4-10
Software Configuration Guide—Release 12.2(25)EW
OL-6696-01
Chapter 4 Configuring Interfaces
Configuring Optional Interface Features
Configuring Jumbo Frame Support
These subsections describe jumbo frame support:
• Ports and Modules that Support Jumbo Frames, page 4-10
• Understanding Jumbo Frame Support, page 4-10
• Configuring MTU Sizes, page 4-12
Ports and Modules that Support Jumbo Frames
The following ports and modules support jumbo frames:
• 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.
Understanding Jumbo Frame Support
These sections describe jumbo frame support:
• Jumbo Frame Support Overview, page 4-10
• Ethernet Ports, page 4-11
• VLAN Interfaces, page 4-11
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.
Note Jumbo frame support does not fragment Layer 2 switched packets.
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.
To Next Page
Loading...
Need help?
General
