Reference Manual

NAME

smap - specify special port mappings
SYNOPSIS
smap
smap add tcp|udp src_port src_IP new_src_port
smap delete tcp|udp src_port
DESCRIPTION
Command smap controls special port mapping. Special port mappings are used to make designated source ports on designated private machines map to a designated new source port, thereby overriding the default port mapping mechanism. This feature is useful for networking applications which explicitly choose a source port for packet transmission and then listen for responses arriving at that port.

If no argument is specified, the current state of the special port mapping table is printed as follows:

Index - the table index
Proto - the protocol type (UDP or TCP)
SrcPort - the source port number to be mapped
SrcIP - the source address of the mapping
NewSrcPort - the new source port number
If the add argument is specified, four further arguments are required:

tcp or udp - the desired protocol
src_port - the source port number to be mapped for a specified private host
src_IP - the IP address of the private host
new_src_port - the new source port number to be used

Example: smap add udp 4686 192.168.1.10 4686

The above command will make NAT32 map UDP traffic from private host 192.168.1.10 from port 4686 appear to have come from Port 4686. In other words, NAT32 will preserve the source port number for this host and port. Incoming traffic to Port 4686 will be forwarded to host 192.168.1.10.

If the delete argument is specified, the entry for the specified protocol and port number is deleted from the table.

NOTES
Use Special Port Mapping with care because it gives external hosts access to servers on your private machines. Be sure you have set strong passwords on all services which you present to the Internet.

Only one private host may use a particular Special Port Mapping at a time. If other private hosts are running the same application, the user must configure the application on the other hosts to use a different source port number. Details on how to do this are application-specific and can often be found in the vendor's help files or WWW pages.

You do not need to add Special Port Mappings for applications such as ICQ, which assume that UDP mappings are permanently stored in the Port Mapping Table of a NAT. See command umap for details on how to support such applications.

SEE ALSO
icmap, pmap, ppmap, umap