Juniper JN0-664 Practice Test - Questions Answers, Page 3

PIM sparse mode (PIM-SM) is a multicast routing protocol that uses a pull model to deliver multicast traffic. In PIM-SM, routers with receivers send join messages to their upstream neighbors toward a rendezvous point (RP) or a source-specific tree (SPT). The RP or SPT acts as the root of a shared distribution tree for a multicast group. Traffic is only forwarded to routers that request to join the distribution tree by sending join messages. PIM-SM does not flood traffic to all routers or prune routers without receivers, as PIM dense mode does.

the default behavior for iBGP is to propagate EBGP-learned prefixes without changing the next-hop. This can cause issues if the next-hop is not reachable via the IGP. One solution is to use the next-hop self command on R4, which will change the next-hop attribute to its own loopback address. This way, R5 can reach the next-hop via the IGP and install the route in its routing table.

Another solution is to add the external interface prefix (120.0.4.16/30) to the IGP routing tables of R4 and R5. This will also make the next-hop reachable via the IGP and allow R5 to use the route.According to2, this is a possible workaround for a pure IP network, but it may not work well for an MPLS network.

The reason why the route is being hidden is that R5 cannot reach the BGP next hop 10.0.0.1, which is the address of R1. R5 does not have a route to 10.0.0.0/24 in its routing table, and neither does R4. Therefore, R5 cannot resolve the BGP next hop and marks the route as hidden.

There are two solutions that will solve this problem:

Option A: On R4, create a policy to change the BGP next hop to itself and apply it to IBGP as an export policy. This way, R5 will receive the route with a next hop of 172.16.1.2, which is reachable via the IGP.This solution is also known as next-hop-self1.

Option B: Add the external interface prefix to the IGP routing tables. This way, R4 and R5 will learn a route to 10.0.0.0/24 via the IGP and be able to resolve the BGP next hop.This solution is also known as recursive lookup2.

Option C is not correct because adding the internal interface prefix to the BGP routing tables will not help R5 reach the BGP next hop 10.0.0.1.

Option D is not correct because changing the BGP next hop to 172.16.1.1 on R4 will not help R5 either, since R5 does not have a route to 172.16.1.1 in its routing table.

AToM (Any Transport over MPLS) is a framework that supports various Layer 2 transport types over an MPLS network core. One of the transport types supported by AToM is LDP Layer 2 circuit, which is a point-to-point Layer 2 connection that uses LDP for signaling and MPLS for forwarding. LDP Layer 2 circuit can support Layer 2 connectivity without using BGP and can be scalable and efficient by using a single MPLS LSP for multiple VPN connections. The customer can maintain all routing for their private network by using their own CE switches.

IS-IS routers can form Level 1 or Level 2 adjacencies depending on their configuration and network topology. Level 1 routers are intra-area routers that share the same area address with their neighbors. Level 2 routers are inter-area routers that can connect different areas. Level 1-2 routers are both intra-area and inter-area routers that can form adjacencies with any other router.

In the exhibit, R1 and R2 are in different areas (49.0001 and 49.0002), so they cannot form a Level 1 adjacency. However, they can form a Level 2 adjacency if they are both configured as Level 1-2 routers. R1 is already configured as a Level 1-2 router, but R2 is configured as a Level 1 router only, because of the level 1 disable command under the lo0.0 interface. This command disables Level 2 routing on the loopback interface, which is used as the router ID for IS-IS.

Therefore, to establish a Level 1 adjacency between R1 and R2, the level 1 disable command under the R2 protocols isis interface lo0.0 hierarchy must be removed. This will enable Level 2 routing on R2 and allow it to form a Level 2 adjacency with R1.

amplification attacks are a type of distributed denial-of-service (DDoS) attack that exploit the characteristics of certain protocols to amplify the traffic sent to a victim. For example, an attacker can send a small DNS query with a spoofed source IP address to a DNS server, which will reply with a much larger response to the victim. This way, the attacker can generate a large amount of traffic with minimal resources.

One of the methods to protect against amplification attacks is destination-based Remote Triggered Black Hole (RTBH) filtering. This technique allows a network operator to drop traffic destined to a specific IP address or prefix at the edge of the network, thus preventing it from reaching the victim and consuming bandwidth and resources. RTBH filtering can be implemented using BGP to propagate a special route with a next hop of 192.0.2.1 (a reserved address) to the edge routers. Any traffic matching this route will be discarded by the edge routers.

