关于TCP-MSS的解释
The command set flow all-tcp-mss is used in cases where fragmentation can cause performance problems. This will modify the maximum segment size (MSS) low enough below the Maximum Transmission Unit (MTU) so that fragmentation will not occur. A packet with the payload size plus all associated overhead must not exceed the MTU. Otherwise, fragmentation will occur. Overhead can include mac headers, ethernet headers, CRC, encryption, and PPPoE. The set flow all-tcp-mss applies to clear-text traffic, while set flow tcp-mss applies to VPN traffic only.
The set flow all-tcp-mss is required when using PPPoE, as PPPoE adds considerable overhead, and fragmentation will occur if the set flow all-tcp-mss command is not enabled. There are also some instances where a router may not be handling fragmentation properly. In these instances, set flow all-tcp-mss may help. For example, if accessing a web site, and not all images are drawn, this symptom could be due to fragmentation. Applying the set flow all-tcp-mss can resolve this issue
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