Exam 300-820 topic 1 question 132 discussion

Note - You must enter the FQDN of the Expressway-E, as it is seen from outside the network, as the peer address on the Expressway-C's secure traversal zone. The reason for this is that in static NAT mode, the Expressway-E requests that incoming signaling and media traffic should be sent to its external FQDN, rather than its private name. This also means that the external firewall must allow traffic from the Expressway-C to the Expressway-E's external FQDN. This is known as NAT reflection, and may not be supported by all types of firewalls.

Ol_Mykhailiuk is spot on per the document. This deployment consists of the following elements: • Single subnet DMZ (10.0.10.0/24) with the following interfaces: • Internal interface of firewall A – 10.0.10.1 (192.168.10.63) • External interface of firewall B – 10.0.10.2 • LAN1 interface of Expressway-E – 10.0.10.3 • LAN subnet (10.0.30.0/24) with the following interfaces: • Internal interface of firewall B – 10.0.30.1 • LAN1 interface of Expressway-C – 10.0.30.2 • Network interface of Cisco TMS – 10.0.30.3 A static 1:1 NAT has been configured on firewall A, NATing the public address 64.100.0.10 to the LAN1 address of the Expressway-E. Static NAT mode is enabled for LAN1 on the Expressway-E, with a static NAT address of 64.100.0.10 (203.0.113.5)

So, in this example, firewall A must allow NAT reflection of traffic coming from the Expressway-C that is destined for the external address, that is 64.100.0.10, of the Expressway-E. The traversal zone on the Expressway-C must have 64.100.0.10 as the peer address. https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/expressway/config_guide/X14-0/basic_config/exwy_b_cisco-expressway-e-and-expressway-c-basic-configuration-deployment-guide-x14-0/exwy_m_advanced-networking-deployments.html