Remove the Guest LAN To remove a Guest LAN from the system, use the CP DETACH LAN command. This command removes the LAN from the System LAN table, disconnects any virtual adapters that were using the LAN, and releases system resources associated with the LAN. Figure 4-25 illustrates the DETACH LAN command. DETACH LAN TSTLAN OWNER SYSTEM LAN SYSTEM TSTLAN is destroyed Ready; Figure 4-25 DETACH LAN command 4.6.10 Configuring Linux to connect to a Guest LAN Now that we have created a z/VM Guest LAN and connected our guest's virtual NIC to that LAN, it can now be used by Linux. Because z/VM creates a virtual network adapter (NIC) that simulates a real OSA-Express or HiperSockets adapter, the configuration Linux for a virtual adapter is the same as it is for a real one. Please refer back to the previous sections of this book that described the configuration of the real adapters: For a type QDIO network adapter, see "Using OSA-Express with Linux" on page 71. For a type HIPERSOCKETS network adapter, see "Using HiperSockets with Linux" on page 87. Recommendations Linux guests connected to a z/VM Guest LAN must communicate with the physical network through a z/VM TCP/IP or Linux router. This adds both latency and increased CPU utilization to the environment. It also means that it is impossible to participate in an external VLAN. We discuss VLANs in 4.7, "Virtual Switch" on page 108. Additional subnetting is required in this environment, because the Linux guests must be on a separate subnet. z/VM Guest LANs might, however, be appropriate in environments where physical network cards are limited, where there is a requirement for multiple Linux guests in the same z/VM LPAR to communicate with one another, and when the network activity of the Linux guests needs to be isolated from the physical network. Given that VSWITCH can also fulfill these functions and does not have any of the drawbacks previously listed, it might be a more appropriate solution for your environment. We recommend that you use VSWITCH running in Layer 2 Switching mode rather than the standard z/VM Guest LAN. Chapter 4. Networking Overview 107