IBM SC41-5420-04 manual TCP/IP Port Restriction, Dftroute None

a specific route defined. The system allows up to eight default routes, but each route must have a unique next hop value.

An example of a multiple route table can be found in Figure 54.

Work with TCP/IP Routes

				System: SYSNAM003
Type options, press Enter.
1=Add	2=Change	4=Remove 5=Display
	Route	Subnet	Next	Preferred
Opt	Destination	Mask	Hop	Interface
_	______________	______________	______________
_	*DFTROUTE	*NONE	9.4.73.193	*NONE
_	*DFTROUTE	*NONE	9.4.73.197	*NONE
_	*DFTROUTE	*NONE	9.4.73.196	*NONE
_	9.4.70.0	255.255.255.0	9.4.73.194	*NONE
_	9.4.70.0	255.255.255.0	9.4.73.195	*NONE
_	9.4.70.0	255.255.255.0	9.4.73.198	*NONE

			Bottom
F3=Exit	F5=Refresh	F6=Print list	F10=Work with IP over SNA routes
F11= Display type of		service F12=Cancel	F17=Top F18=Bottom

Figure 54. Work with TCP/IP Routes Display

TCP/IP Port Restriction

TCP and UDP protocols use ports to identify a unique origin or destination of communication with an application. Each port is assigned a small integer. You can configure port information if you want to restrict the use of a TCP or UDP port to one or more user IDs.

The range of port numbers is from 1 to 65535. However, ports 0-1023 are reserved as well-known port numbers, which are controlled and assigned by the Internet Assigned Numbers Authority (IANA). Only those applications that have been assigned one of these ports should use a number within this range. Refer to the current Assigned Numbers RFC for a list of the port assignments.

Because this range of port numbers, 0-1023, is reserved for the well-known ports, they should not be used by user application programs because it could affect the operation of TCP/IP. For example, restricting the use of ports 21, 23, or 25, prevents other users from using FTP, TELNET, or SMTP, respectively.

The iSeries Add TCP/IP Port Restriction (ADDTCPPORT) command allows you to restrict usage of a single port or a range of ports to a particular iSeries user profile.

Restricting ports is like allocating ports to a specific user profile. When a socket application issues the bind() system call, or when a TCP/UDP Pascal API application issues a call to the TcpOpen, TcpWaitOpen, or UdpOpen function, the job’s user profile is checked against the list of user profiles that are associated with

62OS/400 TCP/IP Configuration and Reference V5R1