Services; Overview - D-Link DFL-1660 User Manual

3.3. Services

3.3. Services

3.3.1. Overview

A Service object is a reference to a specific IP protocol with associated parameters. A service
definition is usually based on one of the major transport protocols such as TCP or UDP which is
associated with a specific source and/or destination port number(s). For example, the HTTP service
is defined as using the TCP protocol with the associated destination port 80 and any source port.
However, service objects are not restricted to just the TCP or UDP protocols. They can be used to
encompass ICMP messages as well as a user-definable IP protocol.
A Service is Passive
Services are passive NetDefendOS objects in that they do not themselves carry out any action in the
configuration. Instead, service objects must be associated with the security policies defined by
various NetDefendOS rule sets and then act as a filter to apply those rules only to a specific type of
traffic.
For example, an IP rule in a NetDefendOS IP rule set has a service object associated with it as a
filtering parameter to decide whether or not to allow a specific type of traffic to traverse the
NetDefend Firewall. Inclusion in IP rules is one the most important usage of service objects and it is
also how ALGs become associated with IP rules since an ALG is associated with a service and not
directly with an IP rule.
For more information on how service objects are used with IP rules, see Section 3.6, "IP Rules".
Predefined Services
A large number of service objects are predefined in NetDefendOS. These include common services
such as HTTP, FTP, Telnet and SSH.
Predefined services can be used and also modified just like custom, user defined services. However,
it is recommended to NOT make any changes to predefined services and instead create custom
services with the desired characteristics.
Custom service creation in detail later in Section 3.3.2, "Creating Custom Services".
Example 3.11. Listing the Available Services
To produce a listing of the available services in the system:
Command-Line Interface
gw-world:/> show Service
The output will look similar to the following listing with the services grouped by type with the service groups
appearing first:
ServiceGroup
Name
------------
all_services
all_tcpudp
ipsec-suite
l2tp-ipsec
l2tp-raw
pptp-suite
ServiceICMP
Comments
--------------------------------------------------
All ICMP, TCP and UDP services
All TCP and UDP services
The IPsec+IKE suite
L2TP using IPsec for encryption and authentication
L2TP control and transport, unencrypted
PPTP control and transport
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Chapter 3. Fundamentals