Fortinet FortiGate Series Administration Manual page 448

How virtual IPs map connections through FortiGate units
448
When comparing packets with the firewall policy list to locate a matching policy, if a firewall
policy's Destination Address is a virtual IP, FortiGate units compares packets' destination
address to the virtual IP's external IP address. If they match, the FortiGate unit applies the
virtual IP's inbound NAT mapping, which specifies how the FortiGate unit translates
network addresses and/or port numbers of packets from the receiving (external) network
interface to the network interface connected to the destination (mapped) IP address or IP
address range.
In addition to specifying IP address and port mappings between interfaces, virtual IP
configurations can optionally bind an additional IP address or IP address range to the
receiving network interface. By binding an additional IP address, you can configure a
separate set of mappings that the FortiGate unit can apply to packets whose destination
matches that bound IP address, rather than the IP address already configured for the
network interface.
Depending on your configuration of the virtual IP, its mapping may involve port address
translation (PAT), also known as port forwarding or network address port translation
(NAPT), and/or network address translation (NAT) of IP addresses.
If you configure NAT in the virtual IP and firewall policy, the NAT behavior varies by your
selection of:
• static vs. dynamic NAT mapping
• the dynamic NAT's load balancing style, if using dynamic NAT mapping
• full NAT vs. destination NAT (DNAT)
The following table describes combinations of PAT and/or NAT that are possible when
configuring a firewall policy with a virtual IP.
Static NAT Static, one-to-one NAT mapping: an external IP address is always translated to
the same mapped IP address.
If using IP address ranges, the external IP address range corresponds to a
mapped IP address range containing an equal number of IP addresses, and
each IP address in the external range is always translated to the same IP
address in the mapped range.
Static NAT with Static, one-to-one NAT mapping with port forwarding: an external IP address is
always translated to the same mapped IP address, and an external port number
Port Forwarding
is always translated to the same mapped port number.
If using IP address ranges, the external IP address range corresponds to a
mapped IP address range containing an equal number of IP addresses, and
each IP address in the external range is always translated to the same IP
address in the mapped range. If using port number ranges, the external port
number range corresponds to a mapped port number range containing an equal
number of port numbers, and each port number in the external range is always
translated to the same port number in the mapped range.
Server Load Dynamic, one-to-many NAT mapping: an external IP address is translated to one
of the mapped IP addresses, as determined by the selected load balancing
Balancing
algorithm for more even traffic distribution. The external IP address is not always
translated to the same mapped IP address.
Server load balancing requires that you configure at least one "real" server, but
can use up to eight. Real servers can be configured with health check monitors.
Health check monitors can be used to gauge server responsiveness before
forwarding packets.
Server Load Dynamic, one-to-many NAT mapping with port forwarding: an external IP
address is translated to one of the mapped IP addresses, as determined by the
Balancing with
selected load balancing algorithm for more even traffic distribution. The external
Port Forwarding
IP address is not always translated to the same mapped IP address.
Server load balancing requires that you configure at least one "real" server, but
can use up to eight. Real servers can be configured with health check monitors.
Health check monitors can be used to gauge server responsiveness before
forwarding packets.
FortiGate Version 4.0 MR1 Administration Guide
01-410-89802-20090903
http://docs.fortinet.com/
Firewall Virtual IP
• Feedback