# Secure GRE Tunnel

###### tags: `cisco` `gre`

Steps for creating secure GRE tunnel in cisco routers.
Following shows the steps and related commands used for each step to configure secure GRE tunel.

---------------------------------------------------
1. configure GRE tunnel
---------------------------------------------------
#interface tunne <number>
#tunnel source <outside interface/IP>
#tunnel destination <remote end IP>
#ip address tunnel <interface IP>


---------------------------------------------------
2. configure IKE policy and pre-shared key
---------------------------------------------------
#crypto isakmp enable
#crypto isakmp policy
#authentication <pre-share | rsa-sig | rsa-encr(pre-share)>
#encryption <des | 3des>
#hash <sha | md5>
#group <1 | 2>
#lifetime <seconds>
#crypto isakmp key <keystring> address <peer-address>


---------------------------------------------------
3. ipsec transform sets (maybe also configure lifetime or leave it as default)
---------------------------------------------------
#crypto ipsec transform-set <xauthransform | reomte> <esp-des> <esp-md5-hmac>
#crypto ipsec secrity-association lifetime seconds <seconds>


---------------------------------------------------
4. define traffic ACL
---------------------------------------------------
#access list <number ID> permit ip <source network IP> <wildcard mask> <destination network IP> <wildcard mask>


---------------------------------------------------
5. create, apply crypto maps
---------------------------------------------------
#crypto map <map name> <sequencial number> ipsec-isakmp
#match address <access list ID>
#set peer <hostname | ip-address>
#set pfs <group1 | group2>
#set transform-set <transform-set-name1 ...transform-set-name#>
#set security-association lifetime second <seconds>

#interface <interface name for apply crypto map(tunnel #)>
#crypto map <map name>