The maximum transmission unitize (MTU) IP frame the switch can receive for Layer 2 frames inbound on a port. The switch drops any inbound frames larger than the MTU allowed on the port. Ports operating at a minimum of 10 Mbps on the HP 3500 switches and 1 Gbps on the other switches covered in this guide can accept forward frames of up to 9220 bytes (including four bytes for a VLAN tag) when configured for jumbo traffic. You can enable inbound jumbo frames on a per-VLAN basis. That is, on a VLAN configured for jumbo traffic, all ports belonging to that VLAN and operating at a minimum of 10 Mbps on the HP 3500 switches and 1 Gbps on the other switches covered in this guide allow inbound jumbo frames of up to 9220 bytes.
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HP Switch does not recommend configuring avoice VLAN to accept jumbo frames. Voice VLAN frames are typically small, and allowing a voice VLAN to accept jumbo frame traffic can degrade the voice transmission performance.
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You can configure the default, primary, and/or (if configured) the management VLAN to accept jumbo frames on all ports belonging to the VLAN.
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When the switch applies the default MTU (1522-bytes including 4 bytes for the VLAN tag) to a VLAN, all ports in the VLAN can receive incoming frames of up to 1522 bytes. When the switch applies the jumbo MTU (9220 bytes including 4 bytes for the VLAN tag) to a VLAN, all ports in that VLAN can receive incoming frames of up to 9220 bytes. 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.
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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.)
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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 also increments the switch's "Giant Rx" counter.
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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 comprising 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 want 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:
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.
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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 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 frames can forward them to the ports in the VLAN that do not have jumbo capability, as shown in Forwarding jumbo frames through non-jumbo ports.
Jumbo frames can also be forwarded out non-jumbo ports when the jumbo frames received inbound on a jumbo-enabled VLAN are routed to another, non-jumbo VLAN for outbound transmission on ports that have no memberships in other, jumbo-capable VLANs. Where either of the above scenarios is a possibility, the downstream device must be configured to accept the jumbo traffic. Otherwise, this traffic will be dropped by the downstream device.
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If a switch belongs to a meshed domain, but does not have any VLANs configured to support jumbo traffic, the meshed ports on that switch drop any jumbo frames they receive from other devices. In this regard, if a mesh domain includes any HP 1600M/2400M/2424M/4000M/8000M switches, along with the switches covered in this guide configured to support jumbo traffic, only the switches covered in this guide receive jumbo frames. The other switch models in the mesh will drop such frames. For more information on switch meshing, see the Advanced Traffic Management Guide.
The maximum frame size for jumbos is supported with the following proprietary MIB object:
This is the value of the global max-frame-size supported by the switch. The default value is set to 9216 bytes.
The IP MTU for jumbos is supported with the following proprietary MIB object:
This is the value of the global jumbos IP MTU (or L3 MTU) supported by the switch. The default value is set to 9198 bytes (a value that is 18 bytes less than the largest possible maximum frame size of 9216 bytes.) This object can be used only in switches that support max-frame-size and ip-mtu configuration.
The port may not be operating at a minimum of 10 Mbps on the HP 3500 switches or 1 Gbps on the other switches covered in this guide. Regardless of a port's configuration, if it is actually operating at a speed lower than 10 Mbps for HP 3500 switches or 1 Gbps for the other switches, it drops inbound jumbo frames. For example, if a port is configured for Auto mode (speed-duplex auto), but has negotiated a 7 Mbps speed with the device at the other end of the link, the port cannot receive inbound jumbo frames. To determine the actual operating speed of one or more ports, view the Mode field in the output for the following command:
The switches can transmit outbound jumbo traffic on any port, regardless of whether the port belongs to a jumbo VLAN. In this case, another port in the same VLAN on the switch may be jumbo-enabled through membership in a different, jumbo-enabled VLAN, and may be forwarding jumbo frames received on the jumbo VLAN to non-jumbo ports.