Juniper JN0-664 - Service Provider Professional (JNCIP-SP)

The auto-export parameter is a routing option that allows a routing instance to share routes with other routing instances or the master routing table. The auto-export parameter automatically exports routes from one routing instance to another based on the route target communities attached to the routes. In this scenario, the 10.101.1.0/24 route will be shared if the auto-export parameter is configured under [edit routing-options] hierarchy level.

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/command/show-route-advertising-protocol.html

BGP route reflectors are BGP routers that are allowed to ignore the IBGP loop avoidance rule and advertise IBGP learned routes to other IBGP peers under specific conditions. BGP route reflectors can reduce the number of IBGP sessions and updates in a network by eliminating the need for a full mesh of IBGP peers. BGP route reflectors can have three types of peerings:

EBGP neighbor: A BGP router that belongs to a different autonomous system (AS) than the route reflector.

IBGP client neighbor: An IBGP router that receives reflected routes from the route reflector. A client does not need to peer with other clients or non-clients.

IBGP non-client neighbor: An IBGP router that does not receive reflected routes from the route reflector. A non-client needs to peer with other non-clients and the route reflector.

In the exhibit, we can see that RR1 and RR2 are route reflectors in the same AS with reachability redundancy. They have two types of peerings: EBGP neighbors (R1 and R4) and IBGP client neighbors (Client1, Client2, and Client3). RR1 and RR2 are also peered with each other as IBGP non-client neighbors.

EVPN is a technology that connects L2 network segments separated by an L3 network using a virtual Layer 2 network overlay over the Layer 3 network. EVPN uses BGP as its control protocol to exchange different types of routes for different purposes. Type 2 routes are used to advertise MAC address and IP address pairs learned using ARP snooping from the local CE devices. Type 3 routes are used to join a multicast tree to flood traffic such as broadcast, unknown unicast, and multicast (BUM) traffic.

A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone. To create a sham link, you need to configure the local and remote addresses of the PE routers under the [edit protocols ospf area area-id] hierarchy level1.

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospfv2-sham-links.html

The hello interval is the time interval between two consecutive hello packets sent by an OSPF router on an interface. The dead interval is the time interval after which a neighbor is declared down if no hello packets are received from it. These parameters must match between two OSPF routers for them to form an adjacency. In the exhibit, router R1 has a hello interval of 10 seconds and a dead interval of 40 seconds, while router R2 has a hello interval of 30 seconds and a dead interval of 120 seconds. This causes a mismatch and prevents them from becoming neighbors23.

The customer interface in an LDP-signaled pseudowire is the interface on the PE router that connects to the CE device. An LDP-signaled pseudowire is a type of Layer 2 circuit that uses LDP to establish a point-to-point connection between two PE routers over an MPLS network. The customer interface can have different encapsulation types depending on the type of traffic that is carried over the pseudowire. The encapsulation types are ethernet-ccc, vlan-ccc, extended-vlan-ccc, atm-ccc, frame-relay-ccc, ppp-ccc, cisco-hdlc-ccc, and tcc-ccc. Depending on the encapsulation type, the customer interface can accept or reject tagged or untagged frames in the data plane, and include or exclude VLAN tags in the control plane LDP advertisement. The following table summarizes the behavior of different encapsulation types:

Analyzing the Exhibit

The diagram represents BGP peering between:

AS 65512 (Enterprise Network)

AS 65511 (ISP-A)

R3 and R4 are peering with ISP-A using EBGP.

R1, R2, R3, and R4 are peering within AS 65512 using IBGP.

Understanding BGP Route Behavior

Option A: "By default, the next-hop value for these routes is not changed by ISP-A before being sent to R3." ❌

Incorrect!

EBGP behavior: When a BGP route is advertised via EBGP, the next-hop IP is changed to the router's own IP by default.

Since ISP-A is advertising routes via EBGP to R3, the next-hop is changed to ISP-A’s IP.

Thus, this statement is incorrect.

Option B: "The BGP local-preference value that is used by ISP-A is not advertised to R3." ✅

Correct!

BGP Local Preference (LOCAL_PREF) is an IBGP-only attribute.

Local Preference is NOT shared over EBGP because it is used within an AS to influence route selection.

ISP-A will not send LOCAL_PREF to R3, as R3 is in a different AS.

Thus, this statement is correct.

Option C: "All BGP attribute values must be removed before receiving the routes." ❌

Incorrect!

BGP does not remove all attributes when advertising routes. Some attributes are modified (e.g., next-hop, AS-PATH), but others (like MED, community) may be preserved.

