Which method does Cisco SD-WAN use to avoid fragmentation issues?

Question

Options

• APMTUD is used.
• BTraffic is marked with the DF bit set.
• CJumbo frames are enabled.
• DAccess circuits are configured with 1600 byte MTU settings.

• A
  88% (23)
• B
  8% (2)
• D
  4% (1)

Explanation

Cisco SD-WAN uses Path MTU Discovery (PMTUD) to avoid fragmentation. SD-WAN encapsulates traffic in IPsec/GRE tunnels, which adds overhead and reduces the effective MTU of the payload. PMTUD works by sending probe packets with the Don't Fragment (DF) bit set and listening for ICMP 'fragmentation needed' messages to dynamically determine the maximum packet size that can traverse the path without fragmentation. This allows the SD-WAN fabric to adjust packet sizes end-to-end. Option B is partially correct in that the DF bit is involved, but it is the PMTUD process (not simply setting the DF bit) that solves the fragmentation problem. Option C (jumbo frames) increases MTU on LAN segments but does not address WAN tunnel overhead. Option D (1600-byte MTU on access circuits) is a static workaround, not Cisco's SD-WAN standard mechanism.

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