A PE provides VLAN VPLS service to a CE attached with two links. You want to prevent Layer 2 loops and
provide link redundancy.
Which two actions will accomplish this task? (Choose two.)
A.
Place both interfaces in a link aggregation group.
B.
Configure different VLANs on each interface.
C.
Configure all VLANs on both interfaces, on the PE, and on the CE.
D.
Configure Spanning Tree Protocol between the PE and the CE.
Explanation:
D: To prevent the formation of Layer 2 loops between the CE devices and the multihomed PE routers, Juniper
recommends that you employ the Spanning Tree Protocol (STP) on your CE devices. Layer 2 loops can form
due to incorrect configuration. Temporary Layer 2 loops can also form during convergence after a change in the
network topology.
http://www.juniper.net/documentation/en_US/junos16.1/topics/topic-map/vpls-bgpmultihoming.html
answer should be C & D
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Hi Adeshina Keshinro, most of the questions from your link have nottting to do with this exam, just a few questions are ok! please, here there is no place for spam!
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I would say A, D
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what about vlan configuration in LAG?
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I agree with cyx, answer A, D for me. Regarding VLAN configuration in LAG :
interfaces aex {
vlan-tagging;
encapsulation encapsulation-type;
unit logical-unit-number {
vlan-id number;
}
}
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Why would you suggest that A, D options are correct? I think having different VLANs in a way provides redundancy
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AD is correct answer,
Redundant Links Between CE and PE
The slide shows a potential loop situation that can occur when there are multiple links between a CE and the local PE. If CE-A2 is a router operating at Layer 3, then there should be no Layer 2 loop possible. However, if CE-A2 is a Layer 2 switch then a Layer 2 loop is possible. To prevent Layer 2 data from looping between the CE and PE with redundant links you must configure either a spanning tree protocol between PE and CE, active and backup links on the PE, Ethernet Ring Protection (ERP), or a link aggregation group (LAG).
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Yes, AD is the correct is part of the Potential Layer2 loops.
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C and D. there are two choices hence it has to be accomplished by using two configurations. if LAG is used then its done, we cannot select other choice.
if we choose STP (D), then the only option is C. Because STP blocks other port so if not all vlans are configured on the port then it cannot pass traffic for rest vlans
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https://www.juniper.net/documentation/en_US/junos/topics/topic-map/vpls-bgp-multihoming.html
The Per-VLAN Spanning Tree (PVST) protocol maintains a separate spanning-tree instance for each VLAN.
https://www.juniper.net/documentation/en_US/junos12.3/topics/task/configuration/vpls-stp-solutions.html
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I guess A & D , only C can not use alone , A or D can use alone.
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Option A and D, final answer.
In VPLS (point-to-multipoint) layer 2 technology, whenever you want to prevent loops and provide redundancy, you must do the following;
1. Configure Spanning-Tree Protocol
2. Configure a LAG.
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