ARP
The OSA-Express adapter in QDIO mode responds to Address Resolution Protocol (ARP) requests for all registered IPv4 addresses.
ARP is a TCP/IP protocol that translates 32-bit IPv4 addresses into the corresponding hardware addresses. For example, for an Ethernet device, the hardware addresses are 48-bit Ethernet Media Access Control (MAC) addresses. The mapping of IPv4 addresses to the corresponding hardware addresses is defined in the ARP cache. When it needs to send a packet, a host consults the ARP cache of its network adapter to find the MAC address of the target host.
If there is an entry for the destination IPv4 address, the corresponding MAC address is copied into the MAC header and the packet is added to the appropriate interface's output queue. If the entry is not found, the ARP functions retain the IPv4 packet, and broadcast an ARP request asking the destination host for its MAC address. When a reply is received, the packet is sent to its destination.
- On an OSA-Express adapter in QDIO mode, do not set the NO_ARP flag on the Linux® Ethernet device. The device driver disables the ARP resolution for IPv4. Because the hardware requires no neighbor lookup for IPv4, but neighbor solicitation for IPv6, the NO_ARP flag is not allowed on the Linux Ethernet device.
- On HiperSockets™, which is a full Ethernet offload engine for IPv4 and IPv6 and supports no other traffic, the device driver sets the NO_ARP flag on the Linux Ethernet interface. Do not remove this flag from the interface.