The provided configuration is for a routing instance named VPN-A on a Juniper PE (Provider Edge) router. Let’s break it down:
Instance Type: VRF
The instance-type vrf; statement indicates that this is a Layer 3 VPN (L3VPN) using MPLS VPNs (RFC 4364 – BGP/MPLS IP VPNs).
This confirms that Option D (A Layer 3 VPN is configured) is correct ✅.
VRF Target and Interface Association
The vrf-target target:64512:1234; defines the route target (RT) for importing and exporting VPN routes.
The interface ge-0/0/1.0; binds this interface to the VRF.
BGP Configuration for CE (Customer Edge) Peering
The group CE section configures external BGP (EBGP) (type external;).
The neighbor 10.0.0.1 is in AS 64512 (peer-as 64512;).
The as-override; statement is used.
Evaluating the Answer Choices
✅ Option B: "This VPN connects customer sites that use the same AS number."
The as-override; command allows multiple customer sites that use the same AS number (64512) to communicate over the service provider’s MPLS network.
Normally, BGP prevents routes with the same AS in the AS_PATH from being accepted. The as-override feature replaces the customer's AS number with the provider’s AS, ensuring proper route advertisement.
✅ This statement is correct.
❌ Option A: "This VPN connects customer sites that use different AS numbers."
If the customer sites had different AS numbers, there would be no need for as-override.
The as-override feature is specifically used when all customer sites share the same AS number, ensuring that BGP routes are accepted.
❌ This statement is incorrect.
❌ Option C: "A Layer 2 VPN is configured."
A Layer 2 VPN (L2VPN) configuration would typically use instance-type l2vpn; or EVPN/VPLS-related parameters (e.g., protocols l2vpn or protocols vpls).
Since this configuration uses instance-type vrf; and BGP with a VRF target, it is clearly a Layer 3 VPN (L3VPN).
❌ This statement is incorrect.
✅ Option D: "A Layer 3 VPN is configured."
The instance-type vrf; confirms this is an MPLS Layer 3 VPN (L3VPN).
VRFs, BGP, and route targets (vrf-target) are specific to Layer 3 VPNs.
✅ This statement is correct.
Final Answer:
✅ B. This VPN connects customer sites that use the same AS number.
✅ D. A Layer 3 VPN is configured.
Verification from Juniper Documentation:
Juniper BGP/MPLS Layer 3 VPNs Guide confirms that instance-type vrf is used for L3VPNs.
Juniper BGP Configuration Guide states that as-override is applied when customer sites use the same AS number.
RFC 4364 (BGP/MPLS IP VPNs) explains how route targets and VRFs are used in L3VPN deployments.
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