Checksum Offload; Large Send Offload; Jumbo Frames; Preboot Execution Environment (Pxe) - Dell Broadcom NetXtreme Family of Adapters User Manual

Checksum Offload

Checksum Offload is a property of the Broadcom network adapters that allows the TCP/IP/UDP checksums for send and
receive traffic to be calculated by the adapter hardware rather than by the host CPU. In high-traffic situations, this can allow
a system to handle more connections more efficiently than if the host CPU were forced to calculate the checksums. This
property is inherently a hardware property and would not benefit from a software-only implementation. An adapter that
supports Checksum Offload advertises this capability to the operating system so that the checksum does not need to be
calculated in the protocol stack; because the intermediate driver is located directly between the protocol layer and the
miniport driver, the protocol layer is not able to offload any checksums. Checksum Offload is only supported for IPv4 at this
time.
IEEE 802.1p QoS Tagging
The IEEE 802.1p standard includes a 3-bit field (supporting a maximum of 8 priority levels), which allows for traffic
prioritization. The BASP intermediate driver does not support IEEE 802.1p QoS tagging.

Large Send Offload

Large Send Offload (LSO) is a feature provided by Broadcom network adapters that prevents an upper level protocol such as
TCP from breaking a large data packet into a series of smaller packets with headers appended to them. The protocol stack
need only generate a single header for a data packet as large as 64 KB, and the adapter hardware breaks the data buffer into
appropriately-sized Ethernet frames with the correctly sequenced header (based on the single header originally provided).

Jumbo Frames

The use of jumbo frames was originally proposed by Alteon Networks, Inc. in 1998 and increased the maximum size of an
Ethernet frame to a maximum size of 9000 bytes. Though never formally adopted by the IEEE 802.3 Working Group, support
for jumbo frames has been implemented in Broadcom adapters. The BASP intermediate driver supports jumbo frames,
provided that all of the physical adapters in the team also support jumbo frames and the same size is set on all adapters in
the team.
IEEE 802.1Q VLANs
In 1998, the IEEE approved the 802.3ac standard, which defines frame format extensions to support Virtual Bridged Local
Area Network tagging on Ethernet networks as specified in the IEEE 802.1Q specification. The VLAN protocol permits insertion
of a tag into an Ethernet frame to identify the VLAN to which a frame belongs. If present, the 4-byte VLAN tag is inserted into
the Ethernet frame between the source MAC address and the length/type field. The first 2-bytes of the VLAN tag consist of
the IEEE 802.1Q tag type, whereas the second 2 bytes include a user priority field and the VLAN identifier (VID). Virtual LANs
(VLANs) allow the user to split the physical LAN into logical subparts. Each defined VLAN behaves as its own separate
network, with its traffic and broadcasts isolated from the others, thus increasing bandwidth efficiency within each logical
group. VLANs also enable the administrator to enforce appropriate security and quality of service (QoS) policies. The BASP
supports the creation of 64 VLANs per team or adapter: 63 tagged and 1 untagged. The operating system and system
resources, however, limit the actual number of VLANs. VLAN support is provided according to IEEE 802.1q and is supported in
a teaming environment as well as on a single adapter. Note that VLANs are supported only with homogeneous teaming and
not in a multivendor teaming environment. The BASP intermediate driver supports VLAN tagging. One or more VLANs may be
bound to a single instance of the intermediate driver.
Wake on LAN
Wake on LAN (WOL) is a feature that allows a system to be awakened from a sleep state by the arrival of a specific packet
over the Ethernet interface. Because a virtual adapter is implemented as a software only device, it lacks the hardware
features to implement Wake on LAN and cannot be enabled to wake the system from a sleeping state via the virtual adapter.
The physical adapters, however, support this property, even when the adapter is part of a team.

Preboot Execution Environment (PXE)

The Preboot Execution Environment (PXE) allows a system to boot from an operating system image over the network. By
definition, PXE is invoked before an operating system is loaded, so there is no opportunity for the BASP intermediate driver to
load and enable a team. As a result, teaming is not supported as a PXE client, though a physical adapter that participates in a
team when the operating system is loaded may be used as a PXE client. Whereas a teamed adapter cannot be used as a PXE
client, it can be used for a PXE server, which provides operating system images to PXE clients using a combination of