Planet G.SHDSL.bis Bridge Router GRT-504, Руководство пользователя

Страница: 19 / 152

GRT-504 4-Wire G.SHDSL.bis Firewall Router User’s Manual
3.2.3 Application Gateway
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 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; furthermore 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
sophisticated capabilities.
Level 5: Application
Level 4: TCP
Level 3: IP
Level 2: Data Link
Level 1: Physical
Telnet
FTP
Http
SMTP
Host PC
Proxy Server
Public Server
Request Page
Check URL
Request Page
Return Page
Return Page
Filter Content
External
Interface
Internal
Interface
Proxy Application
18