Exam Professional Cloud Network Engineer All Questions

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Exam Professional Cloud Network Engineer topic 1 question 15 discussion

Actual exam question from Google's Professional Cloud Network Engineer

Question #: 15
Topic #: 1

[All Professional Cloud Network Engineer Questions]

Your on-premises data center has 2 routers connected to your Google Cloud environment through a VPN on each router. All applications are working correctly; however, all of the traffic is passing across a single VPN instead of being load-balanced across the 2 connections as desired.
During troubleshooting you find:
"¢ Each on-premises router is configured with a unique ASN.
"¢ Each on-premises router is configured with the same routes and priorities.
"¢ Both on-premises routers are configured with a VPN connected to a single Cloud Router.
"¢ BGP sessions are established between both on-premises routers and the Cloud Router.
"¢ Only 1 of the on-premises router's routes are being added to the routing table.
What is the most likely cause of this problem?

A. The on-premises routers are configured with the same routes.
B. A firewall is blocking the traffic across the second VPN connection.
C. You do not have a load balancer to load-balance the network traffic.
D. The ASNs being used on the on-premises routers are different.

Show Suggested Answer

Suggested Answer: D 🗳️

by Jos at June 22, 2020, 9:53 a.m.

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glk

Highly Voted 4 years, 1 month ago

Answer is D: Cloud Router doesn't use ECMP across routes with different origin ASNs For cases where you have multiple on-premises routers connected to a single Cloud Router, the Cloud Router learns and propagates routes from the router with the lowest ASN. Cloud Router ignores advertised routes from routers with higher ASNs, which might result in unexpected behavior. For example, you might have two on-premises routers advertise routes that are using two different Cloud VPN tunnels. You expect traffic to be load balanced between the tunnels, but Google Cloud uses only one of the tunnels because Cloud Router only propagated routes from the on-premises router with the lower ASN. reference: https://cloud.google.com/network-connectivity/docs/router/support/troubleshooting#ecmp

upvoted 16 times

AzureDP900

2 years, 2 months ago

Agree, D. The ASNs being used on the on-premises routers are different.

upvoted 1 times

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Windows98

Highly Voted 4 years, 2 months ago

D - GCP doesn't run ECMP across different ASNs

upvoted 9 times

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saraali

Most Recent 5 months, 3 weeks ago

Selected Answer: D

Reason:The correct answer is D. The ASNs being used on the on-premises routers are different. Cloud Router does not perform Equal-Cost Multi-Path (ECMP) routing across BGP sessions with different Autonomous System Numbers (ASNs). Cloud Router selects the BGP route from the router with the lowest ASN and ignores the routes from the router with the higher ASN. This leads to the observed issue where traffic is not load-balanced, leading to traffic being routed through just one VPN tunnel instead of being load-balanced across both. To resolve this, ensure that both on-premises routers use the same ASN for BGP sessions with Cloud Router

upvoted 1 times

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xhilmi

1 year, 1 month ago

Choose D: ASN (Autonomous System Number): An ASN is a unique identifier assigned to an autonomous system for the purpose of routing traffic on the Internet. In BGP (Border Gateway Protocol), each router in a network is assigned a unique ASN. To resolve this issue, ensure that both on-premises routers have the same ASN or use the same ASN for both routers if possible. This will help achieve the desired load balancing across the two VPN connections.

upvoted 3 times

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didek1986

1 year, 5 months ago

Selected Answer: D

All Cloud Routers that are associated with a single hub must use the same Google ASN. To select an ASN, follow the recommendations in the Cloud Router documentation.

upvoted 1 times

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rr4444

1 year, 6 months ago

Everyone is saying D, but that link saying only same ASN is needed no longer has that content Searched Google also Still the same now? Migth have changed, but I don't see anything Cloud Router or Cloud VPN release notes for

upvoted 2 times

rr4444

1 year, 6 months ago

Actually D The docs are in a totally different place https://cloud.google.com/network-connectivity/docs/network-connectivity-center/concepts/asn-requirements#asn_assignment

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pk349

2 years ago

D: Autonomous System Numbers: An Autonomous System (AS) is a set of Internet routable IP prefixes belonging to a network or a collection of networks that are all managed, controlled and supervised by a single entity or organization. Google Cloud uses only one of the tunnels because Cloud Router only propagated routes from the on-premises router with the lower ASN."

upvoted 2 times

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pfilourenco

2 years, 2 months ago

Selected Answer: D

The correct answer is D. Cloud Router doesn't use ECMP across routes with different origin ASNs

upvoted 1 times

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GCP72

2 years, 5 months ago

Selected Answer: D

The correct answer is D.

upvoted 1 times

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kumarp6

3 years, 1 month ago

Answer is : D

upvoted 2 times

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Vidyasagar

3 years, 10 months ago

D is right

upvoted 1 times

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groovygorilla

4 years, 1 month ago

Agree with glk, answer is D. This reference says it all: https://cloud.google.com/network-connectivity/docs/router/support/troubleshooting#ecmp Cloud Router doesn't use ECMP across routes with different origin ASNs Cloud Router doesn't use ECMP across routes with different origin ASNs Cloud Router doesn't use ECMP across routes with different origin ASNs

upvoted 2 times

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genesis3k

4 years, 3 months ago

Correct answer is D. Please refer below: "you might have two on-premises routers advertise routes that are using two different Cloud VPN tunnels. You expect traffic to be load balanced between the tunnels, but Google Cloud uses only one of the tunnels because Cloud Router only propagated routes from the on-premises router with the lower ASN." https://cloud.google.com/network-connectivity/docs/router/support/troubleshooting#ecmp

upvoted 3 times

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Aniyadu

4 years, 3 months ago

The answer seems to be D. As per standard practices we can only one ASN configured in on-premise. https://cloud.google.com/network-connectivity/docs/vpn/concepts/topologies

upvoted 1 times

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passtest100

4 years, 5 months ago

change to A. The BGP session is esblished. so B is wrong. BGP(EBGP and IBGP) by default has only one optimal route in routing table. So whether ASN is the same or different, the issue still exists. Only if the routes are different, routes of the two router will be in the routing table.

upvoted 1 times

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passtest100

4 years, 5 months ago

sorry，typo. it should be B is the possible answer.

upvoted 1 times

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passtest100

4 years, 5 months ago

should be C. no information in the question shows two ASNs is wrong. it should be reasonable that one data center can have multiple ASNs, since ASN has nothing to do with geo location. The two ASNs works well in the data center, as supposed in the question, the question is why the VPN with one of the router cannot be setup. so C is the only possible answer.

upvoted 1 times

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