Exam JN0-661 topic 1 question 1 discussion

Actual exam question from Juniper's JN0-661

Question #: 1
Topic #: 1

Click the Exhibit button.
[edit]
user@PE-1# run show l2 circuit connections
Layer-2 Circuit Connections:
Legend for connection status (St)
EI - - encapsulation invalid NP - - interface h/w not present
MM - - mtu mismatch Dn - - down
EM - - encapsulation mismatch VC-Dn - -

Virtual circuit Down -
CM - - control-word mismatch Up - -
operational
VM - - vlan id mismatch CF - - Call
admission control failure
OL - - no outgoing label IB - - TDM
incompatible bitrare
NC - - intf encaps not CCC/TCC TM - - TDM
misconfiguration
BK - - Backup Connection ST - - Standby

Connection -
CB - - rcvd cell-bundle size bad SP - - Static

Pseudowire -
LD - - local site signaled down RS - - remote
site standby
RD - - remote site signaled down XX - - unknown

Legend for interface status -

Up - - operational -

Dn - - down -

Neighbor: 4.4.4.4 -
Interface Type St Time
last up #Up trans
ge-0/0/1.512 (vc 1) rmt OL
[edit]
user@PE-1# show protocols ldp
interface ge-0/0/2.0;
[edit]
user@PE-1# show protocols l2circuit
neighbor 4.4.4.4 {
interface ge-0/0/1.512 {
virtual-circuit-id 1
}
}
[edit]
user@PE-1# show interfaces ge-0/0/1
vlan-tagging;
encapsulation vlan-ccc;
unit 512 {
encapsulation vlan-ccc;
vlan-id 512;
}
[edit]
uxer@P-1 # show protocols ldp
interface all;
[edit]
user@P-2# show protocols ldp
interface all;
[edit]
user@PE-2# run show l2circuit connections
Layer-2 Circuit Connections:
Legend For connection status (St)
EI - - encapsulation invalid NP - - interface h/w not present
MM - - mtu mismatch Dn - - down
EM - - encapsulation mismatch VC-Dn - -

Virtual circuit Down -
CM - - control-word mismatch Up - -
operational
VM - - vlan id mismatch CF - - Call
admission control failure
OL - - no outgoing label IB - - TDM
incompatible bitrate
NC - - intf encaps not CCC/TCC TM - - TDM
misconfiguration
BK - - Backup Connection ST - - Standby

Connection -
CB - - rcvd cell-bundle size bad SP - - Static

Psewdowire -
LD - - Local site signaled down RS - - remote
site standby
RD - - remote site signaled down XX - - unknown

Legend for interface status -

UP - - operational -

DN - - down -

Neighbor: 1.1.1.1 -
Interface Type St Time
last up #Up trans
ge-0/0/1.512 (vc 1) rmt OL
[edit]
user@PE-2# show protocols ldp
interface ge-0/0/2.0;
[edit]
user@PE-2# show protocols l2circuit
neighbor 1.1.1.1 {
interface ge-0/0/1.512 {
virtual-circuit-id 1;
}
}
[edit]
user@PE-2# show interfaces ge-0/0/1
vlan-tagging;
encapsulation vlan-ccc;
unit 512 {
encapsulation vlan-ccc;
vlan-id 512;
}
Referring to the exhibit, you have configured an L2 circuit that connects Site-1 and Site-2, but the L2 circuit is not functioning. The topology in this scenario is shown below.
Site-1 > PE-1 > P-1 > P-2 > PE-2 Site-2
Which action will allow communication between Site-1 and Site-2?

A. Change the virtual circuit identifier to 2 for PE-2.
B. Add the family inet statement under the ge-0/0/1.512 interface for PE-1 and PE-2.
C. Add the lo0 interface under the {edit protocols ldp} hierarchy for all routers.
D. Add the lo0 interface under the {edit protocols 12circuit} hierarchy for PE-1 and PE-2

Show Suggested Answer

Suggested Answer: C 🗳️
LDP is required as the signaling protocol for Layer 2 circuits. You must include the loopback address in LDP. We enable ldp on the loopback interfaces.
Incorrect Answers:
A: The virtual circuit identifer is correctly set to 1 both at PE-1 and PE-2.
References:
https://www.juniper.net/techpubs/en_US/junos12.3/topics/example/layer-two-circuits-ethernet-configuring-detailed-solutions.html

by lugiricy at April 4, 2025, 8:22 p.m.

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