iSCSI network

This physical network connects Ethernet iSCSI adapters in the hosting i5/OS™ with Ethernet iSCSI adapters in the hosted system. It is typically a simple, switched, Gigabit Ethernet network. Two kinds of traffic flow over this connection: storage (SCSI) and virtual Ethernet (LAN).

On one side of the network is an iSCSI adapter or adapters controlled by i5/OS. Each iSCSI adapter has two IP addresses: one for SCSI and one for LAN. You configure the IP addresses and other attributes of an adapter in an i5/OS device description object known as the network server host adapter. For more information, see Network server host adapters. Each iSCSI adapter controlled by i5/OS needs its own object. Every iSCSI adapter contains a TCP/IP stack implemented in hardware that is independent of the normal i5/OS TCP/IP stack. When you vary on a network server host adapter, an iSCSI adapter controlled by i5/OS uses the configured values. If you want different values to take effect, you must change the configuration and vary on the server host adapter again. The i5/OS TCP/IP stack is unaware of the IP addresses configured for the iSCSI adapters.

On the other side of the network is an iSCSI adapter or adapters for the hosted system. You configure the IP addresses and other attributes of these adapters in an i5/OS object known as the remote system configuration. For more information, see Remote system configuration. This configuration differs from the i5/OS network server adapter object in several ways:

• You can configure an iSCSI adapter port in a hosted system with 1 or 2 IP addresses: SCSI, LAN, or both. There must be at least one SCSI and one LAN IP address among all of the configured adapters.
• Whenever you configure an IP address for an iSCSI adapter in a hosted system, you must also configure the corresponding adapter MAC address. Each adapter has a label that shows its MAC addresses. Be careful to configure MAC addresses correctly.
• You configure all of the iSCSI adapters for a hosted system in the same i5/OS remote system configuration object. When the integrated server is subsequently varied on, the product automatically ensures that iSCSI adapters in the hosted system are using values in the i5/OS remote system configuration. If you want different values to take effect, you must change the configuration and vary on the server again.
• SCSI traffic uses the iSCSI adapter's hardware TCP/IP stack, but LAN traffic uses the Windows TCP/IP stack. Consequently, the Windows TCP/IP stack is unaware of the SCSI IP address, but is aware of the LAN IP address.

1. In i5/OS configuration objects, network interface information is labeled as local or remote. These terms are relative to i5/OS. Local interface information is for the i5/OS side. Remote interface information is for the Windows hosted system side.
2. The network server host adapter and the remote system configuration define IP address information for opposite sides of the iSCSI network. When connected by a simple, switched network, the following rules apply:
   • The SCSI internet addresses in these two objects that are connected by a switch must be in the same subnet. For example, with IP addresses of the form a.b.x.y and 255.255.255.0 subnet masks, a.b.x must be the same value for both objects.
   • The LAN internet addresses in these two objects that are connected by a switch must be in the same subnet.
   • In the network server host adapter, the gateway elements can be any unassigned IP address in any subnet if you don't have a gateway in your network.
   • In the remote system configuration, the gateway elements should be blank if you don't have a gateway in your network.

DHCP and DHCP relay
There are several methods for delivering boot information to the hosted system. The default method of delivering IP and storage information to boot Windows uses an integrated Dynamic Host Configuration Protocol (DHCP) server on i5/OS side of the iSCSI network. Even with DHCP, the IP address may be considered static because the DHCP server associates a single IP address with a MAC address. For more information, see Diskless booting over iSCSI.

The integrated DHCP server is designed to coexist with any DHCP servers that might also be on the iSCSI network.

If the iSCSI networks includes routers between the iSeries™ server and the hosted system, and the boot information delivery method is DHCP, then an appropriately configured DHCP relay agent, also known as a BOOTP relay agent, is required in the network.

Performance and maximum transmission unit (MTU)
High bandwidth and low latency is desirable for the iSCSI network. Virtual Ethernet can take advantage of an MTU up to a 9000 byte 'jumbo' frame if the network supports the larger MTU. This improves virtual Ethernet performance.

Managing i5/OS iSCSI adapter utilization
Paths configured in the network server description control what storage traffic, if any, and what virtual Ethernet traffic, if any, can flow over an i5/OS iSCSI adapter. For more information, see Manage iSCSI HBA usage.

Multiple hosted systems can use an i5/OS iSCSI adapter simultaneously if multiple network server descriptions use the same network server host adapter object.

Managing hosted system iSCSI adapter utilization
You can configure an iSCSI adapter in a hosted system with a SCSI IP address, a LAN IP address, or both kinds of IP addresses. The presence of a SCSI IP address enables storage traffic, and the presence of a LAN IP address enables virtual Ethernet traffic. Each Windows virtual Ethernet adapter is normally automatically assigned to a physical iSCSI adapter. There is an option on the advanced properties tab of each virtual Ethernet adapter that allows a particular physical iSCSI adapter to be selected. See Manage iSCSI HBA allocation at the Windows side of the iSCSI network.

IBM® does not support the use of the iSCSI adapter as a general purpose external network connection. For more information on external network connections, see External networks.

Other considerations

• The iSCSI network only uses Internet Protocol version 4.
• The frame format is Ethernet version 2.
• The iSCSI network does not support Network Address Translation.

Security
There are several for securing storage traffic and securing virtual Ethernet traffic. For more information, see Security concepts.