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300-410 Practice Question: The default MTU size for ERSPAN encapsulated…

What is the default MTU size for ERSPAN encapsulated packets on Cisco IOS-XE?

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The ERSPAN packet inherits the interface MTU, with no separate default.

ERSPAN adds a GRE header (4 bytes) and an ERSPAN header (4 bytes for Type II) to the original packet. The default system MTU is 1500 bytes, but the ERSPAN packet may exceed this; however, the default MTU for the ERSPAN session itself is not explicitly set—it inherits the interface MTU. There is no separate default ERSPAN MTU; the question tests understanding that ERSPAN adds 8 bytes overhead.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    1500 bytes

    Why it's wrong here

    1500 is the typical Ethernet MTU, but ERSPAN adds overhead, so the effective packet size is larger.

  • ✗

    1492 bytes

    Why it's wrong here

    1492 is for PPPoE, not ERSPAN.

  • ✓

    The ERSPAN packet inherits the interface MTU, with no separate default.

    Why this is correct

    ERSPAN does not have a configurable MTU; it uses the interface MTU, and the encapsulation adds 8 bytes (Type II) overhead.

  • ✗

    The default ERSPAN MTU is 1518 bytes.

    Why it's wrong here

    1518 is the maximum Ethernet frame size including header, but ERSPAN can exceed that if the original packet is large.

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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