Thus, this statement is incorrect.

Option D: "The next-hop value for these routes is changed by ISP-A before being sent to R3." ✅

Correct!

As per default EBGP behavior, the next-hop is changed when a route is advertised to an EBGP peer.

This means ISP-A changes the next-hop to its own IP before sending it to R3.

Thus, this statement is correct.

Final Answer:

✅ B. The BGP local-preference value that is used by ISP-A is not advertised to R3.

✅ D. The next-hop value for these routes is changed by ISP-A before being sent to R3.

Verification from Juniper Documentation:

Juniper BGP Configuration Guide confirms that LOCAL_PREF is not advertised over EBGP.

RFC 4271 (BGP-4) specifies that next-hop is changed by default when advertising routes via EBGP.

The exhibit shows the configuration of a VRF (Virtual Routing and Forwarding) instance on a Juniper PE router. Let's break down the key components:

VRF Configuration (VPN-A)

The instance type is VRF, meaning this is an L3VPN (Layer 3 VPN).

The routing instance contains a static route (10.1.0.0/16 next-hop 10.1.0.1).

The interface ge-0/0/2.0 is assigned to the VRF.

Route Distinguisher (RD): 172.17.20.1:1

VRF-Export Policy: vpn-a-export

VRF-Target: target:65512:1 (This defines which routes will be imported into the VRF).

VRF Export Policy (vpn-a-export)

The vpn-a-export policy adds two BGP communities (route targets) to exported VPN routes:

community add vpn-a-target;

community add vpn-m-target;

accept;

The vpn-a-target community corresponds to target:65512:1.

The vpn-m-target community corresponds to target:65512:2.

Policy-Options (Community Definitions)

community vpn-a-target members target:65512:1;

community vpn-m-target members target:65512:2;

This confirms that routes exported from this VRF will have BOTH target:65512:1 and target:65512:2.

Evaluating the Answer Choices

✅ Option A: "VPN routes are exported with the target:65512:1 and target:65512:2 route targets."

The vpn-a-export policy explicitly adds both vpn-a-target (65512:1) and vpn-m-target (65512:2) to exported routes.

This is correct. ✅

❌ Option B: "You cannot use the vrf-target and vrf-export statements in the same VRF."

This is incorrect.

Juniper allows the use of both vrf-target and vrf-export in the same VRF:

vrf-target is used for importing routes.

vrf-export defines export policies (which can add additional route targets).

This is incorrect. ❌

❌ Option C: "VPN routes with the target:65512:1 and target:65512:2 route targets are imported."

The vrf-target target:65512:1; statement only controls importing routes.

The import policy does not include target:65512:2, so routes tagged with target:65512:2 alone would not be imported into this VRF.

This is incorrect. ❌

❌ Option D: "VPN routes are exported with only the target:65512:1 route target."

The export policy (vpn-a-export) clearly adds both 65512:1 and 65512:2.

This is incorrect. ❌

Final Answer:

✅ A. VPN routes are exported with the target:65512:1 and target:65512:2 route targets.

Verification from Juniper Documentation

Juniper MPLS L3VPN Configuration Guide confirms that vrf-target is used for importing, while vrf-export can be used for exporting multiple route targets.

Juniper Routing Policy Documentation states that export policies can add multiple BGP communities (route targets).

RFC 4364 (BGP/MPLS IP VPNs) defines the use of route targets for VPN route control.

For a Layer 3 VPN to function correctly, an MPLS Label Switched Path (LSP) must be established between the Provider Edge (PE) routers. The MPLS LSP is necessary for the transport of VPN traffic across the service provider's backbone network. If the MPLS LSP is not established, the PE routers cannot forward the VPN traffic properly, causing the routes to be hidden in the BGP routing table.

Here’s a breakdown of why the other options are less likely:

A. The routes use overlapping IP addresses.

Overlapping IP addresses might cause issues with route advertisement and selection, but they would not typically cause routes to be hidden in the bgp.l3vpn.0 table.

C. There is a routing loop in the service provider backbone.

While routing loops are problematic, they would not specifically cause the routes to be hidden in the bgp.l3vpn.0 table. Routing loops would more likely result in dropped packets or increased latency.

D. Route targets are not configured.

Incorrect or missing route target configuration would prevent routes from being imported into the correct VRF, but it would not usually result in the routes being hidden. Instead, they would simply not appear in the relevant VRF.

Thus, the absence of an established MPLS LSP is the most plausible cause for the routes being hidden.