What are two characteristics of L2 circuits? (Choose two.)
A.
Routing instance configuration is required for L2 circuits to function correctly.
B.
Routing instance configuration is not required for L2 circuits to function correctly.
C.
BGP is required for L2 circuits to function correctly.
D.
BGP is not required for L2 circuits to function correctly.
Explanation:
B: You configure Layer 2 VPNs in a routing instance. As a result, Layer 2 VPNs have unique site and VPN
identifiers. However, Layer 2 circuits do not require a routing instance configuration and instead use an
alternate method of identifying circuits.
D: Layer 2 VPNs, like Layer 3 VPNs, require Border Gateway Protocol (BGP) for transport of traffic between PE
routers. In contrast, Layer 2 circuits do not require BGP. Instead, Layer 2 circuits rely on LDP and MPLS for
their operation.
http://www.juniper.net/techpubs/en_US/junos12.3/topics/concept/layer-two-circuits-overviewsolutions.html
B&D correct
Layer 2 circuits are very similar to Layer 2 VPNs. However, there are some significant differences:
You configure Layer 2 VPNs in a routing instance. As a result, Layer 2 VPNs have unique site and VPN identifiers. However, Layer 2 circuits do not require a routing instance configuration and instead use an alternate method of identifying circuits. Layer 2 circuit peer relationships are established with three components: a logical interface on the local PE router, the IP address of the remote PE router neighbor, and a virtual circuit identifier.
Layer 2 VPNs, like Layer 3 VPNs, require Border Gateway Protocol (BGP) for transport of traffic between PE routers. In contrast, Layer 2 circuits do not require BGP. Instead, Layer 2 circuits rely on LDP and MPLS for their operation. As a result, Layer 2 circuits require less configuration than Layer 2 VPNs.
https://www.juniper.net/documentation/en_US/junos12.3/topics/concept/layer-two-circuits-overview-solutions.html
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B & D, Final answer.
Two steps to configure layer 2 circuit.
1. Enable a Layer 2 circuit on the appropriate interface.
‘set protocols l2circuit neighbor interface-name interface interface-name’
2. Enter the circuit ID number.
‘set protocols l2circuit neighbor interface-name interface interface-name virtual-circuit-id id-number’
of course, you should know to “commit check” and “commit” an all configurations.
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