VLAN / QinQ Tag Overhead Calculator

QinQ 802.1Q stacking technical infographic showing outer and inner VLAN tags added to an Ethernet frame, with TPID/TCI breakdown and byte overhead for single-tag and QinQ stacking

See the exact byte cost of stacking 802.1Q/QinQ VLAN tags, and check whether two vendors will actually interoperate before you build a QinQ trunk between them — the outer tag's EtherType (TPID) is the single most common reason a working single-vendor QinQ link breaks the moment it crosses to a different platform.

Tag Stack

Untagged+0 B Single 802.1Q+4 B QinQ (double-tag)+8 B Triple-tag (rare)+12 B

Tag Overhead

0 B

Max Frame Size

1518 B

Tags

VLAN tags are pure L2 overhead — they don't reduce the L3/IP payload on platforms whose mtu is L3-only, but do need to be added to the configured mtu number on platforms where it includes the L2 header. Stacking these tags with a tunnel (GRE/VXLAN/IPsec/etc)? Use the MTU / Encapsulation Overhead Calculator for the full per-platform number.

Configured Interface MTU

bytes (the L3/IP payload you need to preserve end-to-end)

Platform	Set interface mtu to	Why

Vendor QinQ Interop Checker

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All Platforms at a Glance

Platform	Outer TPID when QinQ-configured	What to configure

Sourced from vendor documentation: Cisco IEEE 802.1Q Tunneling config guide, Juniper flexible-vlan-tagging reference, FortiOS QinQ 802.1ad admin guide, Arista dot1q/TPID TOI, and Palo Alto LIVEcommunity threads on QinQ/802.1ad limitations.

Provided as-is, with no warranty of any kind. Exact CLI syntax and default behavior vary by platform family and software version within each vendor (e.g. classic Cisco IOS vs. IOS-XE service-instance config, Junos EX/QFX vs. MX, FortiOS release) — verify against your own gear and current documentation before applying to production. See the full disclaimer.