6.2. ALGs
6.2.1. Overview
To complement low-level packet filtering, which only inspects packet headers in protocols such as
IP, TCP, UDP, and ICMP, NetDefend Firewalls provide Application Layer Gateways (ALGs) which
provide filtering at the higher application OSI level.
An ALG object acts as a mediator in accessing commonly used Internet applications outside the
protected network, for example web access, file transfer and multimedia transfer. ALGs provide
higher security than packet filtering since they are capable of scrutinizing all traffic for a specific
protocol and perform checks at the higher levels of the TCP/IP stack.
ALGs exist for the following protocols in NetDefendOS:
•
HTTP
•
FTP
•
TFTP
•
SMTP
•
POP3
•
SIP
•
H.323
•
TLS
Deploying an ALG
Once a new ALG object is defined by the administrator, it is brought into use by first associating it
with a Service object and then associating that service with an IP rule in the NetDefendOS IP rule
set.
Figure 6.1. Deploying an ALG
6.2. ALGs
Chapter 6. Security Mechanisms
245
Summary of Contents for DFL-1600 - Security Appliance
Page 27: ...1 3 NetDefendOS State Engine Packet Flow Chapter 1 NetDefendOS Overview 27 ...
Page 79: ...2 7 3 Restore to Factory Defaults Chapter 2 Management and Maintenance 79 ...
Page 146: ...3 9 DNS Chapter 3 Fundamentals 146 ...
Page 227: ...4 7 5 Advanced Settings for Transparent Mode Chapter 4 Routing 227 ...
Page 241: ...5 4 IP Pools Chapter 5 DHCP Services 241 ...
Page 339: ...6 7 Blacklisting Hosts and Networks Chapter 6 Security Mechanisms 339 ...
Page 360: ...7 4 7 SAT and FwdFast Rules Chapter 7 Address Translation 360 ...
Page 382: ...8 3 Customizing HTML Pages Chapter 8 User Authentication 382 ...
Page 386: ... The TLS ALG 9 1 5 The TLS Alternative for VPN Chapter 9 VPN 386 ...
Page 439: ...Figure 9 3 PPTP Client Usage 9 5 4 PPTP L2TP Clients Chapter 9 VPN 439 ...
Page 450: ...9 7 6 Specific Symptoms Chapter 9 VPN 450 ...
Page 488: ...10 4 6 Setting Up SLB_SAT Rules Chapter 10 Traffic Management 488 ...
Page 503: ...11 6 HA Advanced Settings Chapter 11 High Availability 503 ...
Page 510: ...12 3 5 Limitations Chapter 12 ZoneDefense 510 ...
Page 533: ...13 9 Miscellaneous Settings Chapter 13 Advanced Settings 533 ...