Ensurepass

 

QUESTION 311

Which bit should be set in the link-state PDU of an IS-IS L1/L2 router to indicate that it is a potential exit point of the area?

 

A.	the ABR bit
B.	the ATT bit
C.	the down bit
D.	the P bit

 

Correct Answer: B

Explanation:

Default routing is achieved in two distinct ways with Integrated IS-IS:

 

Attached bit–Set by a Level 1/Level 2 router in its own Level 1 LSP and used to indicate to all Level 1 routers (within the area) that this router is a potential exit point of the area. Level 1-only routers will default to the nearest attached Level 2 router.

Default information originate–Can be configured in Level 1 as well as Level 2. The default route (0.0.0.0/0) is inserted in the router LSP (Level 1 or Level 2, according to the configuration command) and the LSP is flooded according to the router type (Level 1 or Level 2). A Level 2 router doesn’t need to have a default route to originate a default route.

 

Reference: http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800a3e6f.shtml

 

 

QUESTION 312

Which two options are benefits of EIGRP OTP? (Choose two.)

 

A.	It allows EIGRP routers to peer across a service provider without the service provider involvement.
B.	It allows the customer EIGRP domain to remain contiguous.
C.	It requires only minimal support from the service provider.
D.	It allows EIGRP neighbors to be discovered dynamically.
E.	It fully supports multicast traffic.
F.	It allows the administrator to use different autonomous system numbers per EIGRP domain.

 

Correct Answer: AB

Explanation:

EIGRP Over the Top (OTP) allows EIGRP routers to peer across a service provider infrastructure without the SP’s involvement. In fact with OTP, the provider won’t see customer routes at all. EIGRP OTP acts as a provider-independent overlay that transports customer data between the customer’s routers.

To the customer, the EIGRP domain is contiguous. A customer’s EIGRP router sits at the edge of the provider cloud, and peers with another EIGRP router a different location across the cloud.

Learned routes feature a next hop of the customer router — not the provider. Good news for service providers is that customers can deploy EIGRP OTP with their involvement.

Reference: http://ethancbanks.com/2013/08/01/an-overview-of-eigrp-over-the-top-otp/

 

 

QUESTION 313

DRAG DROP

Drag and drop the OSPFv3 LSA type on the left to the functionality it provides on the right.

 

 

Correct Answer:

 

 

QUESTION 314

DRAG DROP

Drag and drop the OSPF network type on the left to the correct category of timers on the right.

 

 

Correct Answer:

 

 

QUESTION 315

DRAG DROP

Drag and drop the BGP attribute on the left to the correct category on the right.

 

 

Correct Answer:

 

Explanation:

Well Known Mandatory Attribute

AS_Path

Origin

 

Well Known Discretionary Attribute

Local Preference

 

Optional Transitive

Community

 

 

Reference: http://www.deepsh.it/networking/BGP/bgp-attributes.png

 

 

QUESTION 316

Refer to the exhibit. NHRP registration is failing; what might be the problem?

 

 

A.	invalid IP addressing
B.	fragmentation
C.	incorrect NHRP mapping
D.	incorrect NHRP authentication

 

Correct Answer: D

Explanation:

Configuring an authentication string ensures that only routers configured with the same string can communicate using NHRP. Therefore, if the authentication scheme is to be used, the same string must be configured in all devices configured for NHRP on a fabric.

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_4/ip_addr/configuration/guide/hadnhrp.html#wp10554

 

 

QUESTION 317

In GETVPN, which key is used to secure the control plane?

 

A.	Traffic Encryption Key (TEK)
B.	content encryption key (CEK)
C.	message encryption key (MEK)
D.	Key Encryption Key (KEK).

 

Correct Answer: D

Explanation:

GDOI introduces two different encryption keys. One key secures the GET VPN control plane; the other key secures the data traffic. The key used to secure the control plane is commonly called the Key Encryption Key (KEK), and the key used to encrypt data traffic is known as Traffic Encryption Key (TEK).

Reference: Group Encrypted Transport VPN (Get VPN) Design and Implementation Guide PDF

 

 

QUESTION 318

Which statement is true comparing L2TPv3 to EoMPLS?

 

A.	L2TPv3 requires OSPF routing, whereas EoMPLS does not.
B.	EoMPLS requires BGP routing, whereas L2TPv3 does not.
C.	L2TPv3 carries L2 frames inside MPLS tagged packets, whereas EoMPLS carries L2 frames inside IPv4 packets.
D.	L2TPv3 carries L2 frames inside IPv4 packets, whereas EoMPLS carries L2 frames inside MPLS packets.

 

Correct Answer: D

Explanation:

Ethernet-over-MPLS (EoMPLS) provides a tunneling mechanism for Ethernet traffic through an MPLS-enabled L3 core and encapsulates Ethernet protocol data units (PDUs) inside MPLS packets (using label stacking) to forward them across the MPLS network. Another technology that more or less achieves the result of AToM is L2TPV3. In the case of L2TPV3 Layer 2 frames are encapsulated into an IP packet instead of a labelled MPLS packet.

Reference: http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-3/lxvpn/configuration/guide/lesc43xbook/lesc43p2ps.html

 

 

QUESTION 319

Which statement is true about VPLS?

 

A.	MPLS is not required for VPLS to work.
B.	VPLS carries packets as Layer 3 multicast.
C.	VPLS has been introduced to address some shortcomings of OTV.
D.	VPLS requires an MPLS network.

 

Correct Answer: D

Explanation:

VPLS uses MPLS labels so an MPLS network is required. VPLS MPLS packets have a two-label stack. The outer label is used for normal MPLS forwarding in the service provider’s network. If BGP is used to establish the VPLS, the inner label is allocated by a PE as part of a label block. If LDP is used, the inner label is a virtual circuit ID assigned by LDP when it first established a mesh between the participating PEs. Every PE keeps track of assigned inner label, and associates these with the VPLS instance.

Reference: http://en.wikipedia.org/wiki/Virtual_Private_LAN_Service

 

 

QUESTION 320

According to RFC 4577, OSPF for BGP/MPLS IP VPNs, when must the down bit be set?

 

A.	when an OSPF route is distributed from the PE to the CE, for Type 3 LSAs
B.	when an OSPF route is distributed from the PE to the CE, for Type 5 LSAs
C.	when an OSPF route is distributed from the PE to the CE, for Type 3 and Type 5 LSAs
D.	when an OSPF route is distributed from the PE to the CE, for all types of LSAs

 

Correct Answer: C

Explanation:

If an OSPF route is advertised from a PE router into an OSPF area, the Down bit (DN) is set. Another PE router in the same area does not redistribute this route into iBGP of the MPLS VPN network if down is set.

RFC 4577 says:

“When a type 3 LSA is sent from a PE router to a CE router, the DN bit 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.”

For more information about Down bit according to RFC 4577 please read more here.

http://tools.ietf.org/html/rfc4577#section-4.2.5.1.

 

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