Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 114)

• On FCX devices, only eight different MTU values can be configured over the whole system. When
the SX-FI48GPP module is installed in the FastIron SX device, the maximum number of different
MTU values that can be configured is 16.
• On both FCX devices, and the SX-FI-24GPP, SX-FI48GPP, SX-FI-24HF, SX-FI-2XG, and SX-
FI-8XG modules, PMTUD will not be enabled on the device if the maximum number of MTU values
has already been configured in the system.
‐ When a new PMTUD value is discovered, and the maximum number of different MTU
values for the system is already configured , the new value will search for the nearest, but
smallest MTU value relative to its own value in the system. For example, in a FCX system,
the new PMTUD value is 800, and the eight different MTU values configured in the system
are 600, 700, 820, 1000, 1100, 1200, 1300, and 1500. The range of MTU values that can
be configured is from 576 through 1500. The new PMTUD value 800 cannot be added to
the system so the nearest, but smallest MTU value is used. In this example, the MTU
value of 700 is considered as the nearest MTU value already configured in the system.
‐ When the new PMTUD value is smaller than all of the eight MTU values configured in the
system, the PMTUD feature is disabled for the tunnel, and the value is not added to the
system. For example, the new PMTUD value is 620 which is smaller in value than all of the
eight, different MTU path values configured in the system. The following warning message
is displayed on the CLI:
Warning - All MTU profiles us
ed, disabling PMTU for tunnel
tunnel_id
; new PMTU was
new pmtu discovered
Tunnel loopback ports for GRE tunnels
For SX-FI624C, SX-FI624P, SX-FI624HF, and SX-FI62XG modules a physical tunnel loopback port is
required for routing a decapsulated packet. When a GRE-encapsulated packet is received on a tunnel
interface, and the packet needs to be decapsulated, the packet is decapsulated and sent to the tunnel
loopback port. The packet is then looped back and forwarded based on the payload packets.
If a tunnel loopback port is not configured, tunnel termination is performed by the CPU. Each GRE
tunnel interface can have one assigned tunnel loopback port and the same tunnel loopback port can
be used for multiple tunnels.
Tunnel loopback ports for GRE tunnels are supported on:
• untagged ports
• ports that are enabled by default
• 10 Gbps and 1 Gbps copper and fiber ports
Note the following hardware limitations for these port types:
• On 10 Gbps ports, the port LEDs will be ON (green) when the ports are configured as tunnel
loopback ports for GRE tunnels. Also, the LEDs will blink when data packets are forwarded.
• On 1 Gbps fiber and copper ports, port LEDs will not be ON when the ports are configured as tunnel
loopback ports for GRE tunnels, nor will the LEDs blink when data packets are forwarded.
Tunnel loopback ports for GRE tunnels are not applicable on:
• tagged ports
• trunk ports
• ports that are members of a VE
• ports that are disabled
• ports that have an IP address
• flow control
• the SX-FI48GPP module
Tunnel loopback ports for GRE tunnels
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