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Cornelis Technical Documentation

7.4.3.4. IPoIB Troubleshooting

7.4.3.4.1. Viewing IPoIB Hardware Addresses

The arp command and /proc/net/arp do not show the full 20-byte IPoIB hardware address even when the IPoIB and hfi1 modules are working.

  • arp shows only six bytes of the address.

  • /proc/net/arp shows only nine bytes of the address.

To view the full 20-byte hardware address, use ip neigh show.

Address Details

The 20-byte IPoIB hardware MAC address is composed of the following (from most significant bit to least significant bit):

  • 1 byte: Reserved (zero)

  • 3 bytes: Unreliable datagram queue pair (UD QP) number assigned to IPoIB on a given endpoint

  • 16 bytes: GID assigned to Port

    The 16-byte GID includes:

    • 8 bytes: Subnet prefix for CN5000 Omni-Path Fabric

    • 8 bytes: Port GUID

Internet Protocol over InfiniBand- This network interface implementation is IP datagrams over the InfiniBand.

Group Identifier - This is a unique identifier assigned to a group of users on a system, allowing them to access files and directories with common permissions.

Globally Unique Identifier - This is a 128-bit text string generated when a unique reference number is needed to identify a component (for example, hardware, software, node) on a computer or network.