Brocade Communications Systems ICX 7250 series, Configuration Manual

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device(config)# end
device# reload
Syntax: [no] jumbo
NOTE
You must save the configuration change and then reload the software to enable jumbo
support.
Changing the MTU on an individual port
By default, the maximum Ethernet MTU sizes are as follows:
• 1500 bytes - The maximum for Ethernet II encapsulation
• 1492 bytes - The maximum for SNAP encapsulation
When jumbo mode is enabled, the maximum Ethernet MTU sizes are as follows:
• 10,218 bytes - The maximum for Ethernet II encapsulation (Default MTU: 9216)
• 10,214 bytes - The maximum for SNAP encapsulation (Default MTU: 9216)
NOTE
If you set the MTU of a port to a value lower than the global MTU and from 576 through 1499, the port fragments the packets.
However, if the port MTU is exactly 1500 and this is larger than the global MTU, the port drops the packets. For ICX 7250, ICX
7450, and ICX 7750 devices, the minimum IPv4 and IPv6 MTU values for both physical and virtual interfaces are 1280.
NOTE
You must save the configuration change and then reload the software to enable jumbo
support.
To change the MTU for interface 1/1/5 to 1000, enter the following commands.
device(config)# interface ethernet 1/1/5
device(config-if-1/1/5)# ip mtu 1000
device(config-if-1/1/5)# write memory
device(config-if-1/1/5)# end
device# reload
Syntax: [no] ip mtu num
The num variable specifies the MTU. Ethernet II packets can hold IP packets from 576 through 1500 bytes long. If jumbo mode is
enabled, Ethernet II packets can hold IP packets up to 10,218 bytes long. Ethernet SNAP packets can hold IP packets from 576
through 1492 bytes long. If jumbo mode is enabled, SNAP packets can hold IP packets up to 10,214 bytes long. The default MTU for
Ethernet II packets is 1500. The default MTU for SNAP packets is 1492.
Path MTU discovery (RFC 1191) support
ICX 7250, ICX 7450, and ICX 7750 devices support the path MTU discovery method described in RFC 1191. When the Brocade
device receives an IP packet that has its Do not Fragment (DF) bit set, and the packet size is greater than the MTU value of the outbound
interface, then the Brocade device returns an ICMP Destination Unreachable message to the source of the packet, with the Code
indicating "fragmentation needed and DF set". The ICMP Destination Unreachable message includes the MTU of the outbound interface.
The source host can use this information to help determine the maximum MTU of a path to a destination.
RFC 1191 is supported on all interfaces.
Configuring IP parameters - Layer 3 switches
Brocade FastIron Layer 3 Routing Configuration Guide
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