Hello all, I'm trying to determine the overhead differences between V1 TUN and TAP mode, and I'm running into some difficulties.
Using AES-CBC with SHA-256 in TUN mode, I calculate 20 (IP) + 8 (UDP) + 1 (OPCODE) + 32 (HMAC) + 16 (IV) + 4 (PACKET-ID) + 16 (max PADDING) = 97 bytes. This matches the value I get on my tunnel MTU (1403) when I use -link-mtu 1472: 1500-1403 = 97. For TAP mode, I would have expected 14 (without CRC) or 18 (with CRC) additional bytes (is the original CRC encrypted in TAP mode?). If I use -link-mtu 1472 again however, I get a tap MTU of 1371: 1500-1371=129; 32 more than the 97 I had before. Where do I go wrong in my calculations/assumptions? Kind regards, Pieter Hulshoff
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