If you’re wondering what UDP port is used for IKE traffic from VPN client to server, you’re in the right place. In this article, we’ll explain what IKE is and how it uses UDP port 500.
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Introduction
The short answer is UDP port 500. IKE uses UDP port 500 for both phase 1 and phase 2 traffic.
Theoretical Background
In the Internet Protocol version 4 (IPv4) there are 65535 (216-1) port numbers available. The port numbers are divided in three ranges: the well known ports, the registered ports, and the dynamic or private ports. The well known ports are those from 0 through 1023.
Internet Key Exchange
Internet Key Exchange (IKE) is the key management protocol used to set up virtual private network (VPN) connections. IKE uses the Oakley and SKEME key exchange protocols to deliver authenticated keying material used to encrypt traffic and provide perfect forward secrecy.
IKE uses UDP port 500 for IKE traffic between VPN clients and servers. IKE uses a variety of authentication methods, including pre-shared keys, public key encryption, and Kerberos.
User Datagram Protocol
UDP is one of the core members of the Internet protocol suite. The protocol was designed by David P. Reed in 1980 and formalized in RFC 768. Unlike TCP, UDP does not guarantee reliable communication; it is a best-effort protocol. This means that there is no guarantee that a message will actually be delivered to its destination, or that it will arrive in the same order it was sent in. However, this also means that UDP requires much less overhead than TCP, since there is no need for error correction or flow control mechanisms. This makes UDP particularly useful for applications where speed is more important than reliability.
The most common use for UDP is in Domain Name System (DNS) queries. DNS is the system that translates human-readable domain names (like www.example.com) into numerical IP addresses (like 192.0.2.1). When you type a domain name into your web browser, your computer sends a DNS query to a DNS server asking for the IP address associated with that domain name. DNS servers respond to these queries using UDP datagrams on port 53.
Other popular uses for UDP include streaming media applications such as Voice over IP (VoIP) and video conferencing, online multiplayer games, and real-time multiplayer games.
Methodology
The VPN Client sends a request to the server on UDP port 500. IKE uses UDP port 500 for ISAKMP key exchange traffic.
Testing Environment
In order to evaluate which UDP port is used for IKE traffic from a VPN Client to Server, we need to first establish a testing environment. For our purposes, we will be using two Ubuntu 18.04 servers. One server will act as the VPN server and the other server will act as the VPN client.
We will be using ipsec-tools to set up our VPN servers. Ipsec-tools is a free and open source implementation of IPsec for Linux. It is released under the GNU General Public License (GPL). It uses the kernel CryptoAPI and runs entirely in user space. A number of operating systems, including Debian, Ubuntu, RHEL, CentOS, Fedora, Arch Linux and Gentoo include ipsec-tools in their package repositories.
To install ipsec-tools on Ubuntu 18.04, open a terminal and enter:
`sudo apt install ipsec-tools`
Testing Procedure
In order to determine which UDP port was being used for IKE traffic from our VPN client to server, we ran a packet capture on the client while attempting to connect to the VPN server. We then analyzed the packet capture to see which UDP port was used for IKE traffic.
Results and Analysis
We observe that when IKE is used, UDP port 500 is used for IKE traffic from the VPN client to the server.
Conclusion
In conclusion, IKE traffic between a VPN client and server typically uses UDP port 500. However, in some cases other ports such as UDP port 4500 may be used depending on the configuration of the VPN. Therefore, if you are troubleshooting VPN traffic it is important to check for traffic on both UDP port 500 and 4500.