the most
A firewall protects networked computers from intentional hostile intrusion that could compromise
confidentiality or result in data corruption or denial of service. It must have at least two network
and one for the network it is exposed to. A
firewall sits at the junction point or gateway between the two networks, usually a private network
see if it meets certain criteria. If it
does, it is routed between the networks, otherwise it is stopped. A firewall filters both inbound and
outbound traffic. It can also manage public access to private networked resources such as host
n be used to log all attempts to enter the private network and trigger alarms when
hostile or unauthorized entry is attempted. Firewalls can filter packets based on their source and
destination addresses and port numbers. This is known as address filtering. Firewalls can also
filter specific types of network traffic. This is also known as protocol filtering because the decision
upon the protocol used, for example HTTP, ftp or telnet.
dialing into or out of the
network. By doing so they bypass the firewall altogether. Employee misconduct or carelessness
s. Policies involving the use and misuse of passwords and user
accounts must be strictly enforced. These are management issues that should be raised during
the planning of any security policy, but that cannot be solved with Internet firewalls alone.
In packet filtering, only the protocol and the address information of each packet is examined. Its
contents and context (its relation to other packets and to the intended application) are ignored.
The firewall pays no attention to applications on the host or local network and it "knows" nothing
about the sources of incoming data. Filtering consists of examining incoming or outgoing packets
cceptance on the basis of a set of configurable
rules. Network Address Translation (NAT) routers offer the advantages of packet filtering firewalls
but can also hide the IP addresses of computers behind the firewall, and offer a level of
Also called a "Circuit Level Gateway," this is a firewall approach that validates connections before
allowing data to be exchanged. What this means is that the firewall doesn't simply allow or
ether the connection between both ends is valid
according to configurable rules, then opens a session and permits traffic only from the allowed
as a proxy for applications, performing all data exchanges
with the remote system in their behalf. This can render a computer behind the firewall all but
invisible to the remote system. It can allow or disallow traffic according to very specific rules, for
instance permitting some commands to a server but not others, limiting file access to certain types,
varying rules according to authenticated users and so forth. This type of firewall may also perform
nts on the host system, and can often be
instructed to sound alarms or notify an operator under defined conditions. Application-level
gateways are generally regarded as the most secure type of firewall. They certainly have the most
