Protocol-independent settings
Allow ICMP errors from the destination to the source
– ICMP error messages are sent
in several situations: for example, when an IP packet cannot reach its destination. The
purpose of these error control messages is to provide feedback about problems in the
communication environment.
However, ICMP error messages and firewalls are usually not a very good combination; the
ICMP error messages are initiated at the destination host (or a device within the path to the
destination) and sent to the originating host. The result is that the ICMP error message will be
interpreted by the firewall as a new connection and dropped, if not explicitly allowed by the
firewall rule-set. It is generally not a good idea to allow any inbound ICMP message to be able
to have those error messages forwarded.
To solve this problem, the DFL-700 can be instructed to pass an ICMP error message only
if it is related to an existing connection. Check this option to enable this feature for
connections using this service.
ALG
– Similar to the way most stateful inspection firewalls behave, the DFL-700 filters
only information found in packet headers, such as IP, TCP, UDP, or ICMP headers.
In some situations though, filtering only header data is not sufficient. The FTP protocol, for
instance, includes IP address and port information in the protocol payload. In these cases, the
firewall needs to be able to examine the payload data and carry out appropriate actions. The
DFL-700 provides this functionality using Application Layer Gateways (ALG).
To use an Application Layer Gateway, the appropriate Application Layer Gateway
definition is selected in the dropdown menu. The selected Application Layer Gateway will thus
manage network traffic that matches the policy using this service.
Currently, the DFL-700 supports two Application Layer Gateways, one is used to manage
the FTP protocol and the other one is a HTTP Content Filtering ALG. For detailed information
about how to configure the HTTP Application Layer Gateway, please see the Content Filtering
chapter.
Summary of Contents for DFL-700 - Security Appliance
Page 1: ...D Link DFL 700 Network Security Firewall Manual Building Networks for People 04 18 2005 TM ...
Page 102: ...102 5 Select Connect to the network at my workplace and click Next ...
Page 103: ...6 Select Virtual Private Network connection and click Next ...
Page 104: ...104 7 Name the connection MainOffice and click Next ...
Page 105: ...8 Select Do not dial the initial connection and click Next ...
Page 106: ...106 9 Type the IP address to the server 194 0 2 20 and click Next 10 Click Finish ...