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Exam 350-501 topic 1 question 220 discussion

Actual exam question from Cisco's 350-501
Question #: 220
Topic #: 1
[All 350-501 Questions]


Refer to the exhibit. An Ethernet access provider is configuring routers PE-1 and PE-2 to provide E-Access EVPL service between UNI and ENNI. ENNI service multiplexing is based on 802.1ad tag 150, and service-multiplexed UNI is based on 802.1q tag 10. Which EFP configurations must the provider implement on PE-1 and PE-2 to establish end-to-end connectivity between CE-1 and CE-2?

  • A. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 rewrite ingress tag pop 1 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10
  • B. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1q 150 rewrite ingress tag pop 1 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10
  • C. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 dot1q 10 rewrite ingress tag pop 2 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10
  • D. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 rewrite ingress tag pop 1 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10 rewrite ingress tag pop 1 symmetric
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Suggested Answer: A 🗳️
by ccie_race at Oct. 22, 2022, 2:15 p.m.

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cipikacipiki
Highly Voted 2 years, 1 month ago
none of the options are the answer, I tested in the lab, it should be this way On PE-1: interface GigabitEthernet2 service instance 150 ethernet (>>> so we get Gi2:150 (Eth VLAN), follow the exhibit) encapsulation dot1ad 150 dot1q 10 rewrite ingress tag pop 2 symmetric On PE-2: interface GigabitEthernet2 service instance 10 ethernet (>>> so we get Gi2:10 (Eth VLAN), follow the exhibit) encapsulation dot1q 10 rewrite ingress tag pop 1 symmetric
upvoted 8 times
karen1337
1 year, 1 month ago
I got this working in the lab. If you want to do it, CE-1 has to be IOS-XR. It's the only platform that allows that type of config. For a simple lab, you can configure this like a L2VPN. Add xconnect statements to the service instances on PE-1 and PE-2. Answer A is the only way that worked in my lab. It works like this: - We don't need to do anything to the dot1q tag since it's the same on both sides. - We need to pop and add the dot1ad tag on the PE-1 side.
upvoted 3 times
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mr_warrior
1 year, 8 months ago
you are right. or pop 1 sym on PE-1 and no tag manipulation on PE-2.
upvoted 1 times
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Mo_El
Highly Voted 1 year, 10 months ago
Should be A. dot1q 10 is preserved from both sides and only extra S-tag on PE1 side is stripped/pushed. https://www.examtopics.com/discussions/cisco/view/86192-exam-350-501-topic-1-question-220-discussion/# Answer C is wrong, CE2 will be receiving untagged traffic where it expects tagged with vlan 10.
upvoted 6 times
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sushil_bhattacharjee
Most Recent 9 months, 1 week ago
Selected Answer: A
Answer A
upvoted 1 times
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ariasse
1 year, 6 months ago
Well, I agree that none of the answers are correct, but the command on PE2 should be rewrite ingress tag pop 1 symmetric to keep tag 10: https://www.cisco.com/c/en/us/td/docs/routers/asr920/configuration/guide/ce/17-1-1/b-ce-xe-17-1-asr920/b-ce-xe-17-1-asr920_chapter_010.html "Rewrite Operations You can use the rewrite command to modify packet VLAN tags. You can use this command to emulate traditional 802.1Q tagging, where packets enter a router on the native VLAN and VLAN tagging properties are added on egress. You can also use the rewrite command to facilitate VLAN translation and QinQ. The supported rewrite commands: rewrite ingress tag pop 1 symmetric rewrite ingress tag pop 2 symmetric rewrite ingress tag push dot1q vlan-id symmetric Enter the rewrite ingress tag pop {1 | 2} symmetric service-instance configuration mode command to specify the encapsulation adjustment to be performed on the frame ingress to the EFP. Entering pop 1 pops (removes) the outermost tag; entering pop 2 removes two outermost tags."
upvoted 2 times
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mr_warrior
1 year, 9 months ago
https://community.cisco.com/t5/networking-knowledge-base/understanding-ethernet-virtual-circuits-evc/ta-p/3108219
upvoted 1 times
thejag
1 year, 9 months ago
Thanks for the reference. Do you agree with C also?
upvoted 1 times
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nottoday2077
1 year, 10 months ago
Selected Answer: A
A - Pop outer tag, leaves inner 10. No tag manipulation needed on PE-2/CE-2 side. B - dot1q instead of dot1ad. C - Your popping both tags leaving an untagged packet with no symmetric on PE-2 side. D - PE-2 side your popping your inner tag that would be for PE-1/CE-1.
upvoted 4 times
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cname404
2 years ago
B seems OK, PE2 doesn''t do any tag manipulation, PE1 removes 150 on ingress and adds 150 on egrees (on the interface towards CE1) in order to match CE1 amd CE2 subinterfaces encapsulation.
upvoted 1 times
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mohdema
2 years, 1 month ago
Selected Answer: C
A. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 rewrite ingress tag pop 1 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10 B. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1q 150 rewrite ingress tag pop 1 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10 C. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 dot1q 10 rewrite ingress tag pop 2 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10 D. On PE-1: interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 rewrite ingress tag pop 1 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10 rewrite ingress tag pop 1 symmetric
upvoted 1 times
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ccie_race
2 years, 1 month ago
C interface GigabitEthernet2 service instance 100 ethernet encapsulation dot1ad 150 dot1q 10 rewrite ingress tag pop 2 symmetric On PE-2: interface GigabitEthernet2 service instance 2 ethernet encapsulation dot1q 10
upvoted 1 times
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