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Q81. Refer to the exhibit. 

Which statement is true about the downward bit? 

A. It forces the CE router to use a backup link instead of sending traffic via MPLS VPN. 

B. It informs the PE router that the LSA metric has been recently decreased to 1 and that partial SPF calculation cannot be delayed. 

C. It forces the CE router to install the LSA with the downward bit set into its routing table as a discard route. 

D. It informs the PE router that the LSA was already redistributed into BGP by another PE router and that the LSA must not be redistributed into BGP again. 

Answer:

Explanation: 

From RFC 4577, specifically section 4.2.5.1 

When a type 3 LSA is sent from a PE router to a CE router, the DN bit [OSPF-DN] in the LSA Options field MUST be set. This is used to ensure that if any CE router sends this type 3 LSA to a PE router, the PE router will not redistribute it further. 

When a PE router needs to distribute to a CE router a route that comes from a site outside the latter’s OSPF domain, the PE router presents itself as an ASBR (Autonomous System Border Router), and distributes the route in a type 5 LSA. The DN bit [OSPF-DN] MUST be set in these LSAs to ensure that they will be ignored by any other PE routers that receive them. 


Q82. Which two improvements do SIA-Query and SIA-Reply messages add to EIGRP? (Choose two.) 

A. Stuck-in-active conditions are solved faster. 

B. They prevent a route from going into the stuck-in-active state. 

C. They help in the localization of the real failure in the network. 

D. The EIGRP adjacency between two neighbors never goes down. 

Answer: A,C 


Q83. Which two statements about IS-IS are true? (Choose two.) 

A. The default hello interval is 10 seconds and the default hold timer is 30 seconds. 

B. The hello interval can be changed on a per-interface basis with the command isis hello-multiplier. 

C. Both routers need to have the same hello intervals and hold timers in order to form IS-IS neighbors. 

D. Both IS-IS routers need to have the same capabilities in the hello packet in order to form neighbors. 

Answer: A,B 

Explanation: 

isis hello-interval 

To specify the length of time between hello packets that the Cisco IOS software sends, use the isis hello-interval command in interface configuration mode. By default, a value three times the hello interval seconds is advertised as the hold time in the hello packets sent. (Change the multiplier of 3 by specifying the isis hello-multiplier command.) With smaller hello intervals, topological changes are detected faster, but there is more routing traffic. The default is 10 seconds. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfisis.ht ml 


Q84. When the BGP additional-paths feature is used, what allows a BGP speaker to differentiate between the different available paths? 

A. The remote BGP peer prepends its own next-hop address to the prefix. 

B. A unique path identifier is encoded into a dedicated field to the NLRI. 

C. A route distinguisher is appended to the prefix by the receiving BGP speaker. 

D. The additional path information is encoded in an extended community. 

Answer:


Q85. Which three statements are true about OSPFv3? (Choose three.) 

A. The only method to enable OSPFv3 on an interface is via the interface configuration mode. 

B. Multiple instances of OSPFv3 can be enabled on a single link. 

C. There are two methods to enable OSPFv3 on an interface, either via the interface configuration mode or via the router configuration mode. 

D. For OSPFv3 to function, IPv6 unicast routing must be enabled. 

E. For OSPFv3 to function, IPv6 must be enabled on the interface. 

F. Only one instance of OSPFv3 can be enabled on a single link. 

Answer: B,D,E 

Explanation: 

Here is a list of the differences between OSPFv2 and OSPFv3: 

They use different address families (OSPFv2 is for IPv4-only, OSPFv3 can be used for IPv6-only or both protocols (more on this following)) 

OSPFv3 introduces new LSA types 

OSPFv3 has different packet format 

OSPFv3 uses different flooding scope bits (U/S2/S1) 

OSPFv3 adjacencies are formed over link-local IPv6 communications 

OSPFv3 runs per-link rather than per-subnet 

OSPFv3 supports multiple instances on a single link, Interfaces can have multiple IPv6 addresses 

OSPFv3 uses multicast addresses FF02::5 (all OSPF routers), FF02::6 (all OSPF DRs) 

OSPFv3 Neighbor Authentication done with IPsec (AH) 

OSPFv2 Router ID (RID) must be manually configured, still a 32-bit number 

Following is a simple example of OSPFv3 configuration on a Cisco IOS 12.4T router. 

ipv6 unicast-routing 

ipv6 cef 

interface GigabitEthernet 0/0 

description Area 0.0.0.0 backbone interface 

ipv6 address 2001:DB8:100:1::1/64 

ipv6 ospf network broadcast 

ipv6 ospf 100 area 0.0.0.0 

Reference: http://www.networkworld.com/article/2225270/cisco-subnet/ospfv3-for-ipv4-and-ipv6.html 


Q86. Which two statements are true about IS-IS? (Choose two.) 

