HP 2910AL - Manual (Page 326)

Port Traffic Controls
Jumbo Frames
■ When the switch applies the default MTU (1522-bytes) to a VLAN, all ports
in the VLAN can receive incoming frames of up to 1522 bytes in length.
When the switch applies the jumbo MTU (9220 bytes) to a VLAN, all ports
in that VLAN can receive incoming frames of up to 9220 bytes in length.
A port receiving frames exceeding the applicable MTU drops such frames,
causing the switch to generate an Event Log message and increment the
“Giant Rx” counter (displayed by
show interfaces < port-list >).
■ The switch allows flow control and jumbo frame capability to co-exist on
a port.
■ The default MTU is 1522 bytes (including 4 bytes for the VLAN tag). The
jumbo MTU is 9220 bytes (including 4 bytes for the VLAN tag).
■ When a port is not a member of any jumbo-enabled VLAN, it drops all
jumbo traffic. If the port is receiving “excessive” inbound jumbo traffic,
the port generates an Event Log message to notify you of this condition.
This same condition generates a Fault-Finder message in the Alert log of
the switch’s web browser interface, and also increments the switch’s
“Giant Rx” counter.
■ If you do not want all ports in a given VLAN to accept jumbo frames, you
can consider creating one or more jumbo VLANs with a membership
comprised of only the ports you want to receive jumbo traffic. Because a
port belonging to one jumbo-enabled VLAN can receive jumbo frames
through any VLAN to which it belongs, this method enables you to include
both jumbo-enabled and non-jumbo ports within the same VLAN. For
example, suppose you wanted to allow inbound jumbo frames only on
ports 6, 7, 12, and 13. However, these ports are spread across VLAN 100
and VLAN 200, and also share these VLANs with other ports you want
excluded from jumbo traffic. A solution is to create a third VLAN with the
sole purpose of enabling jumbo traffic on the desired ports, while leaving
the other ports on the switch disabled for jumbo traffic. That is:
VLAN 100 VLAN 200 VLAN 300
Ports 6-10 11-15 6, 7, 12, and 13
Jumbo- No No Yes
Enabled?
If there are security concerns with grouping the ports as shown for VLAN
300, you can either use source-port filtering to block unwanted traffic
paths or create separate jumbo VLANs, one for ports 6 and 7, and another
for ports 12 and 13.
■ Outbound Jumbo Traffic. Any port operating at 1 Gbps or higher can
transmit outbound jumbo frames through any VLAN, regardless of the
jumbo configuration. The VLAN is not required to be jumbo-enabled, and
the port is not required to belong to any other, jumbo enabled VLANs. This
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