Configuring the MTU

Chapter 4 FCIP over IP/MPLS Core

Testing Scenarios and Results

Figure 4-11 Cisco MDS 9216i Connection to GSR MPLS Core

GSR 12410	GSR 12410
Provider Core	Provider Core

GSR 12410

Provider Core

GSR 12410

Gigabit

Serial/DS3/DS1Ethernet/POS/

GSR 12410

	Ethernet/POS/
Gigabit	Serial/DS3/DS1
Gigabit

10.10.10.1

11.11.11.1

132430

Configuring TCP Parameters on CPE (Cisco MDS 9216)

A simple ping command from the Cisco MDS 9000 CLI, provides the RTT between the two IP addresses. RTT is specified as part of the following configuration command. It may be specified in either microseconds (-us suffix) or in milliseconds (-ms suffix).

The following command shows RTT set for 20 milliseconds:

tcp max-bandwidth-mbps XXXX min-available-bandwidth-mbps xxxx round-trip-time-ms 20

The MTU is the maximum payload the Gigabit Ethernet interface will handle. The default MTU for the Gigabit Ethernet interface is 1500, which does not include Ethernet headers and trailers.

The maximum Fibre Channel frame size including headers and trailers is 2148 bytes. Fibre Channel data frames in typical storage applications have a payload of 2048 bytes plus 36 bytes in headers and trailers, leaving a frame size of 2084 bytes. The Cisco MDS 9000 optionally adds two headers to the Fibre Channel frame. The EISL header is an eight-byte field carrying VSAN tagging information that is only added if the FCIP interface is defined as a TE_Port. If the EISL header is present, it is located immediately after the four-byte start-of-frame (SOF) sequence. There is also an optional header (up to 16 bytes) that is reserved for future use.

With the inclusion of EISL and optional headers, the maximum Fibre Channel frame size is 2172 bytes. An FCIP packet over Ethernet includes 94 to 98 bytes of headers, plus a four-byte Ethernet CRC32 trailer. When carrying the maximum size Fibre Channel frame, the maximum Ethernet frame size is 2274 bytes (2172 + 98 + 4 = 2274).

	Data Center High Availability Clusters Design Guide
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