Nortel Web OS 10.0, Application Manual

Page: 63 / 482

Web OS 10.0 Application Guide
Chapter 2: VLANs
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212777-A, February 2002
VLANs and Jumbo Frames
To reduce host frame processing overhead, Gigabit network adapters that can handle frame
sizes of 9K and higher (such as the 3COM PCI-X/PCI Gigabit adapters) and Alteon Web
switches, both running operating Web OS version 2.0 or later, can receive and transmit frames
that are far larger than the maximum normal Ethernet frame. By sending one Jumbo frame
instead of myriad smaller frames, the same task is accomplished with less processing.
The switches and the adapter should support Jumbo frame sizes up to 9018 octets. Jumbo
frames can be transmitted and received between Gigabit adapter-enabled hosts through the
switch across any VLAN that has Jumbo frames enabled.
Isolating Jumbo Frame Traffic using VLANs
Jumbo frame traffic must not be used on a VLAN where there is any device that cannot process
frame sizes larger than Ethernet maximum frame size.
Additional VLANs can be configured on the adapters and switches to support non-Jumbo
frame VLANs for servers and workstations that do not support extended frame sizes. End-sta-
tions installed with Jumbo frames-capable Gigabit adapters, and attached to Web switches can
communicate across both the Jumbo frame VLANs and regular frame VLANs at the same
time.
In the example illustrated in Figure 2-7 on page 64 , the two servers can handle Jumbo frames
but the two clients cannot; therefore Jumbo frames should only be enabled and used on the
VLAN represented by the solid lines but not for the VLAN with the dashed lines. Jumbo
frames are not supported on ports that are configured for half-duplex mode.