D-Link DFL-260E User Manual page 277

6.2.8. The SIP ALG
If Record-Route is enabled then the Source Network for outbound traffic from proxy users can be
further restricted in the above rules by using "ip_proxy" as indicated.
When an incoming call is received, the SIP ALG will follow the SAT rule and forward the SIP
request to the proxy server. The proxy will in turn, forward the request to its final destination which
is the client.
If Record-Route is disabled at the proxy server, and depending on the state of the SIP session, the
SIP ALG may forward inbound SIP messages directly to the client, bypassing the SIP proxy. This
will happen automatically without further configuration.
Solution B - Without NAT
Without NAT, the outbound NAT rule is replaced by an Allow rule. The inbound SAT and Allow
rules are replaced by a single Allow rule.
OutboundFrom
Proxy&Clients
InboundTo
Proxy&Clients
If Record-Route is enabled then the networks in the above rules can be further restricted by using
"(ip_proxy)" as indicated.
Scenario 3
Protecting proxy and local clients - Proxy on the DMZ interface
This scenario is similar to the previous but the major difference is the location of the local SIP proxy
server. The server is placed on a separate interface and network to the local clients. This setup adds
an extra layer of security since the initial SIP traffic is never exchanged directly between a remote
endpoint and the local, protected clients.
The complexity is increased in this scenario since SIP messages flow across three interfaces: the
receiving interface from the call initiator, the DMZ interface towards the proxy and the destination
interface towards the call terminator. This the initial messages exchanges that take place when a call
is setup in this scenario are illustrated below:
Action Src Interface
Allow lan
Allow wan
277
Chapter 6. Security Mechanisms
Src Network Dest Interface
lannet wan
(ip_proxy)
all-nets lan
Dest Network
all-nets
lannet
(ip_proxy)