About this tool

Home internet: path MTU 1500 &rarr; set MSS 1460 . The default that just works.
PPPoE DSL: path MTU 1492 &rarr; set MSS 1452 . The classic case: leave it at 1460 and large downloads stall or crawl, because every full-size packet gets chopped in two. This is the number people google at 2am.
VXLAN overlay: inner MTU 1450 &rarr; set MSS 1410 . One real tunnel: the 50-byte VXLAN wrap eats into the payload, so the MSS comes down with it. This is exactly what the calculator below works out for any stack.

Stack GRE, IPsec, VXLAN, MPLS, PPPoE or WireGuard headers and get the exact byte overhead, the TCP MSS to configure, and whether your packets will fragment — in plain English.

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