6-12
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
78-14064-04
Chapter 6 Configuring Interfaces
Configuring Optional Interface Features
Bridged and Routed Traffic Size Check at Egress Gigabit Ethernet and 10 Gigabit Ethernet Ports
Jumbo frame support compares egress traffic size with the global egress LAN port MTU size at egress
Gigabit Ethernet and 10 Gigabit Ethernet LAN ports that have a nondefault MTU size configured. The
port drops traffic that is oversized.
With Release 12.1(13)E and later releases, you can configure the global LAN port MTU size (see the
“Configuring the Global LAN Port MTU Size” section on page 6-14). With earlier releases, the LAN
port MTU size is 9216 bytes and 9216 bytes is the only configurable nondefault MTU size for Layer 2
LAN ports.
Ethernet Ports
These sections describe configuring nondefault MTU sizes on Ethernet ports:
• Ethernet Port Overview, page 6-12
• Layer 3 Ethernet Ports, page 6-12
• Layer 2 Ethernet Ports, page 6-12
Ethernet Port Overview
Configuring a nondefault MTU size on a 10, 10/100, or 100 Mbps Ethernet port limits ingress packets
to the global LAN port MTU size and permits egress traffic of any size larger than 64 bytes.
Configuring a nondefault MTU size on a Gigabit Ethernet port permits ingress packets of any size larger
than 64 bytes and limits egress traffic to the global LAN port MTU size.
Configuring a nondefault MTU size on a 10 Gigabit Ethernet port limits ingress and egress packets to
the global LAN port MTU size.
Configuring a nondefault MTU size on an Ethernet port limits routed traffic to the configured MTU size.
With Release 12.1(11b)E and later releases, you can configure the MTU size on any Ethernet port.
With earlier releases, you can configure the MTU size only on Gigabit Ethernet and 10-Gigabit Ethernet
ports.
Layer 3 Ethernet Ports
On a Layer 3 port, you can configure an MTU size that is different than the global LAN port MTU size.
With Release 12.1(13)E and later releases, you can configure a different MTU size on each Layer 3
Ethernet port.
With earlier releases, you can configure only a single larger-than-default MTU size on the router for
Layer 3 Ethernet ports. When you configure a Layer 3 Ethernet port with a nondefault MTU size, the
router automatically configures all other Layer 3 Ethernet ports and Layer 3 EtherChannels with
nondefault MTU sizes to the newly configured size. Layer 3 Ethernet ports and EtherChannels that have
not been changed from the default are not affected.
Note Traffic through a Layer 3 Ethernet LAN port that is configured with a nondefault MTU size is also
subject to the global LAN port MTU size (see the “Configuring the Global LAN Port MTU Size” section
on page 6-14).
Layer 2 Ethernet Ports
On a Layer 2 port, you can only configure an MTU size that matches the global LAN port MTU size (see
the “Configuring the Global LAN Port MTU Size” section on page 6-14).
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