12-3
Port Traffic Controls
Jumbo Frames
Jumbo VLAN: A VLAN configured to allow inbound jumbo traffic. All ports
belonging to a jumbo and operating at 1 Gbps or higher can receive jumbo
frames from external devices. If the switch is in a meshed domain, then
all meshed ports (operating at 1 Gbps or higher) on the switch will accept
jumbo traffic from other devices in the mesh.
MTU (Maximum Transmission Unit): This is the maximum-size IP frame
the switch can receive for Layer 2 frames inbound on a port. The switch
allows jumbo frames of up to 9220 bytes. (This size includes 4 bytes for
the VLAN tag.)
Standard MTU: An IP frame of 1522 bytes in size. (This size includes 4 bytes
for the VLAN tag.)
Operating Rules
â– Required Port Speed: This feature allows inbound and outbound jumbo
frames on ports operating at speeds of 1 gigabit or higher. At lower port
speeds, only standard (1522-byte or smaller) frames are allowed, regard-
less of the jumbo configuration.
â– Switch Meshing: If you enable jumbo traffic on a VLAN, then all meshed
ports on the switch will be enabled to support jumbo traffic. (On a given
meshed switch, every meshed port operating at 1 Gbps or higher becomes
a member of every VLAN configured on the switch.)
â– GVRP Operation: A VLAN enabled for jumbo traffic cannot be used to
create a dynamic VLAN. A port belonging to a statically configured, jumbo-
enabled VLAN cannot join a dynamic VLAN.
â– Port Adds and Moves: If you add a port to a VLAN that is already
configured for jumbo traffic, the switch enables that port to receive jumbo
traffic. If you remove a port from a jumbo-enabled VLAN, the switch
disables jumbo traffic capability on the port only if the port is not currently
a member of another jumbo-enabled VLAN. This same operation applies
to port trunks.
â– Jumbo Traffic Sources: A port belonging to a jumbo-enabled VLAN can
receive inbound jumbo frames through any VLAN to which it belongs,
including non-jumbo VLANs. For example, if VLAN 10 (without jumbos
enabled) and VLAN 20 (with jumbos enabled) are both configured on a
switch, and port 1 belongs to both VLANs, then port 1 can receive jumbo
traffic from devices on either VLAN. For a method to allow only some
ports in a VLAN to receive jumbo traffic, refer to “Configuring a Maximum
Frame Size” on page 12-7.
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