Defining SNA DLC links

SNA DLC links are point-to-point and require DEVICE and LINK statements in the configuration data set. The DLC link constitutes a separate network, even though it includes only two hosts. To define a link, each host to which the DLC link is attached requires:

A pair of SNA LU0 DEVICE and LINK statements
A HOME statement
A BSDROUTINGPARMS or GATEWAY or BEGINROUTES statement

SNA DLC links are defined in one of two ways:

By unique network or subnetwork numbers, if the hosts to which they connect are not attached to other networks.
By the IP address of the hosts to which they connect, if the hosts are attached to other networks.

You usually have to assign a unique network or subnetwork number to the SNALINK. If the link connects 2 hosts that also have other networks attached to them, the DLC link does not need its own subnetwork number. Figure 1 illustrates how to define an SNA DLC link if the 2 hosts are connected to other networks in the following way:

Host A and Host B are connected by SNA DLC
Host A is also connected to a token ring, 193.1.1
Host B is also connected to a token ring, 193.1.2
Host A’s home address on its token ring is 193.1.1.1
Host B’s home address on its token ring is 193.1.2.1

Figure 1. SNA DLC link

Host A’s hlq.PROFILE.TCPIP could contain:

     DEVICE  LCS1 LCS BA0
     LINK  TR1  IBMTR 0 LCS1
     DEVICE SNALU0 SNAIUCV SNALINK LU000000 SNALINKA
     LINK SNAIUCV1 SAMEHOST  1 SNALU0
     HOME
         193.1.1.1  TR1
         193.1.1.2  SNAIUCV1
 
     GATEWAY
     ;  Network         First hop  Link    Packet size    Subnet mask
         193.1.1.0      =          TR1         2000        0
         193.1.2.0      =          SNAIUCV1    2000        0

Host B’s hlq.PROFILE.TCPIP could contain:

     DEVICE LCS2 LCS BE0
     LINK  TR1 IBMTR 0 LCS2
     DEVICE SNALU0 SNAIUCV SNALINK LU000001 SNALINKA
     LINK SNAIUCV1 SAMEHOST  1 SNALU0
     HOME
         193.1.2.1  TR1
         193.1.2.2  SNAIUCV1
 
     GATEWAY
     ;  Network         First hop  Link    Packet size    Subnet mask
         193.1.2.0      =          TR1         2000        0
         193.1.1.0      =          SNAIUCV1    2000        0

Notes:

The lu_name must be different on each host. In the example, the lu_name for Host A is LU000000. The lu_name for Host B is LU000001.
In the example, the lu_name is the remote or partner LU.

Hosts A and B are addressed by their token-ring home addresses, even if the packets reach them through the SNA DLC link.

If Host B had no other network attached to it, you would have to assign a separate subnetwork number to the SNA DLC link. Even in this case, Host A does not need a separate home address for its SNA link, because it can be addressed by its token-ring home address. Host B’s only home address is the home address for the SNA link.

Note: If you plan to run a network-monitoring protocol that requires each subnet to have its own subnet number, you can assign a separate subnet network number to the DLC link.