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300-730 · Question #178

Refer to the exhibit. An engineer must configure a FlexVPN site-to-site GRE tunnel that uses IPsec between two Cisco routers. The indicated configuration was applied on Router_B, but the tunnel…

The correct answer is A. 192.16.1.1. In a FlexVPN GRE over IPsec configuration, Router_B must use Router_A's public IP as the tunnel destination so that IKE negotiation can reach the correct peer and the tunnel can be established.

Troubleshooting VPNs

Question

Refer to the exhibit. An engineer must configure a FlexVPN site-to-site GRE tunnel that uses IPsec between two Cisco routers. The indicated configuration was applied on Router_B, but the tunnel fails to come up. Which IP address must be set on Router_B to resolve the issue?

Options

  • A192.16.1.1
  • B192.16.1.2
  • C192.168.10.1
  • D192.168.10.2

How the community answered

(32 responses)
  • A
    75% (24)
  • B
    3% (1)
  • C
    13% (4)
  • D
    9% (3)

Why each option

In a FlexVPN GRE over IPsec configuration, Router_B must use Router_A's public IP as the tunnel destination so that IKE negotiation can reach the correct peer and the tunnel can be established.

A192.16.1.1Correct

Router_B's tunnel destination must reference Router_A's public-facing IP (192.16.1.1) so that GRE-encapsulated packets are directed to the correct peer; without this, IKE cannot initiate Phase 1 with the remote router and the tunnel remains down.

B192.16.1.2

192.16.1.2 is Router_B's own public interface address, so using it as the tunnel destination would loop traffic back to itself rather than reaching Router_A.

C192.168.10.1

192.168.10.1 is a tunnel interface IP used for overlay addressing, not a routable physical destination required for IPsec peer negotiation.

D192.168.10.2

192.168.10.2 is another tunnel interface IP and cannot serve as the physical IPsec peer destination needed for IKE to establish the tunnel.

Concept tested: FlexVPN GRE over IPsec tunnel destination configuration

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_ike2vpn/configuration/xe-16/sec-ike2-vpn-xe-16-book/sec-cfg-flex-vpn.html

Topics

#FlexVPN#GRE tunnel#IP addressing#site-to-site

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