Google Professional Cloud Network Engineer Question 745
Select 3Google Cloud PlatformYou have configured a Cloud Router to establish a BGP session with your on-premises router over a VPN tunnel. However, the BGP session does not establish, and you need to troubleshoot the issue. Which of the following steps should you perform to identify and resolve the problem?
- A
Verify that the BGP peer IP address on the Cloud Router matches the on-premises router's BGP IP address.
- B
Check the firewall rules to ensure that TCP port 179 is allowed between the on-premises router and the Cloud Router.
- C
Ensure that the Cloud Router's ASN matches the ASN of the on-premises router.
- D
Validate that the VPN tunnel is operational and the on-premises router can reach the Cloud Router's BGP peer IP.
- E
Verify that the maximum transmission unit (MTU) setting on the VPN tunnel is set to 1500 bytes.
Show answer and explanation
Correct answers: A, B, D
Explanation
To troubleshoot Cloud Router BGP peering issues, you must ensure proper configuration and connectivity between the Cloud Router and the on-premises router. Matching BGP peer IP addresses, allowing TCP port 179, and verifying VPN connectivity are critical steps. The ASN does not need to match, and MTU settings, while important for performance, do not typically prevent a BGP session from forming.
- A. Correct.
Correct: For a BGP session to establish, the BGP peer IP addresses configured on both ends must match. Mismatched IPs will prevent the session from forming.
- B. Correct.
Correct: BGP uses TCP port 179 for communication. If this port is blocked by a firewall, the BGP session will fail to establish.
- C. Incorrect.
Incorrect: The Cloud Router's ASN does not need to match the ASN of the on-premises router. In fact, they are often different and are configured accordingly.
- D. Correct.
Correct: If the VPN tunnel is down or there is no connectivity between the on-premises router and the Cloud Router's BGP peer IP, the BGP session cannot establish.
- E. Incorrect.
Incorrect: While MTU settings can affect packet fragmentation, they are not directly responsible for the failure of a BGP session to establish.