Exam Code: 400-101 (Practice Exam Latest Test Questions VCE PDF)
Exam Name: CCIE Routing and Switching (v5.0)
Certification Provider: Cisco
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2021 Jun 400-101 Study Guide Questions:

Q441. Refer to the exhibit. 


Assuming that the peer is configured correctly and the interface is up, how many neighbors will be seen in the EIGRPv6 neighbor table on this IPv6-only router? 

A. one neighbor, which will use a local router-id of 6010. AB8. . /64 

B. one neighbor, which will use a local router-id of 6020. AB8. . /64 

C. none, because EIGRPv6 only supports authenticated peers 

D. none, because of the mismatch of timers 

E. none, because there is no EIGRP router ID configured 

Answer: E 

Explanation: 

Configuring EIGRP for IPv6 has some restrictions; they are listed below: 

. The interfaces can be directly configured with EIGRP for IPv6, without the use of a global IPv6 address. There is no network statement in EIGRP for IPv6. 

. The router ID needs to be configured for an EIGRPv6 protocol instance before it can run. 

. EIGRP for IPv6 has a shutdown feature. Ensure that the routing process is in "no shut" mode to start running the protocol. 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/113267-eigrp-ipv6-00.html 


Q442. Which statement about the BGP originator ID is true? 

A. The route reflector always sets the originator ID to its own router ID. 

B. The route reflector sets the originator ID to the router ID of the route reflector client that injects the route into the AS. 

C. The route reflector client that injects the route into the AS sets the originator ID to its own router ID. 

D. The originator ID is set to match the cluster ID. 

Answer: B 

Explanation: 

An RR reflecting the route received from a RR-Client adds: 

. Originator ID- a 4-byte BGP attribute that is created by the RR. This attribute carries the Router ID of the originator of the route in the local AS. If the update comes back to the originator, it ignores the update. 

. Cluster List- A Cluster List is a list of Cluster IDs that an update has traversed. When a route reflector sends a route received from a client to a non-client, it appends the local Cluster ID. If a route reflector receives a route whose Cluster List contains the local Cluster ID, it ignores the update. 

Reference: https://sites.google.com/site/amitsciscozone/home/bgp/bgp-route-reflectors 


Q443. Which statement about the EIGRP RTO is true? 

A. It is six times the SRTT. 

B. It is the time that it normally takes for an update to be received by a peer. 

C. It is the time that it normally takes to receive a reply to a query. 

D. It is the average time that it takes for a reliable packet to be acknowledged. 

Answer: A 

Explanation: 

The RTO is typically six times the SRTT, the value may vary from a minimum of 200 microseconds (ms) to a maximum of 5 seconds (s). 

Reference: EIGRP for IP: Basic Operation and Configuration, Alvaro Retana, Russ White, Don Slice - 2000 


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Q444. MPLS LDP IGP synchronization is configured on a link. The OSPF adjacency on that link is UP but MPLS LDP synchronization is not achieved. Which statement about this scenario is true? 

A. The router excludes the link from its OSPF LSA type 1. 

B. The router flushes its own router LSA. 

C. The router advertises the link in its router LSA with max-metric. 

D. The router advertises an LSA type 2 for this link, with the metric set to max-metric. 

E. The router advertises the link and OSPF adjacency as it would when the synchronization is achieved. 

Answer: C 

Explanation: 

To enable LDP-IGP Synchronization on each interface that belongs to an OSPF or IS-IS process, enter the mpls ldp sync command. If you do not want some of the interfaces to have LDP-IGP Synchronization enabled, issue the no mpls ldp igp sync command on those interfaces. If the LDP peer is reachable, the IGP waits indefinitely (by default) for synchronization to be achieved. To limit the length of time the IGP session must wait, enter the mpls ldp igp sync holddown command. If the LDP peer is not reachable, the IGP establishes the adjacency to enable the LDP session to be established. When an IGP adjacency is established on a link but LDP-IGP Synchronization is not yet achieved or is lost, the IGP advertises the max-metric on that link. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fsldpsyn.html 


Q445. Which two descriptions of the keying mechanisms that are used to distribute the session keys used in routing authentication are true? (Choose two.) 

A. Peer keying creates a unique one-to-one relationship with another peer. 

B. Group keying creates a single keying message to multiple peers. 

C. Peer keying creates a single keying message to multiple peers. 

D. Group keying creates a unique one-to-one relationship with another peer. 

E. Group keying creates a full mesh of keying sessions to all devices. 

F. Peer keying creates a full mesh of keying sessions to all devices. 

Answer: A,B 


Q446. What is the range of addresses that is used for IPv4-mapped IPv6 addresses? 

A. 2001. db9. . /32 

B. 2001. db8. . /32 

C. 2002. . /16 

D. . . ffff. /16 

E. . . ffff. 0. 0/96 

Answer: E 

Explanation: 

IPv4-Mapped Addresses FFFF:0:0/96 are the IPv4-mapped addresses [RFC4291]. Addresses within this block should not appear on the public Internet. 

Reference: https://tools.ietf.org/html/rfc5156 


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Q447. Refer to the exhibit. 


Which AS paths are matched by this access list? 

