To implement the Citrix CloudBridge Connector solution, you connect a datacenter to another datacenter or an external cloud by setting up a tunnel called the CloudBridge Connector tunnel.
To connect a datacenter to another datacenter, you set up a CloudBridge Connector tunnel between two NetScaler appliances, one in each datacenter.
To connect a datacenter to an external cloud (for example, Amazon AWS cloud), you set up a CloudBridge Connector tunnel between a NetScaler appliance in the datacenter and a virtual appliance (VPX) that resides in the Cloud. The remote end point can be a CloudBridge Connector or a NetScaler VPX with platinum license.
The following illustration shows a CloudBridge Connector tunnel set up between a datacenter and an external cloud.
The appliances between which a CloudBridge Connector tunnel is set up are called the end points or peers of the CloudBridge Connector tunnel.
A CloudBridge Connector tunnel uses the following protocols:
The GRE protocol provides a mechanism for encapsulating packets, from a wide variety of network protocols, to be forwarded over another protocol. GRE is used to:
Connect networks running non-IP and non-routable protocols.
Bridge across a wide area network (WAN).
Create a transport tunnel for any type of traffic that needs to be sent unchanged across a different network.
The GRE protocol encapsulates packets by adding a GRE header and a GRE IP header to the packets.
The Internet Protocol security (IPSec) protocol suite secures communication between peers in the CloudBridge Connector tunnel.
In a CloudBridge Connector tunnel, IPSec ensures:
Data origin authentication
Data confidentiality (encryption)
Protection against replay attacks
IPSec uses the transport mode in which the GRE encapsulated packet is encrypted. The encryption is done by the Encapsulating Security Payload (ESP) protocol. The ESP protocol ensures the integrity of the packet by using a HMAC hash function, and ensures confidentiality by using an encryption algorithm. After the packet is encrypted and the HMAC is calculated, an ESP header is generated. The ESP header is inserted after the GRE IP header and, an ESP trailer is inserted at the end of the encrypted payload.
Peers in the CloudBridge Connector tunnel use the Internet Key Exchange version (IKE) protocol (part of the IPSec protocol suite) to negotiate secure communication, as follows:
The two peers mutually authenticate with each other, using one of the following authentication methods:
- Pre-shared key authentication. A text string called a pre-shared key is manually configured on each peer. The pre-shared keys of the peers are matched against each other for authentication. Therefore, for the authentication to be successful, you must configure the same pre-shared key on each of the peers.
- Digital certificates authentication. The initiator (sender) peer signs message interchange data by using its private key, and the other receiver peer uses the sender's public key to verify the signature. Typically, the public key is exchanged in messages containing an X.509v3 certificate. This certificate provides a level of assurance that a peer's identity as represented in the certificate is associated with a particular public key.
The peers then negotiate to reach agreement on:
This agreement upon the security protocol, encryption algorithm and cryptographic keys is called a Security Association (SA). SAs are one-way (simplex). For example, when two peers, CB1 and CB2, are communicating through a Connector tunnel, CB1 has two Security Associations. One SA is used for processing out-bound packets, and the other SA is used for processing inbound packets.
SAs expire after a specified length of time, which is called the lifetime. The two peers use the Internet Key Exchange (IKE) protocol (part of the IPSec protocol suite) to negotiate new cryptographic keys and establish new SAs. The purpose of the limited lifetime is to prevent attackers from cracking a key.
The following table lists some IPSec propeties supported by a NetScaler appliance:
|IKE Authentication Methods
- Pre-shared key authentication
- Digital certificates authentication
- HMAC SHA1
- HMAC SHA256
- HMAC SHA384
- HMAC SHA512
- HMAC MD5