Data Center Fabric Manager Enterprise User Manual v10.3.X (53-1001357-01, November 2009)

368 DCFM Enterprise User Manual

53-1001357-01

Adaptive Rate Limiting and QoS priorities

Each FCIP circuit is assigned four TCP connections for managing FC Quality of Service (QoS)

priorities over an FCIP tunnel. The priorities are as follows:

• F class - F class is the highest priority, and is assigned bandwidth as needed, at the expense of

lower priorities, if necessary.

• QoS high - The QoS high priority gets at least 50% of the bandwidth.

• QoS medium - The QoS medium priority gets at least 30% of the bandwidth.

• QoS low - The QoS low priority gets at least 20% of the bandwidth.

Adaptive Rate Limiting (ARL) allows you to dynamically adjust bandwidth across priorities so that a

single QoS priority may consume the entire bandwidth when no other QoS priority is in use. ARL

applies a minimum and maximum traffic rate on a circuit, and allows the traffic demand and WAN

connection quality to dynamically determine the rate. As traffic increases, the rate grows towards

the maximum rate, and if traffic subsides, the rate reduces towards the minimum. If traffic is

flowing error-free over the WAN, the rate grows towards the maximum rate. If TCP reports an

increase in retransmissions, the rate reduces towards the minimum.

FCIP Trunk design considerations

There are three basic points to consider when designing an FCIP trunk:

• Each FCIP circuit is assigned a pair of IP addresses, one source IP address, and one

destination IP address.

• The source IP address is used to determine which GbE interface to use. The GbE IP address

must be on the same IP subnet as the source IP address. IP subnets cannot span across the

GbE interfaces.

• The destination IP address is used to determine routing. If the destination IP address is also on

the same subnet as the GbE interface, packets are routed over that subnet. If the destination

IP address is on a different subnet, it must be routed to an IP gateway address.