# Encrypted GRE Tunnel with IPSEC **URL:** https://forum.networklessons.com/t/encrypted-gre-tunnel-with-ipsec/999 **Category:** Lessons Discussion **Created:** [December 26, 2016, 5:54pm UTC](https://forum.networklessons.com/t/encrypted-gre-tunnel-with-ipsec/999 "2016-12-26T17:54:10Z") **Posts on this page:** 1 **Showing post:** 92
### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis) #### Post date: [August 2, 2021, 8:57am UTC](https://forum.networklessons.com/t/encrypted-gre-tunnel-with-ipsec/999/92 "2021-08-02T08:57:56Z")
Hello Giovanni Take a look at this Cisco community forum thread that explains this in detail. > **[How Does NAT-T work with IPSec?](https://community.cisco.com/t5/security-knowledge-base/how-does-nat-t-work-with-ipsec/ta-p/3119442)** > >   Introduction: This document describes details on how NAT-T works.     Background:   ESP  encrypts all critical information, encapsulating the entire inner TCP/UDP datagram within an ESP header. ESP is an IP protocol in the... You may also find this post helpful: > [@Cisco ASA Site-to-Site IKEv1 IPsec VPN](https://forum.networklessons.com/t/cisco-asa-site-to-site-ikev1-ipsec-vpn/825/75): > > Hello Jones Can you specify which lesson in particular you are referring to? There are several site to site VPN lessons using the ASA on the site. Let us know and we can answer your question more appropriately. As for NAT-T, IPsec VPN clients can use NAT traversal to allow for ESP (Encapsulating Security Payload) packets traverse NAT. Several protocols within the IPsec framework must be enabled to traverse both firewalls and NAT including IKE, ESP, AH. UDP port 4500 is used for IPsec NAT t… I hope this has been helpful! Laz --- _[View the full topic](https://forum.networklessons.com/t/encrypted-gre-tunnel-with-ipsec/999)._