IKE was just used to set up a Site-to-Site tunnel between two Security Gateways to...

The correct answer isC. A successful IPsec VPN negotiation produces an IKE Security Association and IPsec Security Associations. The IKE SA is logically bidirectional because it protects the control-plane negotiation between the peers. The IPsec SAs used for actual encrypted data traffic are unidirectional, so a normal two-way VPN tunnel requires two IPsec SAs: one for traffic from Gateway A to Gateway B and one for traffic from Gateway B to Gateway A. Check Point’s VPN guide explains that the result of IKE negotiation is a Security Association and that IKE Phase II/Quick Mode produces the IPsec Security Association used for IPsec traffic. The standard IPsec model requires separate unidirectional SAs for each direction of ESP/AH-protected traffic. Option A reverses the directionality. Option B incorrectly makes IKE unidirectional and IPsec bidirectional. Option D incorrectly doubles the IKE SA and leaves only one unidirectional IPsec SA, which would not support two-way host communication. Reference topic:IPsec and IKE / Security Associations.

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