Egress PE NAT Operation

A.

The given scenario describes the use of egress PE NAT (Network Address Translation) via a single centralized router to provide Internet access to L3 VPN (Layer 3 Virtual Private Network) customers. In this scenario, NAT is used to translate the private IP addresses of the L3 VPN customers to public IP addresses when accessing the Internet.

Let's examine each of the given answers:

A. The NAT table contains a field to identify the inside VRF of a translation.

This statement is true. In the context of MPLS-based VPNs, a VRF (Virtual Routing and Forwarding) instance is used to isolate the routing tables of different VPNs from each other. The egress PE NAT router needs to know which VRF a packet belongs to in order to perform the correct NAT translation. Therefore, the NAT table used by the router to keep track of NAT translations should contain a field to identify the inside VRF of a translation.

B. Multiple address pools are needed for the same L3 VPN because each site has a separate NAT.

This statement is false. In the given scenario, a single centralized router is used for egress PE NAT. Therefore, all L3 VPN sites use the same NAT address pool, and there is no need for multiple address pools for the same L3 VPN.

C. The different L3 VPNs using the Internet access must not have IP overlaps internally.

This statement is true. Since NAT is used to translate private IP addresses to public IP addresses, it is important to ensure that there are no IP address overlaps between the different L3 VPN sites. Otherwise, there may be conflicts in NAT translations, leading to communication issues.

D. Users in different VRFs cannot share the same outside global IP address.

This statement is false. It is possible for users in different VRFs to share the same outside global IP address. The egress PE NAT router can use the same public IP address for different VRFs as long as it keeps track of the translations using the NAT table. The NAT table should contain a field to identify the inside VRF of a translation to ensure that the translations are performed correctly.

In summary, the correct answer is A: The NAT table contains a field to identify the inside VRF of a translation.