Understanding IPsec

What IPsec is

IPsec is a security protocol suite that protects data from unauthorized disclosure when it is being transmitted between filers and clients. Using IPsec, you can add policies on the filer that do both of these things:

Configure encryption and authentication algorithms between the filer and client
Policies can be configured from the filer to the client and from the client to the filer over a range of IP addresses and ports.
Negotiate a security association (SA), between the two end-stations (systems that initiate and receive secure communications), that is used for secure data exchanges between the filer and the client
Note
Maintaining security is processor intensive. However, filer security processing can be offloaded from the CPU to an IPsec accelerator adapter. For more information, see Using IPsec hardware acceleration.

About security associations

A security association (SA) is an authenticated simplex (uni-directional) data connection between two end-stations. Security configurations are typically configured in pairs. An SA has all of the following:

A unique Security Parameter Index (SPI) number
An IP destination address
An IPsec security protocol
The IPsec security protocol must be either of the following:
- Authentication Header (AH)
  The AH protocol inserts an authentication header into each packet before the data payload. The authentication header includes a checksum created with a cryptographic hash algorithm, either Message Digest function 95 (MD5 - 128 bit key) or Secure Hash Algorithm (SHA - 160 bit key). The AH protocol does not alter the packet's data payload.
- Encapsulating Security Payload (ESP)
  The ESP protocol inserts a header before the data payload and a trailer after it. When you specify an encryption algorithm, either Data Encryption Standard (DES) or triple DES, ESP alters the data payload by encrypting it. Alternatively, you can specify packet authentication using the same MD5 or SHA-1 algorithms that are available with the AH protocol. If you use the ESP security protocol, you need to specify either authentication or encryption, or both.
  
  Note
  When you specify the AH protocol, only packet authentication (providing data integrity) is enabled. When you specify the ESP protocol, both packet authentication and packet encryption (providing data privacy) can be enabled.

At least two security associations, inbound and outbound, are required between end-stations. Security associations are stored in the Security Association Database (SAD) when IPsec is enabled on an end-station.

Security associations are created from security policies.

About security policies

Security associations are created based on information collected in security policies, which determine how security is handled in a transfer of information. Security policies can include any of the following types of specifications:

The source and destination addresses (or ranges of addresses) of the end-stations (filer and client)
Packet authentication methods
Packet encryption methods
Restrictions on ports and services
Whether inbound and outbound SAs are mirrored
Strictness of policy application

Security policies are stored in the Security Policy Database (SPD) when IPsec is enabled on an end-station. Matching security policies must be configured on the filer and clients.

About key exchange

An IPsec security association (SA) is negotiated by means of the key management protocol IKE (Internet Key Exchange). Phase 1 of an IKE key exchange authenticates the identity of the end-stations, which allows the establishment of an IPsec SA in Phase 2.

Two key exchange mechanisms using IKE are supported between filers and clients: Kerberos and preshared keys.

Kerberos is a network authentication system in which end-stations prove their identity by obtaining identical secret keys from a Key Distribution Center (KDC), the Kerberos security server. For Windows 2000 and later, the KDC is located on the Windows domain controller, which processes IKE authentication requests for filers and Windows clients in the domain.
Kerberos authentication is enabled automatically when CIFS is licensed and configured on a filer.
Preshared keys are identical ASCII text strings entered manually on each end-station. Authentication is validated when IKE successfully compares the hash value of the two keys. Preshared key configuration is simple, but it requires manual management on each end-station. Also, preshared keys are static and persistent, therefore vulnerable unless changed frequently.
Note
The authentication of end-station identity provided by the key exchange protocol IKE is different from the packet integrity authentication provided by the IPsec protocols AH and ESP.

About the Network Appliance IPsec implementation

The IPsec implementation for Network Appliance filers conforms to the Internet Engineering Task Force (IETF) Security Architecture for the Internet Protocol (RFC2401) and related protocols. The following restrictions apply:

By default, filers obey all IPsec parameters that are configured on clients.
The only exception is Perfect Forward Secrecy (PFS), which is not supported on filers.
Only transport mode is supported on filers; tunnel mode is not supported.
Consequently, IPsec is supported for security associations between filers and clients, but it is not supported for security associations between filers and security gateways.
Only clients running Windows 2000 or greater are supported for IPsec connections.
Kerberos authentication is available only for Windows Domains, not Windows Workgroups.

For more information about implementation and standards, see the NetApp ipsec(1) manual page.

IPsec in a cluster configuration

The IPsec protocol, by its nature, does not work well in a failover environment -- where one filer in a cluster configuration must take over the other filer. This is because security policies, but not security associations, are taken over from the failed filer. Clients will continue to send packets to the failed client for the remainder of the client security association lifetime, after which a new security association must be renegotiated and dropped packets resent.

For this reason, Network Appliance recommends that you reduce the security association lifetime to a minimum value to optimize IPsec operation in a cluster configuration. This minimizes the time clients use to destroy their security associations and negotiate new ones with the filer that took over.

Note
You set the value of the security association's lifetime on clients rather than on the filer.

IPsec in a vFiler configuration

IPsec can be enabled on a per-vFiler basis, with distinct security policies for each vFiler. IPsec configuration is preserved when vFilers are moved from one hosting filer to another, unless the vFiler's IP address is changed.

IPsec configuration can be set within the context of a vFiler or at the filer command line by using the vfiler run command.

Note
Policies and configurations discussed in this chapter must be set individually for each vFiler.