In a Cisco SD-Access network where VXLAN is used for encapsulating data packets, what is the minimum MTU setting that devices should be configured with?

Question

Options

• A1492
• B1500
• C1518
• D1550

• A
  8% (2)
• B
  4% (1)
• D
  88% (22)

Explanation

VXLAN MTU in Cisco SD-Access

VXLAN encapsulation adds 50 bytes of overhead (8-byte VXLAN header + 8-byte UDP header + 20-byte outer IP header + 14-byte outer Ethernet header) to the original 1500-byte payload, requiring a minimum MTU of 1550 bytes on network devices to prevent fragmentation and packet drops. Option A (1492) is associated with PPPoE overhead and is far too small for VXLAN traffic. Option B (1500) is the standard Ethernet MTU for unencapsulated traffic, which would cause fragmentation once VXLAN headers are added. Option C (1518) accounts only for the standard Ethernet frame with an 802.1Q VLAN tag (18 bytes), still insufficient for VXLAN's 50-byte overhead.

Memory Tip: Think "1500 + 50 = 1550" - VXLAN wraps the standard 1500-byte frame in a new set of headers totaling 50 bytes, so always add 50 to the baseline MTU. If you remember that VXLAN = "50 extra bytes," you'll never confuse this with other encapsulation overhead values on the exam.

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