tailieunhanh - firewall policies and vpn configurations 2006 phần 6

bây giờ chúng tôi cần phải sử dụng hai lệnh lớp bản đồ được sử dụng để đặt tên cho bản đồ (tức là, SMTP-THANH TRA-8080) và lệnh phù hợp được sử dụng để xác định cổng, giao thức, và số cổng:Cisco PIX là lắng nghe cho giao thông SMTP trên cổng 8080 và cổng cũng có thể kiểm tra một loạt các cảng: | 230 Chapter 5 Defining a VPN The first exchange in main mode negotiates parameters to protect the IKE initiating side sends a proposal to its counterpart and includes parameters it parameters include one encryption algorithm DES 3DES etc. and one of three authentication algorithms preshared secret RSA public key encryption with Diffie-Hellman exchange group 1 and 2 or public key RSA signature this includes use of certificates . The other peer then selects and accepts a single pair from the offered set. If there is no match or agreement the IKE tunnel cannot be established. The second exchange in main mode performs DH key establishment between peers. It exchanges two values called nonces which are hashes that only the other party can confirms that the message is sent by the same hosts as the previous exchange. The third and last exchange authenticates the peers using the agreed-on methods public keys signatures public key encryption or a preshared secret. This exchange is protected by an encryption method that was selected in the first exchange. RFC 2408 provides more details on the packet format and algorithms used. At the end of the first phase each host has an IKE SA which specifies all parameters for this IKE tunnel the authentication method the encryption and hashing algorithm the Diffie-Hellman group used the lifetime for this IKE SA and the key values. Aggressive mode exchanges only three packets instead of six so it is faster but not as secure. Fewer packets are sent because the first two packets in this exchange include almost everything in one message each host sends a proposed protection set Diffie-Hellman values and authentication values. The third packet is sent only for confirmation and after the IKE SA is already weakness in aggressive mode is that everything is sent in clear text and can be captured. However the only thing the attacker can achieve is to DoS one of the peers because it is not