3Com V6100, User Manual Manual, Page: 326 / 496

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V6100 and V7122 User Guide
Figure 110 IPSec Encryption
IPSec doesn’t function properly if the gateway’s IP address is changed on-the-fly
due to the fact that the crypto hardware can only be configured on reset. Therefore,
reset the gateway after you change its IP address.
IKE
IKE is used to obtain the Security Associations (SA) between peers (the gateway and the
application it’s trying to contact). The SA contains the encryption keys and profile used by the
IPSec to encrypt the IP stream. The IKE table lists the IKE peers with which the gateway
performs the IKE negotiation (up to 20 peers are available).
The IKE negotiation is separated into two phases: main mode and quick mode. The main
mode employs the Diffie-Hellman (DH) protocol to obtain an encryption key (without any prior
keys), and uses a pre-shared key to authenticate the peers. The created channel secures
the messages of the following phase (quick mode) in which the IPSec SA properties are
negotiated.
The IKE negotiation is as follows:
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Main mode (the main mode creates a secured channel for the quick mode)
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SA negotiation – The peers negotiate their capabilities using four (two for the V6100)
proposals. Each proposal includes three parameters: Encryption method,
Authentication protocol and the length of the key created by the DH protocol. The
key’s lifetime is also negotiated in this stage. For detailed information on configuring
the main mode proposals, see
IKE Configuration .
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Key exchange (DH) – The DH protocol is used to create a phase-1 key.
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Authentication – The two peers authenticate one another using the pre-shared key
(configured by the parameter ‘IKEPolicySharedKey’).
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Quick mode (quick mode negotiation is secured by the phase-1 SA)
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SA negotiation – The peers negotiate their capabilities using four proposals (a single
proposal for the V6100). Each proposal includes two parameters: Encryption method
and Authentication protocol. The lifetime is also negotiated in this stage. For detailed
information on configuring the quick mode proposals, see the SPD table under
IPSec
Configuration .
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Key exchange – a symmetrical key is created using the negotiated SA.