z/VM Virtual Networking Hints and Tips - VLAN Configuration Problems

• z/VM TCP/IP stack TCPIP1 is coupled to a VLAN AWARE virtual switch, authorized for VLAN 7 (for example) but cannot PING a second stack TCPIP2 using VLAN 7.

  What's going on?

  Use the QUERY VSWITCH DETAILS command to display the status of the stacks' connections. In this example, both stacks are defined as TRUNK ports. TCPIP1 has included VLAN 7 on its LINK definition, but TCPIP2 has not. Because all outbound traffic for TCPIP1 is automatically tagged with VLAN 7, a PING flowing from TCPIP1 to TCPIP2 is tagged with VLAN 7. However, because TCPIP2 is defined as a TRUNK port but has not defined a Global VLAN ID no automatic tagging happens. The PING response is not delivered to TCPIP1 because the Global VLAN ID says it is interested only in traffic tagged with VLAN 7.

  To reduce complexity and host TCP/IP configuration changes when configuring a Virtual Switch host connection, it is recommended that you do not configure a global VLAN ID for a host that will be connected to a trunk port. Instead, connect the host to an access port and authorize it for the desired VLAN ID.

This document is maintained by:

Mary Ellen Carollo
z/VM Development
maryelln@us.ibm.com