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+# VPP L2-GRE over IPsec implementation    {#ipsec_gre_doc}
+
+This is a memo intended to contain documentation of the VPP L2-GRE over IPsec implementation.
+Everything that is not directly obvious should come here.
+
+
+## L2-GRE over IPsec
+GRE encapsulate layer 2 traffic and IPSec encrypt what is encapsulated by GRE. The whole point of L2-GRE over IPSec is to tunnel layer 2 over GRE and IPSec by bridging the physical interface with IPSec-GRE tunnel interface.
+
+There are 2 dedicated nodes for encapsulation:
+* ipsec-gre<n>-tx - add GRE header
+* esp-encrypt - encrypt GRE packet to ESP packet
+
+There are 3 dedicated nodes for decapsulation:
+* ipsec-if-input - match IPSec SA by source IP address and SPI in ESP packet
+* esp-decrypt - decrypt ESP packet
+* ipsec-gre-input - remove GRE header
+
+
+### Configuration
+
+L2-GRE over IPsec support the following CLI configuration command:
+    create ipsec gre tunnel src <addr> dst <addr> local-sa <id> remote-sa <id> [del]
+
+src: tunnel source IPv4 address
+dst: tunnel destination IPv4 address
+local-sa: tunnel local IPSec Security Association
+remote-sa: tunnel remote IPSec Security Association
+del: delete IPSec-GRE tunnel
+
+L2-GRE over IPsec support the following API configuration command:
+    ipsec_gre_add_del_tunnel src <addr> dst <addr> local_sa <sa-id> remote_sa <sa-id> [del]
+
+src: tunnel source IPv4 address
+dst: tunnel destination IPv4 address
+local_sa: tunnel local IPSec Security Association
+remote_sa: tunnel remote IPSec Security Association
+del: delete IPSec-GRE tunnel
+
+
+### Configuration example
+
+Interface GigabitEthernet0/9/0 is in bridge with ipsec-gre0 tunnel interface, interface GigabitEthernet0/8/0 sending encapsulated and encrypted traffic.
+
+Configure IPv4 address on sending interface:
+set int ip address GigabitEthernet0/8/0 192.168.1.1/24
+
+Configure IPSec Security Associations:
+ipsec sa add 10 spi 1001 esp crypto-key 4a506a794f574265564551694d653768 crypto-alg aes-cbc-128 integ-key 4339314b55523947594d6d3547666b45764e6a58 integ-alg sha1-96
+ipsec sa add 20 spi 1000 esp crypto-key 49517065716d6235726c734a4372466c crypto-alg aes-cbc-128 integ-key 307439636a5542735133595835546f68534e4f64 integ-alg sha1-96
+
+Create IPSec-GRE tunnel:
+create ipsec gre tunnel src 192.168.1.1 dst 192.168.1.2 local-sa 10 remote-sa 20
+
+Set interfaces state:
+set int state GigabitEthernet0/8/0 up
+set int state GigabitEthernet0/9/0 up
+set int state ipsec-gre0 up
+
+Bridge physical interface with IPSec-GRE tunnel interface:
+set interface l2 bridge GigabitEthernet0/9/0 1
+set interface l2 bridge ipsec-gre0 1
+
+
+### Operational data
+
+L2-GRE over IPsec support the following CLI show command:
+    show ipsec gre tunnel
+
+L2-GRE over IPsec support the following API dump command:
+    ipsec_gre_tunnel_dump [sw_if_index <nn>]
+
+sw_if_index: software interface index of the IPSec-GRE tunnel interface
+