Service Types - D-Link DFL-1600 User Manual
Network security firewall
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Chapter 8. Logical Objects
one user's program to other parties in a network. At this layer, other
parties are identified and can be reached by specific
and corresponding parameters, such as
. For
example, the Web-browsing service HTTP is defined as to use the TCP
protocol with destination port 80. Some of the other popular services at this
layer include FTP, POP3, SMTP, Telnet, and so on. Beside these officially
defined applications, user customized services can also be created in D-Link
firewalls.
Services are simplistic, in that they cannot carry out any action in the
firewall on their own. Thus, a service definition does not include any
information whether the service should be allowed through the firewall or
not. That decision is made entirely by the firewall's IP rules, in which the
service is used as a filter parameter. For more information about how to
use services in rules, please see
14 IP
Rules.
8.2.1
Service Types
In D-Link firewalls, services can be configured via three options:
TCP/UDP, ICMP, and IP Protocol service. A service is basically defined
by a descriptive name, the type of the protocol, and protocol parameters.
Different services can be united into one Service Group to simplify policy
configuration, so that the administrators do not need to configure one rule
for every service.
TCP and UDP based services
Service applications most commonly run on TCP or UDP, and are often
associated with a well-known port number. In the firewall, they are defined
by the type of protocol that the application uses, and the assigned port
number or port range. For many services, a single
is
sufficient. The HTTP service, for instance, uses TCP destination port 80,
Telnet uses TCP 23, and SMTP uses TCP 25. In these cases, all ports
(0-65535) will be accepted as source ports.
Multiple
or
may also be set, for instance, a service can
be defined as having source ports 1024-65535 and destination ports 80-82,
90-92, 95. In this case, a TCP or UDP packet with the destination port
being one of 80, 81, 82, 90, 91, 92 or 95, and the source port being in the
range 1024-65535, will match this service.
D-Link Firewalls User's Guide
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