Configuring ATM Networks

This article describes how to configure Linux-based PCs and an asynchronous transfer mode (ATM) switch to build on ATM network.
Using IP over Permanent Virtual Circuits

To establish a PVC, the following steps must be performed.

  • On the workstation, add an ATM ARP entry on each node specifying the PVC (vpi.vci pair) used to connect to each of the other hosts.

  • Create the PVC on the switch.

As an example, the following commands executed on the appropriate host will set up a PVC between nodes named node1 and node2, on interface 0, using a vpi of 0 and a vci of 70:

  • node1: atmarp -s node2 0.0.70

  • node2: atmarp -s node1 0.0.70

The PVC is identified by three numbers, separated by two periods. The numbering scheme is interface.vpi.vci, where interface is 0 for the first ATM adapter, 1 for the next, etc. The default interface for the atmarp command is 0. The vpi (virtual path identifier) and vci (virtual channel identifier) are the standard ATM PVC identifiers. The host name (node1 and node2) can be used if there is an entry for it in the /etc/hosts file; otherwise, use the IP address of the host.

The commands above tell node1 to communicate with node2 over PVC 0.0.70 and for node2 to communicate with node1 over PVC 0.0.70. The atmarp command links the IP address of the target host to the PVC. You could choose a different PVC for each connection, but it is simpler to think in terms of one PVC connecting two machines.

The vpi.vci pair must not be in use on the host. Also, any ATM ARP cache entries must be deleted for the target host before creating the PVC. (These cache entries are created when SVCs are opened to the destination host.) To delete an ARP cache entry on node1 for node2, you would use this command:

node1: atmarp -d node2

Next, the switch must be configured to complete the PVC between the hosts. It is helpful to understand the port naming convention used by the Fore switch. The port names consist of three identifiers:

  • Board: the number of the switch board (same as the SCP number); each SCP controls one switch board.

  • Network Module: the slot (A, B, C, or D) in the switch board containing the port.

  • Port: the physical port number on the network module.

For example, port 1b3 refers to the first switch board, the second network module (module b) on board 1 and the third physical port on the second network module. The Fore ASX-200 switch has only one switch board, while the ASX-1000 switch has four. There is a maximum of four network modules per switch board and a maximum of six physical ports per module.

You must now create the virtual channels on the ATM switch. In our example, you would enter these commands on SCP 1:

localhost::> conf vcc
localhost::configuration vcc> new 1a1 0 70 1a2 0 70
localhost::configuration vcc> new 1a2 0 70 1a1 0 70

1a1 is the switch port for node1 and 1a2 is the switch port for node2.

The switch completes the PVC based on the input port to output port virtual channel connection (VCC) mapping. Note that the PVC vpi.vci (0.70) matches the vpi.vci given to the atmarp commands on the hosts.

The above commands will connect two ports on the same ATM switch board. The Fore ASX-1000 switch has up to four switch boards. If you are connecting machines on different switch boards, the procedure is more complicated, as you must connect each port to the switch fabric and connect the fabric to each port. Thus, if you wish to connect a machine on port 1a1 to a machine on port 3a1, the following commands are required:

On SCP 1:

localhost::> conf vcc
localhost::configuration vcc> new 1a1 0 70 1e3 0 70
localhost::configuration vcc> new 1e3 0 70 1a1 0 70

On SCP 3:

localhost::> conf vcc
localhost::>configuration vcc> new 3a1 0 70 3e1 0 70
localhost::>configuration vcc> new 3e1 0 70 3a1 0 70
On the Fore switch, the fabric connections are slot e. Therefore, port 1e3 refers to a connection from switch board 1 to switch board 3. Likewise, 3e1 refers to a connection from switch board 3 to switch board 1. Fore refers to these ports as “intra-fabric” ports.

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