Fortinet FortiWAN, Руководство пользователя

Страница: 190 / 311

IPSec IPSec set up
Configurations of IKE Phase 2
After IKE Phase 1 negotiations complete successfully, Phase 2 negotiation begins. Configurations of Phase 2 defines
the parameters that are required to establish the IPSec Security Association. The basic parameters of IKE Phase 2
settings are associated with a Phase 1 configuration for an establishment of IPSec VPN (IPSec SA). This section we
describe the configurations of IKE Phase 2.
Here are the items and information that you need to determine for IKE Phase 2 settings:
The IKE Phase 2 proposals for negotiating security parameters
Similar to Phase 1 negotiations, the purpose of IKE Phase 2 is to negotiate another set of encryption and
authentication algorithms, and the correspondent secret keys, so that the established IPSec SA provides protection to
subsequent IPSec VPN communications.
IKE Phase 2 negotiations determine:
l
Which encryption algorithms may be applied to provide data confidentiality for IP Encapsulating Security Payload
(ESP)
l
Which authentication hash may be used for data integrity, authentication and anti-replay creating in IP
Encapsulating Security Payload (ESP)
l
Whether PFS is applied to generate a secret session key or not
l
Which Diffie-Hellman group (DH Group) will be used to generate a secret session key if PFS is applied
FortiWAN IKE Phase 2 supports multiple proposals of encryption and authentication algorithms. However, a
successful IKE Phase 2 proposal negotiation requires partially matched proposals on the both units. Incompatible IKE
proposals fails the IKE Phase 2 negotiations. Please make sure on this while configuring.
Similar to the processes in Phase 1, two FortiWAN units handle the negotiations of encryption and authentication
algorithms according to their IKE proposals. The only thing that is different from Phase 1 is Perfect Forward Secrecy
(PFS).
Perfect Forward Secrecy (PFS)
By default, the standard IKE Phase 2 derives the secret session key (for IPSec Security Association) based on the
secret session key of ISAKMP Security Association (outcome of Phase 1 negotiations) without additional private
materials. The secret session keys of IPSec SA might become vulnerable (to be recovered) if the keys of ISAKMP SA
are broken or compromised. Perfect Forward Secrecy (PFS) is the option for IKE Phase 2 to force a new Diffie-Hellman
exchange (it implies a new private key material) involved in the calculations of secret session keys, so that they are
unrelated to only the Phase 1 keys (can not be recovered with only the compromised ISAKMP SA secret key).
Therefore, a DH Group has to be specified for a IKE Phase 2 proposal if the PFS is applied to it. Certainly, PFS gives
securer IPSec SA secret key, but more time is spent on the calculations.
Quick mode selector
Quick mode selector is a rule to determine which packet is transferred throuth IPSec VPN, according to the source IP
address, source port, destination IP address, destination port and protocol of a packet. For Tunnel Mode, it usually
implies the hosts (or a network) behind the two FortiWAN units trying to communicate to each other through the IPSec
VPN tunnel established between the two FortiWAN. Make sure the Quick mode selector of one endpoint is
correspondent to the opposite endpoint. A source IP address defined in the selector in one peer must be defined as the
destination IP address of the selector of the opposite peer, and vice versa. FortiWAN supports only Tunnel Routing
190 FortiWAN Handbook
Fortinet Technologies Inc.