A. the origin AS 64496 only 

B. the origin AS 64496 and any ASs after AS 64496 

C. the directly attached AS 64496 and any ASs directly attached to AS 64496 

D. the directly attached AS 64496 and any longer AS paths 

Answer: C 

Explanation: 

If you want AS 1 to get networks originated from AS 4 and all directly attached ASs of AS 4, apply the following inbound filter on Router 1. ip as-path access-list 1 permit ^4_[0-9]*$ router bgp 1 neighbor 4.4.4.4 remote-as 4 neighbor 4.4.4.4 route-map foo in route-map foo permit 10 match as-path 1 In the ip as-path access-list command, the carat (^) starts the input string and designates "AS". The underscore (_) means there is a a null string in the string that follows "AS 4". The [0-9]* specifies that any connected AS with a valid AS number can pass the filter. The advantage of using the [0-9]* syntax is that it gives you the flexibility to add any number of ASs without modifying this command string. 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13754-26.html 


Q448. Which three factors does Cisco PfR use to calculate the best exit path? (Choose three.) 

A. quality of service 

B. packet size 

C. delay 

D. loss 

E. reachability 

F. administrative distance 

Answer: C,D,E 

Explanation: 

Cisco PfR selects an egress or ingress WAN path based on parameters that affect application performance, including reachability, delay, cost, jitter, and Mean Opinion Score (MOS). 

Reference: http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/performance-routing-pfr/product_data_sheet0900aecd806c4ee4.html 


Q449. What is a reason for 6PE to use two MPLS labels in the data plane instead of one? 

A. 6PE allows penultimate hop popping and has a requirement that all P routers do not have to be IPv6 aware. 

B. 6PE does not allow penultimate hop popping. 

C. It allows MPLS traffic engineering to work in a 6PE network. 

D. It allows 6PE to work in an MPLS network where 6VPE is also deployed. 

Answer: A 

Explanation: 

Q. Why does 6PE use two MPLS labels in the data plane? 

A. 6PE uses two labels: 

. The top label is the transport label, which is assigned hop-by-hop by the Label Distribution Protocol (LDP) or by MPLS traffic engineering (TE). 

. The bottom label is the label assigned by the Border Gateway Protocol (BGP) and advertised by the internal BGP (iBGP) between the Provider Edge (PE) routers. 

When the 6PE was released, a main requirement was that none of the MPLS core routers (the P routers) had to be IPv6-aware. That requirement drove the need for two labels in the data plane. There are two reasons why the 6PE needs both labels. 

PHP Functionality 

If only the transport label were used, and if penultimate hop popping (PHP) were used, the penultimate hop router (the P router) would need to understand IPv6. 

With PHP, this penultimate hop router would need to remove the MPLS label and forward the packet as an IPv6 packet. This P router would need to know that the packet is IPv6 because the P router would need to use the correct Layer 2 encapsulation type for IPv6. (The encapsulation type is different for IPv6 and IPv4; for example, for Ethernet, the encapsulation type is 0x86DD for IPv6, while it is 0x0800 for IPv4.) If the penultimate hop router is not IPv6-capable, it would likely put the Layer 2 encapsulation type for IPv4 for the IPv6 packet. The egress PE router would then believe that the packet was IPv4. There is time-to-live (TTL) processing in both the IPv4 and IPv6 headers. In IPv6, the field is called Hop Limit. The IPv4 and IPv6 fields are at different locations in the headers. Also, the Header Checksum in the IPv4 header would also need to be changed; there is no Header Checksum field in IPv6. If the penultimate hop router is not IPv6-capable, it would cause the IPv6 packet to be malformed since the router expects to find the TTL field and Header Checksum field in the header. Because of these differences, the penultimate hop router would need to know it is an IPv6 packet. How would this router know that the packet is an IPv6 packet, since it did not assign a label to the IPv6 Forwarding Equivalence Class (FEC), and there is no encapsulation field in the MPLS header? It could scan for the first nibble after the label stack and determine that the packet is IPv6 if the value is 6. However, that implies that the penultimate hop router needs to be IPv6-capable. This scenario could work if the explicit null label is used (hence no PHP). However, the decision was to require PHP. 

Load Balancing 

Typical load balancing on a P router follows this process. The P router goes to the end of the label stack and determines if it is an IPv4 packet by looking at the first nibble after the label stack. 

. If the nibble has a value of 4, the MPLS payload is an IPv4 packet, and the P router load balances by hashing the source and destination IPv4 addresses. 

. If the P router is IPv6-capable and the value of the nibble is 6, the P router load balances by hashing the source and destination IPv6 addresses. 

. If the P router is not IPv6-capable and the value of the nibble is not 4 (it could be 6 if the packet is an IPv6 packet), the P router determines it is not an IPv4 packet and makes the load balancing decision based on the bottom label. In the 6PE scenario, imagine there are two egress PE routers advertising one IPv6 prefix in BGP towards the ingress PE router. This IPv6 prefix would be advertised with two different labels in BGP. Hence, in the data plane, the bottom label would be either of the two labels. This would allow a P router to load balance on the bottom label on a per-flow basis. If 6PE used only the transport label to transport the 6PE packets through the MPLS core, the P routers would not be able to load balance these packets on a per-flow basis unless the P routers were IPv6-capable. If the P routers were IPv6-capable, they could use the source and destination IPv6 addresses in order to make a load balancing decision. 

Reference: http://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/116061-qa-6pe-00.html 


Q450. DRAG DROP 

Drag and drop the EIGRP term on the left to the corresponding definition on the right. 


Answer: