B.2. Instructions for Configuring the CNS HIPPI Interface

The following instructions explain how to configure the CNS HIPPI interface (hip0).

  1. Perform a telnet to the CNS and log in as root.

  2. Cray does not support dynamic Address Resolution Protocol (ARP) for HIPPI connections.

    After running the cns_gen_config command, you must run the cns_config install command to write the configuration. To activate the configuration, you must reboot the CNS.

    Note: (Deferred implementation) Currently, the cns_gen_config command does not have the ability to generate static ARP for HIPPI, so the prompts for this do not occur.

    Until cns_gen_config is capable of generating static ARP for HIPPI, edit the /cray/etc/cns.conf file to set the static ARP entries for HIPPI by adding the ARP entries just prior to the line that contains:


    Each line in the file defines one host on the HIPPI network and must have the following format:

    hip0 hippi IP address or hostname 00:00:I-field

    The first token, hip0, defines the HIPPI interface to which the ARP entry will be applied.

    The second token, hippi, is a constant used for association of this entry to the CNS HIPPI interface.

    The third token is the IP address or host name associated with the Cray mainframe's HIPPI interface or site HIPPI-connected host.

    The fourth token is the I-field that the CNS is to use to route packets through the HIPPI hardware to the indicated Cray mainframe (00:00: prefix is required).

    An example for the site HIPPI-connected host is:

    hip0 hippi crayhost1-hippi    00:00:01:00:00:04
    hip0 hippi crayhost2-hippi    00:00:01:00:00:42

    An example for the CNS HIPPI connected to the Cray mainframe via a HIPPI modem is:

    hip0 hippi crayhost-1    00:00:00:00:00:00

    The host names (crayhost1-hippi and crayhost2-hippi) identify Cray mainframes attached via HIPPI. The I-fields (01:00:00:04, 01:00:00:42, and 00:00:00:00) are used to route packets through the HIPPI hardware when sending packets to the respective Cray mainframe.

    The components that get configured by the cns_gen_config command are described below:

    IPADDR=ip address


    Identifies the name of the physical card in the CNS that will be used to access the HIPPI network.

    IPADDR=IP address 

    Identifies the CNS's IP address on the HIPPI network.


    Identifies the HIPPI network's netmask.


    Identifies the maximum transmission unit (MTU) of the HIPPI network, as viewed from the CNS.

    Note: MTU values larger than 30000 are not supported.


    Indicates that this interface is to be initialized during CNS initialization (during the boot process).


    Indicates that this interface is defined statically.

    Note: The 30000 byte maximum transmission unit (MTU) does not require changes to the MTU chosen for use by the Cray mainframe. However, all UDP applications (for example, NFS) that will use the CNS as their gateway must be configured to use a message size of 30000 bytes or less. These applications can still use up to the Cray mainframe's HIPPI MTU value when going Cray mainframe to Cray mainframe over HIPPI.

    The MTU on the hip0 interface is set to 30000, as this appears to provide the best throughput to the Cray mainframe going through the CNS.

    The 30000 byte MTU is the only supported value. It was chosen based on the results obtained during performance testing where the MTU was varied between 16K and 64K.

  3. Initialize the CNS HIPPI interface.

    Execute the following command:

    ifup hip0

    Note: The definition of the CNS's own I-field in the static-arp file might produce an error message, because loopback over the physical HIPPI interface is not available. The error message indicates that the I-field definition is not a valid MAC address for the loopback interface.

B.2.1. Configuration Requirements for the Cray Mainframe for GigaRing Systems

The Cray GigaRing mainframe HIPPI arp file (/etc/ghippi.arp) must be updated to include the mapping of the CNS host name to its associated I-field. This is required for the Cray mainframe to correctly route IP packets, which are destined for the CNS HIPPI IP address through the HIPPI network.

For information about how to update the Cray mainframe's HIPPI arp file, see UNICOS Networking Facilities Administrator's Guide or UNICOS/mk Networking Facilities Administration, depending on your operating system.