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

■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.

■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.)

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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.

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.

■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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