According to1and2, 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 the output shown in the exhibit, we can see some information about the L2VPN RIB and the pseudowire state. Based on this information, we can infer the following statements:

The PE is attached to a single local site. This is correct because the output shows only one local site ID (1) under the L2VPN RIB section. A local site ID is a unique identifier for a site within a VPLS domain. If there were multiple local sites attached to the PE, we would see multiple local site IDs with different prefixes.

The connection has not flapped since it was initiated. This is correct because the output shows that the uptime of the pseudowire is equal to its total uptime (1w6d). This means that the pseudowire has been up for one week and six days without any interruption or flap.

There has been a VLAN ID mismatch. This is not correct because the output shows that the remote and local VLAN IDs are both 0 under the pseudowire state section. A VLAN ID mismatch occurs when the remote and local VLAN IDs are different, which can cause traffic loss or misdelivery. If there was a VLAN ID mismatch, we would see different values for the remote and local VLAN IDs.

The PE router has the capability to pop flow labels. This is correct because the output shows that the flow label pop bit is set under the pseudowire state section. The flow label pop bit indicates that the PE router can pop (remove) the MPLS flow label from the packet before forwarding it to the CE device. The flow label is an optional MPLS label that can be used for load balancing or traffic engineering purposes.

BGP route target filtering can be configured on PE devices or on route reflectors (RRs). Configuring BGP route target filtering on RRs is more efficient and scalable, as it reduces the number of BGP sessions and updates between PE devices. To configure BGP route target filtering on RRs, the following steps are required:

Configure the family route-target statement under the BGP group or neighbor configuration on the RRs. This enables the exchange of the route-target address family between the RRs and their clients (PE devices). Configure the resolution rib bgp.l3vpn.0 resolution-ribs inet.0 statement under the routing-options configuration on the RRs. This enables the RRs to resolve next hops for VPN routes using the inet.0 routing table.

EVPN is a solution that provides Ethernet multipoint services over MPLS networks. EVPN uses BGP to distribute endpoint provisioning information and set up pseudowires between PE devices. EVPN uses different route types to convey different information in the control plane. The following are the main EVPN route types:

Type 1 - Ethernet Auto-Discovery Route: This route type is used for network-wide messaging and discovery of other PE devices that are part of the same EVPN instance. It also carries information about the redundancy mode and load balancing algorithm of the PE devices.

Type 2 - MAC/IP Advertisement Route: This route type is used for MAC and IP address learning and advertisement between PE devices. It also carries information about the Ethernet segment identifier (ESI) and the label for forwarding traffic to the MAC or IP address.

Type 3 - Inclusive Multicast Ethernet Tag Route: This route type is used for broadcast, unknown unicast, and multicast (BUM) traffic forwarding. It also carries information about the multicast group and the label for forwarding BUM traffic.

Type 4 - Ethernet Segment Route: This route type is used for multihoming scenarios, where a CE device is connected to more than one PE device. It also carries information about the ESI and the designated forwarder (DF) election process.

IS-IS is a link-state routing protocol that uses the Dijkstra algorithm to compute the shortest paths between nodes in a network. The Dijkstra algorithm maintains three data structures: a tree database, a candidate database, and a link-state database (LSDB). The tree database contains the nodes that have been visited and their shortest distances from the source node. The candidate database contains the nodes that have not been visited yet and their tentative distances from the source node. The LSDB contains the topology information of the network, such as the links and their costs.

The Dijkstra algorithm works as follows:

The local router moves its own local tuples into the tree database. A tuple consists of a node ID, a distance, and a parent node ID. The local router's tuple has a distance of zero and no parent node.

The local router moves its neighbors' tuples into the candidate database. The neighbors' tuples have distances equal to the costs of the links to them and parent node IDs equal to the local router's node ID.

The local router selects the tuple with the lowest distance from the candidate database and moves it to the tree database. This tuple becomes the current node.

The local router updates the distances of the current node's neighbors in the candidate database by adding the current node's distance to the link costs. If a shorter distance is found, the parent node ID is also updated.

The algorithm repeats steps 3 and 4 until either the destination node is reached or the candidate database is empty.