Dell Broadcom NetXtreme Family of Adapters - Manual (Page 79)

Broadcom Gigabit Ethernet Teaming Services: Broadcom NetXtreme BCM57XX User Guide
file:///C|/Users/Nalina_N_S/Documents/NetXtreme/English/teamsvcs.htm[9/5/2014 3:32:13 PM]
each team member has been configured similarly. Settings to check include VLANs and QoS Packet Tagging, Jumbo Frames,
and the various offloads. The advanced adapter properties and teaming support are listed in
Table 8 .
Table 8. Advanced Adapter Properties and Teaming Support
Adapter Property Supported by Teamed Virtual Adapter
Checksum Offload Yes
IEEE 802.1p QoS Tagging No
Large Send Offload
Yesa
Jumbo Frames Yes
b
IEEE 802.1Q VLANs Yes
Wake on LAN No
Preboot Execution environment (PXE) Yesc
a All adapters on the team must support this feature. Some adapters may not support this feature if IPMI is also enabled.
b Must be supported by all adapters in the team.
c As a PXE sever only, not as a client.
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