Port Status and Basic Configuration
Jumbo Packets
■ 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 packets, 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 packets
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 packets 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 packets 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
can occur in situations where a non-jumbo VLAN includes some ports that
do not belong to another, jumbo-enabled VLAN and some ports that do
belong to another, jumbo-enabled VLAN. In this case, ports capable of
receiving jumbo packets can forward them to the ports in the VLAN that
do not have jumbo capability.
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