Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 48)

‐ 10,200 bytes - The maximum for Ethernet II encapsulation (Default MTU: 9216)
‐ 10,174 bytes - The maximum for SNAP encapsulation (Default MTU: 9216)
• For ICX 6630, ICX 6630-C12, and ICX 6450 devices
‐ 10,178 bytes - The maximum for Ethernet II encapsulation (Default MTU: 9216)
‐ 10,174 bytes - The maximum for SNAP encapsulation (Default MTU: 9216)
• For other devices
‐ 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 7750, 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 1/5 to 1000, enter the following commands.
device(config)# interface ethernet 1/5
device(config-if-1/5)# ip mtu 1000
device(config-if-1/5)# write memory
device(config-if-1/5)# end
device# 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 10,218 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
FastIron X Series 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.
Changing the router ID
In most configurations, a Layer 3 switch has multiple IP addresses, usually configured on different
interfaces. As a result, a Layer 3 switch identity to other devices varies depending on the interface to
which the other device is attached. Some routing protocols, including Open Shortest Path First (OSPF)
and Border Gateway Protocol version 4 (BGP4), identify a Layer 3 switch by just one of the IP
Changing the router ID
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