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10-17
Port Status and Basic Configuration
Jumbo Packets
Jumbo Packets
The Maximum Transmission Unit (MTU) is the maximum size IP packet the
switch can receive for Layer 2 packets inbound on a port. The switch drops
any inbound packets larger than the MTU allowed on the port. On ports
operating at 10 Mbps or 100 Mbps, the MTU is fixed at 1522 bytes. However,
ports operating at 1 Gbps or 10 Gbps speeds accept forward packets of up to
9220 bytes (including four bytes for a VLAN tag) when configured for jumbo
traffic. In switches covered in this guide, you can enable inbound jumbo
packets on a per-VLAN basis. That is, on a VLAN configured for jumbo traffic,
all ports belonging to that VLAN and operating at 1 Gbps or 10 Gbps allow
inbound jumbo packets of up to 9220 bytes. (Regardless of the mode config-
ured on a given jumbo-enabled port, if the port is operating at only 10 Mbps
or 100 Mbps, only packets that do not exceed 1522 bytes are allowed inbound
on that port.)
Terminology
Jumbo Packet: An IP packet exceeding 1522 bytes in size. The maximum
Jumbo packet size is 9220 bytes. (This size includes 4 bytes for the VLAN
tag.)
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
packets from external devices.
MTU (Maximum Transmission Unit): This is the maximum-size IP packet
the switch can receive for Layer 2 packets inbound on a port. The switch
allows jumbo packets of up to 9220 bytes.
Standard MTU: An IP packet of 1522 bytes in size. (This size includes 4 bytes
for the VLAN tag.)
Feature Default Menu CLI Web
display VLAN jumbo status n/a — 10-19 —
configure jumbo VLANs Disabled — 10-21 —