Hi
There are two different subject :
1-Tunneling
2-Encryption
L2TP is a tunneling protocol it means the tunnel use capsulation and encapsulation at the end of the tunnels , and by default data transfer in tunnel in plain mode (not encrypted)
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Hello I am plain text
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in above diagram => ===== means tunnel and "Hello I am plain text" is data
IPSEC
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hkjeu349khjkd344
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in above diagram => ====== means tunnel and "hkjeu349khjkd344" is encrypted data using IPsec
GRE or L2tp made tunnel for us and IPSEC encrypt all data in the tunnel