Juniper JN0-664 Exam Dumps

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

https://www.juniper.net/documentation/us/en/software/junos/sampling-forwarding-monitoring/bgp/topics/concept/bgp-multipath-unequal-understanding.html

Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol that supports Level 1 (L1), Level 2 (L2), or both (L1/L2) operations. The way IS-IS sends Hello (IIH) packets depends on whether the interface is point-to-point (P2P) or broadcast (LAN).

Evaluating the Answer Choices

Option A: 'If a point-to-point interface is in both L1 and L2, separate hello messages are sent for each level.'

Incorrect!

On point-to-point (P2P) interfaces, only one combined Hello message is sent for both L1 and L2.

IS-IS P2P Hellos include both Level 1 and Level 2 TLVs in the same message.

This statement is incorrect.

Option B: 'If a point-to-point interface is in both L1 and L2, one combined hello message is sent for both levels.'

Correct!

On point-to-point (P2P) links, IS-IS sends a single Hello message that includes TLVs for both L1 and L2.

This reduces overhead and simplifies adjacency formation.

This statement is correct.

Option C: 'If a broadcast interface is in both L1 and L2, separate hello messages are sent for each level.'

Correct!

On broadcast (LAN) interfaces, IS-IS sends separate Hello messages for L1 and L2.

This is because L1 and L2 use separate Designated IS (DIS) elections and different multicast addresses:

L1 Hellos: Sent to AllL1IS (01:80:C2:00:00:14)

L2 Hellos: Sent to AllL2IS (01:80:C2:00:00:15)

This statement is correct.

Option D: 'If a broadcast interface is in both L1 and L2, one combined hello message is sent for both levels.'

Incorrect!

As stated above, IS-IS sends separate Hello messages for L1 and L2 on broadcast interfaces because they have independent DIS elections.

This statement is incorrect.

Final Answer:

B. If a point-to-point interface is in both L1 and L2, one combined hello message is sent for both levels. C. If a broadcast interface is in both L1 and L2, separate hello messages are sent for each level.

Verification from Juniper Documentation

Juniper IS-IS Configuration Guide confirms:

Point-to-Point (P2P) interfaces send one combined Hello for both levels.

Broadcast interfaces send separate L1 and L2 Hellos due to separate DIS elections.

RFC 1195 (IS-IS Extensions for IPv4) specifies that broadcast networks require distinct Hellos per level.

BGP Layer 2 VPNs use BGP to distribute endpoint provisioning information and set up pseudowires between PE devices. BGP uses the Layer 2 VPN (L2VPN) Routing Information Base (RIB) to store endpoint provisioning information, which is updated each time any Layer 2 virtual forwarding instance (VFI) is configured. The prefix and path information is stored in the L2VPN database, which allows BGP to make decisions about the best path.

In BGP Layer 2 VPNs, each site has a unique site ID that identifies it within a VFI. The site ID can be manually configured or automatically assigned by the PE device. By default, the site ID is automatically assigned based on the order that you add the interfaces to the site configuration. The first interface added to a site configuration has a site ID of 1, the second interface added has a site ID of 2, and so on.

Option D is correct because by default on PE-2, the remote site IDs are automatically assigned based on the order that you add the interfaces to the site configuration. Option A is not correct because by default on PE-2, the site's local ID is automatically assigned a value of 0 and does not need to be configured to match the total number of attached sites. Option B is not correct because you do not need to create a unique Layer 2 VPN routing instance for each site on the PE-2 device. You can create one routing instance for all sites within a VFI. Option C is not correct because you do not need to use separate physical interfaces to connect PE-2 to each site. You can use subinterfaces or service instances on a single physical interface.

The `vrf-target` statement in a Layer 3 VPN configuration is used to control the import and export of VPN routes by attaching a target community to the routes. This helps in defining which VPN routes should be imported into or exported from a particular VRF (Virtual Routing and Forwarding) instance.

1. **Understanding VRF Target**:

- The `vrf-target` statement specifies the extended community attributes (route targets) that are used to control the import and export of routes in a VRF.

- These attributes help in identifying which routes should be shared between different VRFs, particularly across different PE (Provider Edge) devices.

2. **Statements Analysis**:

- **A. This value is used to identify BGP routes learned from the local CE device.**

- Incorrect. The `vrf-target` attribute is not used to identify routes learned from the local CE device. It is used to manage routes between PE devices and within the provider's MPLS network.

- **B. This value is used to identify BGP routes learned from the remote PE device.**

- Correct. The `vrf-target` value helps in identifying which routes from remote PE devices should be imported into the local VRF. It essentially acts as a filter for importing BGP routes with matching target communities.

- **C. This value is used to add a target community to BGP routes advertised to the local CE device.**

- Incorrect. Routes advertised to the local CE device do not use the `vrf-target` attribute. Instead, these routes are typically managed within the local VRF routing table.

- **D. This value is used to add a target community to BGP routes advertised to the remote PE device.**

- Correct. When advertising routes from the local PE to remote PE devices, the `vrf-target` value is added to these routes. This target community ensures that the correct routes are shared across the VPN.

**Conclusion**:

The correct statements about the `vrf-target` configuration in a Layer 3 VPN scenario are:

**B. This value is used to identify BGP routes learned from the remote PE device.**

**D. This value is used to add a target community to BGP routes advertised to the remote PE device.**

**Reference**:

- Juniper Networks Documentation on VRF Target: [VRF Target Configuration](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/layer-3-vpns.html)

- MPLS and VPN Architectures by Ivan Pepelnjak and Jim Guichard