Exam 350-501 topic 1 question 220 discussion

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

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.

Answer A

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."

https://community.cisco.com/t5/networking-knowledge-base/understanding-ethernet-virtual-circuits-evc/ta-p/3108219

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.

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.

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

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