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Data Center High Availability Clusters Design Guide
OL-12518-01
Chapter 4 FCIP over IP/MPLS Core
Testing Scenarios and Results
Where sustained Gigabit throughput is not required (for example, over an OC-12 or slower WAN link),
an MTU of 1500 bytes is adequate. Otherwise, use jumbo frames if possible and set the MTU on the
Gigabit Ethernet interface to 2300. Also, set the MTU size on the CPE to 2300 bytes. You also need to
consider VPN and MPLS headers when configuring MTU size across the path. The MTU size needs to
be configured on all routers and switches, including the CPE in the path. The MTU size of 4700 was
configured on all PE and P routers to accommodate VPN and MPLS specific headers.
Selective acknowledgement (SACK) is enabled by default in the FCIP profile and should not be turned
off. SACK enables the TCP receiver to identify to the sender the contiguous TCP blocks that have been
successfully received. The sender can then
selectively
retransmit only the missing blocks.
Figure 4-12
shows the result for the throughput testing of the MTU. A full line rate is achieved with packet sizes
larger than 1024.
Figure 4-12
Full Line Rate is Achieved with Packet Size Larger than 1024
Scenario 2—Latency Across the GSR MPLS Core
Figure 4-13
shows the average latency with a packet size of 2112.
Figure 4-13
Average Latency—Packet size 2112
132431
Through Put testing
0
20
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64
128
512
1024
2112
2148
T
h
rough put
Packet size
132432
0
200
400
600
800
1000
1200
1400
10
20
30
40
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Throughput
u
sec (
lat
en
cy)
Average Latency
Packet size 2112
