17–QLogic Teaming Services
Teaming and Other Advanced Networking Properties
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Large Send Offload
Large Send Offload (LSO) is a feature provided by QLogic 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 9600
bytes. Though never formally adopted by the IEEE 802.3 Working Group, support
for jumbo frames has been implemented in QLogic 8400/3400 Series adapters.
The ASP 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 ASP 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 and on a single
adapter. Note that VLANs are supported only with homogeneous teaming and not
in a multivendor teaming environment. The ASP intermediate driver supports
VLAN tagging. One or more VLANs may be bound to a single instance of the
intermediate driver.
