What is the recommended MTU size for a Cisco SD-Access Fabric?

Question

Options

• A1500
• B9100
• C4464
• D17914

• A
  2% (1)
• B
  90% (38)
• C
  5% (2)
• D
  2% (1)

Explanation

MTU Size for Cisco SD-Access Fabric

Cisco SD-Access uses VXLAN encapsulation to overlay traffic across the fabric underlay, which adds additional header overhead (approximately 50-54 bytes) to each packet. To accommodate this encapsulation without fragmenting traffic, Cisco recommends an MTU of 9100 bytes on all underlay interfaces, ensuring jumbo frames are supported end-to-end throughout the fabric infrastructure.

Why the distractors are wrong:

• A (1500) is the standard Ethernet MTU used in traditional networks, but it is too small for SD-Access as it does not account for VXLAN overhead, leading to fragmentation and performance issues.
• C (4464) is associated with Token Ring or legacy FDDI network MTU sizes and has no relevance to SD-Access fabric design.
• D (17914) is related to older IBM Token Ring (16 Mbps) frame sizes and is not applicable to modern SD-Access deployments.

Memory Tip: Think "9100 = SD-Access jumbo frames" - the "9" reminds you it's a jumbo (large) MTU needed for VXLAN tunneling overhead. Any time you see SD-Access or VXLAN fabric questions, jumbo frames (~9100) should immediately come to mind.

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