Routing considerations for the intraensemble data network

The TCP/IP stack does not allow IP forwarding within the intraensemble data network (IEDN) between two OSA-Express for zBX (OSX) interfaces. However, the stack does allow IP forwarding within the IEDN by the sysplex distributor when VIPAROUTE is used. The stack also allows IP forwarding between an OSX interface and a non-OSX interface.

If an external router is attached to the IEDN, dynamic and static routing considerations for OSX interfaces are the same as those considerations for OSD interfaces connected to an external router. However, if no external router is present on that network, see the following guidelines.

Guidelines:

Implement the IEDN as a flat network, meaning that all addresses that are reachable through the IEDN are in the same subnet (or IPv6 prefix) as the IEDN. In this configuration, a single route (static or dynamic) to this subnet enables all addresses on the IEDN to be reached.
Static routing might be appropriate in the following cases:
- The IEDN is implemented as a flat network, in which case a single static route over the OSX interface to the subnet of the IEDN can reach all destinations in the IEDN.
- A z/OS® host will not be routing traffic between external networks and the IEDN, so you do not want to advertise the intraensemble subnet addresses to the external network.
  Tip: If you are using static routing over the IEDN and there are destination IP addresses on the IBM® zEnterprise® BladeCenter Extension (zBX) that are not part of the intraensemble subnet, you must define static routes to those destination IP addresses on the intraensemble network by using OSX interfaces.
Dynamic routing might be appropriate in the following cases:
- You want destinations on the intraensemble subnet to be reachable from outside the ensemble, and therefore want to advertise the IEDN addresses to the external network.
- There are destination IP addresses on the zBX that are not part of the intraensemble subnet, and you do not want to code individual static routes to reach them (for example, if other hosts on the IEDN have VIPA addresses that are not in the intraensemble subnet).