Configuring Jumbo Frame Support - Cisco 4500M Software Manual

Configuring Optional Interface Features

Configuring Jumbo Frame Support

These subsections describe jumbo frame support:
•
•
•
Ports and Modules that Support Jumbo Frames
The following ports and modules support jumbo frames:
•
•
•
•
•
Understanding Jumbo Frame Support
These sections describe jumbo frame support:
•
•
•
Jumbo Frame Support Overview
A jumbo frame is a frame larger than the default Ethernet size. Enable jumbo frame support by
configuring a larger-than-default maximum transmission unit (MTU) size on a port or interface.
Catalyst 4500 series switch Ethernet LAN ports configured with a nondefault MTU size accept frames
containing packets with a size between 1500 and 9198 bytes. With a nondefault MTU size configured,
the packet size of ingress frames is checked. If the packet is larger than the configured MTU, it is
dropped.
For traffic that needs to be routed, the MTU of the egress port is checked. If the MTU is smaller than the
packet size, the packet is forwarded to the CPU. If the "do not fragment bit" is not set, it is fragmented.
Otherwise, the packet is dropped.
Jumbo frame support does not fragment Layer 2 switched packets.
Note
The Catalyst 4500 series switch does not compare the packet size with the MTU at the egress port, but
jumbo frames are dropped in ports that do not support them. The frames can be transmitted in ports that
do support jumbo frames, even though the MTU is not configured to jumbo size.
Software Configuration Guide—Release 12.2(25)EW
4-10
Ports and Modules that Support Jumbo Frames, page 4-10
Understanding Jumbo Frame Support, page 4-10
Configuring MTU Sizes, page 4-12
Supervisor uplink ports
WS-X4306-GB: all ports
WS-X4232-GB-RJ: ports 1-2
WS-X4418-GB: ports 1-2
WS-X4412-2GB-TX: ports 13-14
Each of the last three modules has two non-blocking ports that can support jumbo frames. Other
ports are over-subscribed ports and cannot support jumbo frames.
Jumbo Frame Support Overview, page 4-10
Ethernet Ports, page 4-11
VLAN Interfaces, page 4-11
Chapter 4 Configuring Interfaces
OL-6696-01