MTU & Fragmentation Explorer

Model packet size, nested overhead, effective MTU/MSS, and standards-based fragment arithmetic without sending packets.

Arithmetic model only: no packet is created or transmitted. Real paths may use offloads, variable tunnel padding, authentication tags, extension headers, policy minimums, MSS clamping, interface/link MTUs, or encapsulation behavior different from these entered overheads. VLAN/MPLS are shown as user-selected carrier-budget deductions even though operational MTU conventions vary.

Inner packet

IP version

Transport

Application payload bytes

Carrier/path MTU bytes

Per-fragment IP option / extension bytes

TCP option bytes

Custom L4 header bytes

Additional custom encapsulation bytes

Entered IPv4 option bytes are assumed copied into every fragment; entered IPv6 extension bytes are assumed to precede the Fragment header and therefore appear in every fragment packet.

IPv4 Don't Fragment (DF) IPv6 source fragmentation selected IPv6 jumbogram explicitly modeled Assume PMTUD/PLPMTUD is attempted

Nested encapsulation budget

Preset tunnel values are illustrative fixed budgets, not protocol guarantees. Edit the custom overhead to represent actual outer IP versions, options, labels, IVs, padding, tags, or multiple tunnel layers.

Result

Fragment plan

IP packet or fragment sizes and offset fields
Fragment	Offset units	Offset bytes	IP payload portion	IP/fragment headers	Total bytes	MF / more