Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 48)

30 Brocade ICX 6650 Layer 3 Routing Configuration Guide
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Configuring IP parameters – Layer 3 Switches
Brocade(config)# jumbo
Brocade(config)# write memory
Brocade(config)# end
Brocade# 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:
• 10,240 bytes– The maximum for Ethernet II encapsulation
• 10,240 bytes – The maximum for SNAP encapsulation
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.
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.
Brocade(config)# interface ethernet 1/1/5
Brocade(config-if-e10000-1/1/5)# ip mtu 1000
Brocade(config-if-e10000-1/1/5)# write memory
Brocade(config-if-e10000-1/1/5)# end
Brocade# reload
Syntax: [no] ip mtu num
The num parameter 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 10,240
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 10,240 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
Brocade ICX 6650 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.