A. IS-IS DIS election is nondeterministic. 

B. IS-IS SPF calculation is performed in three phases. 

C. IS-IS works over the data link layer, which does not provide for fragmentation and reassembly. 

D. IS-IS can never be routed beyond the immediate next hop. 

Answer: C,D 

Explanation: 

IS-IS runs directly over the data link alongside IP. On Ethernet, IS-IS packets are always 802.3 frames, with LSAPs 0xFEFE while IP packets are either Ethernet II frames or SNAP frames identified with the protocol number 0x800. OSPF runs over IP as protocol number 89. 

IS-IS runs directly over layer 2 and hence: 

-cannot support virtual links unless some explicit tunneling is implemented 

-packets are kept small so that they don't require hop-by-hop fragmentation 

-uses ATM/SNAP encapsulation on ATM but there are hacks to make it use VcMux encapsulation 

-some operating systems that support IP networking have been implemented to differentiate Layer 3 packets in kernel. Such Oss require a lot of kernel modifications to support IS-IS for IP routing. 

-can never be routed beyond the immediate next hop and hence shielded from IP spoofing and similar Denial of Service attacks. 

Reference: https://tools.ietf.org/html/draft-bhatia-manral-diff-isis-ospf-00 


Q87. Refer to the exhibit. 

If a console port is configured as shown, which response is displayed when you connect to the console port? 

A. a blinking cursor 

B. the message "Authorized users only" 

C. the username prompt 

D. three username name prompts followed by a timeout message 

E. the message "Connection refused" 

Answer:


Q88. DRAG DROP 

Drag and drop the argument of the mls ip cef load-sharing command on the left to the function it performs on the right. 

Answer: 


Q89. What does a nonzero forwarding address indicate in a type-5 LSA? 

A. It indicates that this link-state ID is eligible for ECMP. 

B. It indicates that this router should have an OSPF neighbor relationship with the forwarding address before using this link-state ID. 

C. It indicates that the receiving router must check that the next hop is reachable in its routing table before using this link-state ID. 

D. It indicates that traffic can be directly routed to this next hop in shared segment scenarios where the external route source is directly connected. 

Answer:

Explanation: 

The value of the forwarding address specified by the autonomous system boundary router (ASBR) can be either 0.0.0.0 or non-zero. The 0.0.0.0 address indicates that the originating router (the ASBR) is the next hop. The forwarding address is determined by these conditions: 

. The forwarding address is set to 0.0.0.0 if the ASBR redistributes routes and OSPF is not enabled on the next hop interface for those routes. 

. These conditions set the forwarding address field to a non-zero address: ASBR's next hop interface address falls under the network range specified in the router ospf command. 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13682-10.html 


Q90. Which statement about the OSPF Loop-Free Alternate feature is true? 

A. It is supported on routers that are configured with virtual links. 

B. It is supported in VRF OSPF instances. 

C. It is supported when a traffic engineering tunnel interface is protected. 

D. It is supported when traffic can be redirected to a primary neighbor. 

Answer:

Explanation: 

Restrictions for OSPF IPv4 Remote Loop-Free Alternate IP Fast Reroute 

. The OSPF IPv4 Remote Loop-Free Alternate IP Fast Reroute feature is not supported on devices that are virtual links headends. 

. The feature is supported only in global VPN routing and forwarding (VRF) OSPF 

Instances. 

. The only supported tunneling method is MPLS. 

. You cannot configure a traffic engineering (TE) tunnel interface as a protected interface. Use the MPLS Traffic Engineering—Fast Reroute Link and Node Protection feature to protect these tunnels. For more information, see the “MPLS Traffic Engineering—Fast Reroute Link and Node Protection” section in the Multiprotocol Label Switching Configuration Guide. 

. You can configure a TE tunnel interface in a repair path, but OSPF will not verify the tunnel’s placement; you must ensure that it is not crossing the physical interface that it is intended to protect. 

. Not all routes can have repair paths. Multipath primary routes might have repair paths for all, some, or no primary paths, depending on the network topology, the connectivity of the computing router, and the attributes required of repair paths. 

. Devices that can be selected as tunnel termination points must have a /32 address advertised in the area in which remote LFA is enabled. This address will be used as a tunnel termination IP. If the device does not advertise a /32 address, it may not be used for remote LFA tunnel termination. 

. All devices in the network that can be selected as tunnel termination points must be configured to accept targeted LDP sessions using the mpls ldp discovery targeted-hello accept command. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-3s/iro-xe-3s-book/iro-ipfrr-lfa.html