Reference Manual


setis - interact with the Interface Selection mechanism
setrr - interact with the Record Routes mechanism
setis [algorithm]
setrr [on | off]
setx ifn [0 | 1]


When invoked with no argument, setis prints details of the current algorithm used for selecting a default route to the Internet.

Argument algorithm can have one of the following values:

    0    Use the interface with the best metric
    1    Use the main interface only
    2    Use the auxiliary interface only
    3    Use the interface with the lowest usage
    4    Use the interface with the highest capacity
    5    Enable TURBO mode
    6    Use the auxiliary interface for source routes only

If algorithm 1, 2, 3, 4, 5 or 6 is selected, the command also turns on the Record Routes option. This setting can be modified with the command:

setrr [on | off]

The selected algorithm is not recorded in any configuration file or in the Windows Registry. To make the selection permanent, the needed command should be placed in file user.txt.

Changing the interface selection algorithm resets all counters that the new algorithm uses and clears ALL port mappings.


NAT32 Connection Aggregation allows multiple connections to be shared by all machines. It also allows certain connections to be reserved for use by specific machines or subnets. Because of this route selection by source address capability, NAT32 connection aggregation is superior to other forms of connection aggregation such as Multilink, which require ISP support and which cannot allocate traffic to connections dynamically.

Note that connection aggregation increases total throughput only. It does not increase connection speed. Connection aggregation can increase the total number of packets per second being transferred, but each packet is transferred at the speed supported by the connection it is using.

The NAT32 Primary (or Main) Interface is the default Internet-connected interface used to send and receive packets from the Internet. There must exist a default route for that interface.

The Primary interface can be set with the setp command, but it defaults to the interface for which the Main Internet Adapter checkbox was checked in the Interface Configuration dialog.

When several Internet-connected interfaces are available, only outgoing TCP connections can be forwarded via an alternative interface. All other traffic continues to be forwarded via the interface with the best metric (algorithm 0) or the Main interface (algorithm 1). An exception to this rule applies for VPN connections. If a host has issued a route vpn command, then all its Internet traffic is forwarded via the VPN connection. Note that this includes DNS name lookups, which are forwarded to the VPN connection's DNS server.

When several Internet-connected interfaces are available, and algorithm 1, 2, 3, 4, 5 or 6 is selected, outgoing TCP connections cause a host-specific and source-specific route to be added to the NAT32 Routing Table. This ensures that all traffic to the same IP address from the same source address is routed via the same interface. The route is deleted when all port mappings that reference it have been deleted. The mechanism can be overridden with the command:

setrr [on | off]

Algorithm 3 attempts to spread traffic (input plus output) evenly over all Internet interfaces. Although this is not always possible (because of routing requirements), the traffic will even out over the longer term. To view the current interface usage, the command: routes count can be used.

Algorithm 4 attempts to route traffic over all Internet interfaces according to their current capacity. The capacity of an interface is independent of the physical interface speed. It is calculated by measuring the current throughput of an interface and comparing it to the previous throughput of the interface. For example, if the current throughput equals the previous throughput, the current capacity of the interface is deemed to be 0%. If the current throughput is 30% of the previous throughput, the current capacity is deemed to be 70%.

Algorithm 5 sets a Turbo Mode that allows an Auxiliary interface to be used to boost network throughput whenever the current capacity of the Main interface falls below a certain threshold (default 10%). This mode is typically used when 3G, 4G or LTE mobile broadband interfaces are available, that are to be used only when more throughput is needed. The environment variable turbo holds the threshold value, and setting it higher will cause the Auxiliary interface to be used more often. Setting the threshold lower will cause that interface to be used less frequently.

Algorithm 6 enforces the use of Source Routing on the Auxiliary interface. The algorithm ensures that only computers that have a source route entry in the NAT32 routing table will use the interface for Internet traffic.

The Source Route mechanism (if enabled) overrides the Interface Selection mechanism.

Route selection can also be modified by adding a Protocol and Destination Port specific route to the Routing Table. Such routes are often better matches than the default route for an interface and will therefore be chosen in preference to a default route. This mechanism cannot be used to bypass the Source Route mechanism.

Algorithms 1, 2, 3, 4, 5 and 6 honor the exclude flag, that forces an interface to be skipped by the above algorithms. The flag can be modified with the command:

setx ifn [0 | 1]
netcfg, route, sethtx, setgs, setsr