Extreme Networks ExtremeWare 7.2e, Installation And User Manual

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Jumbo Frames
ExtremeWare 7.2e Installation and User Guide 83
of time it takes to transmit one byte on the link at the specified or negotiated link speed. The configured
Interpacket Gap value has no effect on received packets. The default value is 12. The minimum and
maximum allowed values range between 12 and 1023.
The standard effective Interpacket Gap for Gigabit Ethernet interfaces ranges between 12 and 1023.
Some vendors’ 10 Gigabit Ethernet interfaces drop packets when packets are transmitted using a value
of 12. Thus, by increasing the Interpacket Gap, packet transmission is slowed and packet loss can be
minimized or prevented. The Interpacket Gap value need not be modified when interconnecting
Extreme Networks switches over 10 Gigabit Ethernet links. Use the following command to modify the
Interpacket Gap:
configure port <port> interpacket-gap <byte_time>
Jumbo Frames
Jumbo frames are Ethernet frames that are larger than 1522 bytes, including four bytes used for the cyclic
redundancy check (CRC). Extreme products support switching and routing of jumbo frames at
wire-speed on all ports.
Jumbo frames are used between endstations that support larger frame sizes for more efficient transfers
of bulk data. Both endstations involved in the transfer must be capable of supporting jumbo frames.
The switch only performs IP fragmentation, or participates in maximum transmission unit (MTU)
negotiation on behalf of devices that support jumbo frames.
Enabling Jumbo Frames
To enable jumbo frame support, enable jumbo frames on the desired ports. To set the maximum jumbo
frame size, use the following command:
configure jumbo-frame size <number>
The jumbo frame size range is 1523 to 9216. This value describes the maximum size of the frame in
transit (on the wire), and includes 4 bytes of CRC plus another 4 bytes if 802.1Q tagging is being used.
Set the MTU size for the VLAN, using the following command:
configure ip-mtu <number> vlan <vlan name>
The IP MTU default is 1500. The range is 1500-9194.
Next, enable support on the physical ports that will carry jumbo frames using the following command:
enable jumbo-frame ports [<portlist> | all]
NOTE
Some network interface cards (NICs) have a configured maximum MTU size that does not include the
additional 4 bytes of CRC. Ensure that the NIC maximum MTU size is at or below the maximum MTU
size configured on the switch. Frames that are larger than the MTU size configured on the switch are
dropped at the ingress port.