Which TCP setting is tuned to minimize the risk of fragmentation on a GRE/IP tunnel?

Question

Options

• AMTU
• BWindow size
• CMRU
• DMSS

• A
  3% (1)
• B
  6% (2)
• C
  3% (1)
• D
  88% (28)

Explanation

GRE/IP Tunnel Fragmentation and MSS Clamping

MSS (Maximum Segment Size) is the correct answer because it is a TCP-level setting that defines the largest payload a TCP segment can carry, and it can be deliberately reduced ("clamped") via a router feature called MSS clamping to account for the extra overhead added by GRE and IP encapsulation headers - preventing fragmentation before packets are even sent.

MTU (A) is an interface-level setting, not a TCP setting; while it relates to fragmentation, it is not tuned at the TCP layer to minimize risk in tunnels - the question specifically asks about a TCP setting. Window size (B) controls how much unacknowledged data can be in flight, affecting throughput and flow control, not packet fragmentation. MRU (C) - Maximum Receive Unit - relates to the maximum size a device is willing to receive, and while relevant in PPP contexts, it is not the TCP setting used to combat GRE tunnel fragmentation.

Memory Tip: Think "MSS = My Segment Shrinks" - when a GRE tunnel adds overhead, you shrink the MSS so that the final encapsulated packet still fits within the MTU, avoiding fragmentation entirely.

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