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Chapter 4
FCIP over IP/MPLS Core
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.
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
120
100
Scenario 2—Latency Across the GSR MPLS Core
Figure 4-13
Figure 4-13
OL-12518-01
Full Line Rate is Achieved with Packet Size Larger than 1024
80
60
40
20
0
64
128
shows the average latency with a packet size of 2112.
Average Latency—Packet size 2112
1400
1200
1000
800
600
400
200
0
10
20
30
Through Put testing
512
1024
2112
Packet size
Average Latency
Packet size 2112
40
50
60
70
Throughput
Data Center High Availability Clusters Design Guide
Testing Scenarios and Results
2148
80
90
100
Figure 4-12
4-25
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