Question 288 - PCNSE discussion

According to the Palo Alto Networks documentation1, the error message "IKE phase-2 negotiation failed when processing Proxy ID" indicates that there is a mismatch between the Proxy ID settings on the two VPN peers. Proxy ID is used to identify the traffic that needs to be encrypted and tunneled. It consists of the local and remote IP addresses, protocols, and ports. If the Proxy ID settings do not match on both VPN peers, the phase-2 negotiation will fail. Therefore, the administrator should check whether the VPN peer on one end is set up correctly using policy-based VPN, which allows specifying the Proxy ID settings manually2. Therefore, the correct answer is C.

The other options are not relevant or helpful for identifying the root cause of this error message:

In the IKE Gateway configuration, verify that the IP address for each VPN peer is accurate: This option would help to identify the root cause of a phase-1 negotiation failure, not a phase-2 negotiation failure. The IP address for each VPN peer is used to establish the IKE gateway, which is part of the phase-1 negotiation. If the IP address is inaccurate, the phase-1 negotiation will fail and the error message will be different.

Verify that the IP addresses can be pinged and that routing issues are not causing the connection failure: This option would also help to identify the root cause of a phase-1 negotiation failure, not a phase-2 negotiation failure. The ability to ping and route between the IP addresses of the VPN peers is a prerequisite for establishing the IKE gateway, which is part of the phase-1 negotiation. If there are routing issues or connectivity problems, the phase-1 negotiation will fail and the error message will be different.

In the IPSec Crypto profile configuration, verify that PFS is either enabled on both VPN peers or disabled on both VPN peers: This option would help to identify the root cause of a different phase-2 negotiation failure, not the one related to Proxy ID mismatch. PFS stands for Perfect Forward Secrecy, which is an option to generate a new encryption key for each IPSec session. If PFS is enabled on one

VPN peer but disabled on another, the phase-2 negotiation will fail and the error message will be "IKEv2 IPSec SA negotiation failed. Invalid syntax."3.

Reference: 1:

https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClbXCAS 2:

https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-admin/vpn/site-to-site-vpn/set-up-a-site-tosite-vpn-between-two-firewalls/policy-based-vpn 3:

https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClZSCA0