---
description: IPsec tunnels can now use the standard NAT traversal flow, starting IKE on UDP port 500 and switching to port 4500 after NAT detection.
title: NAT-T support for IKE on UDP port 500
image: https://developers.cloudflare.com/changelog/post/2026-05-11-nat-t-port-500/og.png?v=d3fec56e40afe739
---

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May 11, 2026

## NAT-T support for IKE on UDP port 500

[Cloudflare WAN](https://developers.cloudflare.com/cloudflare-wan/) [Magic Transit](https://developers.cloudflare.com/magic-transit/)

Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/changelog/post/2026-05-11-nat-t-port-500/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

Cloudflare IPsec now supports the standard NAT traversal (NAT-T) flow, where IKE begins on UDP port `500` and switches to UDP port `4500` after NAT is detected.

Previously, devices behind NAT had to be configured to initiate IKE on UDP port `4500` directly. Devices that started on UDP port `500` could not complete the IKE handshake when NAT was in the path. This required custom configuration on devices such as VeloCloud SD-WAN edges, Cisco IOS-XE routers, and Juniper SRX firewalls, and was not possible on every platform.

What changed:

- Devices behind NAT can now initiate IKE on either UDP port `500` or UDP port `4500`.
- Devices that start IKE on UDP port `500` and switch to UDP port `4500` after NAT detection now complete the handshake successfully.
- No configuration change is required on Cloudflare. The change is available for all IPsec tunnels on Cloudflare WAN and Magic Transit.

This change does not affect existing tunnels:

- Tunnels using UDP port `500` with no NAT detected continue to operate as before.
- Tunnels configured to start IKE on UDP port `4500` continue to operate as before.
- NAT detection logic is unchanged.

For configuration details, refer to [GRE and IPsec tunnels](https://developers.cloudflare.com/cloudflare-wan/reference/gre-ipsec-tunnels/).

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