Network Express virtual MAC routing

Network Express supports layer 2 mode only. All Network Express INTERFACEs require a VMAC address. The Network Express physical burned in MAC address cannot be used. Each protocol being used (IPv4 or IPv6) must use VMAC.

For IPv4, Network Express provides the ARP offload function. This results in the Network Express feature using the VMAC address for all ARPs sent for that TCP/IP stack's registered IP addresses. The TCP/IP stack will use the VMAC as the source MAC address for all unicast packets sent from that stack.

This simplification is true for IPv6 as well. TCP/IP uses the VMAC address for all neighbor discovery address resolution flows for that stack's IP addresses, and likewise uses the VMAC as the source MAC address for all IPv6 packets sent from that stack. Again, from a network perspective, the OSA-Express feature with this VMAC appears as a dedicated device to that stack.

For IPv6, neighbor discovery processing is done in the TCP/IP stack. TCP/IP uses the VMAC address for all neighbor discovery address resolution flows for that stack's IP addresses, and likewise uses the VMAC as the source MAC address for all IPv6 packets sent from that stack.

From a network perspective, the Network Express feature with a VMAC address per INTERFACE appears as a dedicated device to that stack.

In this way, all routers on the same LAN as the Network Express feature use only the VMAC address as the destination for all packets destined for that specific TCP/IP stack. From a network routing perspective, the Network Express feature with this VMAC appears as a dedicated device to the remote TCP/IP stacks.

The Network Express EQDIO architecture significantly simplifies a shared OSA configuration. The routers on the LAN always send any packets destined for a particular TCP/IP stack to the VMAC defined for that stack. The Network Express feature knows by VMAC address exactly which stack should receive a given packet. Even if the IP address is not registered with the OSA-Express feature, if the packet is destined for that VMAC, the router has determined which stack should be the intermediate router (see Route ALL parameter), and the OSA can forward the packet directly to that stack. If the stack is not an intermediate router, the capability is provided for a stack to indicate to the OSA that it wants to receive packets to registered IP addresses only (see Route Local parameter). This simplification is true for IPv6 as well. TCP/IP uses the VMAC address for all neighbor discovery address resolution flows for that stack's IP addresses, and likewise uses the VMAC as the source MAC address for all IPv6 packets sent from that stack.

The VMAC address can be defined in the stack (by the administrator), or it can be generated by the OSA. If generated by the OSA, it is guaranteed to be unique from all other physical MAC addresses and from all other VMAC addresses generated by any Network Express feature.

Rule: When VMACs are defined in the stack by an administrator, they should be defined as locally administered MAC addresses, and should be unique addresses for the associated local LAN.

Requirement: If the OSA is configured for both IPv4 and IPv6 for a stack, then you must define one VMAC on the INTERFACE statement for IPv4 usage, and a different VMAC on the INTERFACE statement for IPv6 usage.

The Network Express feature (EQDIO) does not require user defined VTAM TRLE definitions. EQDIO TRLEs are dynamically built when the EQENET INTERFACEs are started. This design aspect simplifies the planning and administrative tasks associated with Network Express. There are no associated configuration tasks in VTAM for Network Express INTERFACEs and there are no topics in or references to the z/OS Communications Server: SNA Network Implementation Guide. All z/OS configuration planning and guidance associated with Network Express INTERFACEs is contained within this IP Configuration Guide. Users must complete the system I/O configuration steps for OSH and devices (HCD).