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Exam ANS-C00 topic 1 question 159 discussion

Exam question from Amazon's ANS-C00
Question #: 159
Topic #: 1
[All ANS-C00 Questions]

You need to find the MTU used by another instance, but tracepath is not working. You know the instance you are trying to tracepath has open security group and
NACL rules. Which protocol do you need to allow to access your instance to remedy this?

  • A. Protocol 6: TCP
  • B. Protocol 47: GRE
  • C. Protocol 17: UDP
  • D. Protocol 1: ICMP
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Suggested Answer: D 🗳️
You need to allow Protocol 1, ICMP, to access your instance. tracepath specifically needs the "destination unreachable" feature of ICMP.
by eeghai7thioyaiR4 at March 16, 2021, 12:27 p.m.
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alpha00007
Highly Voted 3 years, 8 months ago
Check the path MTU between two hosts You can check the path MTU between two hosts using the tracepath command, which is part of the iputils package that is available by default on many Linux distributions, including Amazon Linux. To check path MTU using tracepath Use the following command to check the path MTU between your EC2 instance and another host. You can use a DNS name or an IP address as the destination. If the destination is another EC2 instance, verify that the security group allows inbound UDP traffic. C
upvoted 9 times
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student2020
Highly Voted 3 years, 8 months ago
Answer is C Tested this with 2 instances. Tracepath was only successful after adding Allow UDP rule in SG. Adding ICMP rule had no effect.
upvoted 7 times
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hello_aws
Most Recent 2 years, 9 months ago
Selected Answer: C
agree with alpha00007,tracepath use udp
upvoted 1 times
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Huy
3 years, 7 months ago
Traceroute use ICMP and tracepath use UDP. Easy to miss this.
upvoted 5 times
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eeghai7thioyaiR4
3 years, 8 months ago
I guess D You can find an MTU for a path to a remote host using ping -Mdo -s <some size> <hostname>
upvoted 1 times
eeghai7thioyaiR4
3 years, 8 months ago
Tracepath works with UDP -> C
upvoted 4 times
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