Any network that has greater addressing capability than its adjacent networks must have extended subarea addressing-capable gateway NCPs and gateway SSCPs that are involved in setting up cross-network sessions for high subareas. Specifically, consider the following situations:

• The gateway NCP addressing capability in each network must be at least equal to the largest subarea address in the network, and its subarea address in the network must be within the range supported by the subarea with the lowest addressing capabilities. This restriction applies only for subareas that are using the gateway NCP for cross-network sessions.
• The gateway VTAM® addressing capability must be greater than or equal to the largest subarea address in the network, and its subarea address must be within the range supported by the SSCP with the lowest addressing capabilities. That is, the gateway SSCP must be capable of supporting a CDRM session with any SSCP in the network, and it must be capable of owning the gateway NCPs it is to control.
• To properly support communication between networks where either network contains subareas that support cross-network sessions and that have subarea addresses above the capabilities of any of the other subareas involved in supporting or setting up the cross-network session, the gateway SSCPs in each network must be capable of supporting extended subarea addressing.
• For an extended subarea addressing gateway NCP to successfully send a CONTACT request unit to an adjacent cross-network gateway NCP with a subarea address greater than 255, the link station must be owned by an extended subarea addressing-capable VTAM.