1. MSS 1500 - 24 = 1476 (Ethernet + GRE)
2. MSS 1500 - 8 = 1492 (PPPoE)
3. MSS 1454 - 40 = 1414 (NTT NGN + PPPoE)
4. MSS 1454 - 40 - 24 = 1390 (NTT NGN + PPPoE + GRE)
5. MSS 1356 - 24 = 1332 (NTT NGN + PPPoE + IPsec(3des, md5-hamc)+ GRE)

NTT NGN + PPPoE

• MTU 1454
• MSS 1414

NTT NGN + PPPoE + IPsec(ESP, Tunnel mode)

• MSS 1356
• 1414 - 1356 = 58
  • = IP(20) + ESP Header(SPI 4 + Seq 4) + IV (8 (3des: Part of Payload Data)) + ESP Footer(8 (Padding 0 ~ 7 + Pad Length 1 + Next Header 1) + SHA1 12(Authentication Data))
  • = 20 + 4 + 4 + 8 + 8 + 12 = 56

Padding Must be times 8

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