Security, Professional (JNCIP-SEC): JN0-637

Correct Answer: BD

Persistent NAT with target-host restricts session initiation to specific addresses, enhancing security. Reflexive NAT supports multiple connections by preserving the original port. Refer to Juniper NAT Configuration Documentation.

Referring to the NAT configuration shown in the exhibit:

Specific Host Can Initiate a Session (Answer B): The configuration uses persistent NAT with the permit target-host-port statement. This allows a specific external host (based on the target host and port used in the initial session) to initiate a

session back to the internal host after the initial session has been established.

Persistent NAT ensures that the translation state is maintained, allowing external hosts to connect back only under specific conditions (e.g., the same target host and port as used in the original connection). Original Destination Port (Answer

D): The original destination port used by the internal host is retained as the source port when the session is established from outside to inside. This behavior is a result of how persistent NAT binds the internal and external sessions, ensuring

that communication occurs over the same port used for the initial session.

Correct Answer: AC

ADVPN allows on-demand creation of direct spoke-to-spoke VPN tunnels, effectively enabling a full-mesh topology. OSPF is typically used as the routing protocol for these dynamic connections, as it supports dynamic neighbor discovery and

can quickly adapt to topology changes. See Juniper ADVPN Overview.

ADVPN (Auto-Discovery VPN) simplifies the setup of a dynamic VPN for enterprise environments:

Full Mesh Topology (Answer A): ADVPN dynamically establishes direct, on-demand tunnels between sites (spokes) when required, creating a full-mesh topology without the need for predefined static tunnels. This reduces overhead in huband-spoke topologies by bypassing the hub for inter-spoke traffic.

OSPF Routing (Answer C): For ADVPN to function, OSPF (Open Shortest Path First) is commonly used as the dynamic routing protocol to advertise routes between the hub and spokes. OSPF ensures that routes are properly propagated for

dynamic tunnel creation.

OSPF distributes the necessary routing information, enabling the automatic discovery and setup of VPN tunnels between spokes.

Correct Answer: C

DNS doctoring modifies DNS responses for hosts behind NAT devices, allowing them to receive the correct public IP address for internal resources when queried from the public network. This prevents issues where private IPs are returned

and are not reachable externally. For details, visit Juniper DNS Doctoring Documentation.

In this scenario, Host A is trying to resolve the domain name web.acme.com , but the DNS resolution returns the private IP address of the web server instead of its public IP. This is a common issue in networks where private addresses are

used internally, but public addresses are required for external clients.

of Answer C (DNS Doctoring):

DNS doctoringis a feature that modifies DNS replies as they pass through the SRX device. In this case, DNS doctoring can be used to replace the private IP address returned in the DNS response with the correct public IP address for Host A.

This allows external clients to reach internal resources without being aware of their private IP addresses.

Configuration Example:

bash

Copy code

set security nat dns-doctoring from-zone untrust to-zone trust

Juniper Security Reference:

DNS Doctoring Overview: DNS doctoring is used to modify DNS responses so that external clients can access internal resources using public IP addresses. Reference: Juniper DNS Doctoring Documentation.