If you’re wondering what UDP port is used for IKE traffic from VPN clients to servers, you’re in the right place. Keep reading to find out.
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IKE uses UDP port 500 for phase 1 traffic and UDP port 4500 for phase 2 traffic.
The Three Main Components of an IKE-Based VPN
IKE is a key exchange protocol that is used in conjunction with the IPSec security protocol to provide a secure VPN connection. IKE uses a variety of UDP ports for communication between VPN clients and servers. The most common UDP port used for IKE traffic is 500.
The Internet Key Exchange (IKE) Protocol
The Internet Key Exchange (IKE) is a key management protocol used to establish authenticated and secure IPsec VPN tunnels. IKE uses a combination of the Diffie-Hellman key exchange algorithm, symmetric-key cryptography, and digital signatures. IKE runs atop the UDP 500 port, making it aPublic Key Infrastructure (PKI) over Internet Protocol security (IPsec) protocol.
IKE consists of two phases:
Phase 1: In this phase, IKE authenticates and negotiates security policy between two devices. Security policy includes IPsec proposal (which includes encryption and authentication algorithms), Diffie-Hellman group, and SA lifetime.
Phase 2: Also known as Quick Mode or IPSec Phase 2, this phase authenticates and negotiates security parameters for data confidentiality, integrity, and anti-replay services for the duration of the session. Quick mode also renegotiates keys if needed and establishes new SAs if required due to text or paging mode message size limitations.
The Authenticated Header (AH) Protocol
IKE uses a variety of protocols and algorithms to set up a VPN. Some of these are designed for use with IP, while others are specific to IKE. The three main components of an IKE-based VPN are the Internet Security Association and Key Management Protocol (ISAKMP), the Oakley Key Determination Protocol (OKD), and the Authenticated Header (AH) protocol.
The ISAKMP is responsible for setting up and maintaining the security associations (SAs) between the two VPN gateways. SAs are used to protect the data exchanged between the two gateways, and they define the security algorithms and keys that will be used.
OKD is used to managed the shared secret keys that are used by the two gateways to encrypt and decrypt data. It is also responsible for distributing these keys to the gateways.
AH is a security protocol that is used to ensure that data cannot be modified in transit. It does this by calculating a message authentication code (MAC) for each packet of data using a shared secret key. The MAC is then added to the packet header, and when the packet arrives at its destination, the MAC is recalculated and checked against the one in the header. If they match, then it is assumed that the data has not been tampered with.
The Encapsulating Security Payload (ESP) Protocol
The Encapsulating Security Payload (ESP) protocol is the main security protocol used in IKE-based VPNs. It provides confidentiality, integrity, and authentication for the data that is sent between the VPN client and server. ESP uses UDP port 500 for IKE traffic from VPN client to server.
The VPN Client
IKE uses UDP port 500 for traffic from the VPN Client to the Server. This is the default port used by IKE.
The IKE Client
IKE is a security protocol that uses UDP port 500. It is used for VPN connections between a client and server. IKE uses a combination of public key and symmetric key algorithms to ensure the confidentiality, integrity, and authenticity of data exchanged between the two hosts.
The AH Client
IKE uses UDP port 500 for phase 1 traffic and UDP port 4500 for phase 2 traffic. When configuring a client device to connect to an Axcient BRC appliance, the user will need to allow UDP ports 500 and 4500 to pass through any firewalls that may be present.
The ESP Client
ESP clients use UDP port 500 to communicate with an ESP server. UDP port 500 is also used for IKE traffic from VPN client to server.
The VPN Server
The VPN server is the gateway to the internet for VPN clients. It is the VPN server that terminates the VPN connection and assigns IP addresses to VPN clients. The VPN server uses UDP port 500 for IKE traffic from the VPN client to server.
The IKE Server
The Internet Key Exchange (IKE) server is responsible for handling all IKE traffic from VPN clients to the VPN server. The IKE server uses UDP port 500 for IKE traffic.
The AH Server
The AH server uses UDP port 500 to communicate with the VPN client.
The ESP Server
UDP port 500 is used for IKE traffic from the VPN server to the VPN client. This is the default port used by the IKE daemon.
After completing this article, you should have a better understanding of what UDP port is used for IKE traffic from VPN client to server, and how to configure your firewall to allow this traffic.