JN0-636 Exam Dumps : Security, Professional (JNCIP-SEC)

Proxy ARP is a technique used by routers to answer ARP requests on one network segment on behalf of hosts on another network segment. This is useful in situations where a host on one network segment needs to communicate with a host on another network segment, but the two hosts are not directly connected. In this case, the router acts as a proxy, answering ARP requests on behalf of the other host. In the exhibit, the vSRX device is configured to use a pool of addresses that are in the same subnet as the external interface ge-0/0/0 for source NAT. This means that the vSRX device will translate the source IP address of the internal hosts to one of the addresses in the pool before sending the packets to the external network. However, the external hosts will not know how to reach the NATed addresses, since they are not directly connected to the vSRX device. They will send ARP requests for the NATed addresses, expecting to receive a MAC address from the vSRX device. If proxy ARP is not enabled on the vSRX device, it will not respond to these ARP requests, since it does not have the NATed addresses configured on its interface. The ARP requests will time out and the packets will be dropped by the external hosts or the service provider router. To solve this problem, proxy ARP must be enabled on the vSRX device for the NATed addresses. This will allow the vSRX device to respond to the ARP requests from the external hosts, providing its own MAC address as the destination. The external hosts will then send the packets to the vSRX device, which will reverse the NAT and forward the packets to the internal hosts. References:

• Configuring Proxy ARP (CLI Procedure)
• [SRX] When and how to configure Proxy ARP (https://supportportal.juniper.net/s/article/SRX-Dynamic-VPN-scenario-for-configuring-Proxy-ARP-on-SRX?language=en_US)

• To solve the problem of using the same IPv4 address space as your company, you can identify two neutral IPv4 address spaces for address translation. This will allow you to use the same IPv4 address space as your company without any conflicts. Additionally, you can configure static NAT on the SRX Series devices to ensure that the traffic is properly routed between the two networks.
• Static NAT is a type of network address translation that maps a private IP address to a public IP address on a one-to-one basis. Static NAT is useful when you need to expose a server or device with a private IP address to the Internet or another network with a different IP address range. Static NAT also preserves the original source or destination IP address in the packet header, which can be useful for logging or auditing purposes1.
• Neutral IPv4 address spaces are IP address ranges that are not assigned to any specific organization or entity. They are usually reserved for special purposes, such as private networks, multicast, loopback, or documentation. Neutral IPv4 address spaces can be used for address translation when there is an overlap or conflict between two networks that need to communicate with each other. For example, you can use the 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 address ranges, which are designated for private use, as neutral IPv4 address spaces for address translation2.

References:

• SRX Getting Started - Configure VPN tunnel for site-to-site connectivity
• SRX & J Series Site-to-Site VPN Configurator
• Resolution Guide – SRX - Troubleshoot Static NAT
• RFC 1918 - Address Allocation for Private Internets