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<Some MPLS question>

Unanswered Question
Feb 20th, 2004
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I have trouble with those question, can you explain for me?


QUESTION NO: 1

You need VRF route to limit the effect of ______. (Choose two)

A. Route loops on the MPLS VPN backbone.

B. Malicious behavior on the MPLS VPN backbone.

C. Excessive hop count on the customer's network.

D. Configuration errors on the MPLS VPN backbone.


QUESTION NO: 2

Which statement is true about the hardware requirements of MPLS?

A. Because you do not need to run a routing protocol on P-routers, they require less

memory than routers supporting classic IP routing.

B. Because of the additional processing and memory requirements needed to build the

LFIB, MPLS is only available on high end routers.

C. MPLS is available on low end routers, built their use is limited because of the

additional processing and memory requirements needed to build the LFIB.

D. Because P-routers do not need to carry routes outside the MPLD domain, they

require less memory than routers that support the same application using classic IP

routing.


QUESTION NO: 3

When should you disable redistribution of IPv4 routing updates between MP-BGP

neighbors?

A. When the network only supports MPLS VPNs.

B. When the network is using OSPF or ISIS instead of I-BGP as the network IGP.

C. When you want to reduce the number of labels that the P-router needs to store.

D. When you want to reduce the number of routes that the P-routers must store in their

global BGP routing table.


QUESTION NO: 4

You should run frame-mode MPLS over an ATM network _______. (Choose two)

A. In situations where ATM SVCs are not available.

B. On low end routers that cannot support the number of virtual circuits needed to run cell

mode.

C. In situations where the labeled packets must traverse ATM networks that do not support

MPLS.

D. In a migration scenario where the network is moving a classic IP over ATM to an

MPLS aware ATM network.


QUESTION NO: 5

How does a PE-router operating in the default frame mode distribute labels?

A. The PE-router distributes a label for every destination in its FIB.

B. The PE-router only distributes labels for destinations inside the MPLS domain.

C. The PE-router only distributes labels for destinations outside the MPLS domain.

D. The PE-router does not distribute labels. Label distribution is only done by the core

LSR



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Harold Ritter Fri, 02/20/2004 - 04:30
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Q1: VRF route limit is usually used to limit the number of routes received from the customer. The answer should be B and D.


Q2: The answer should be D but very few people only run an IGP on the PE. They usually also run BGP.


Q3: Should be A. If there is only a need for VPN routes between two PEs, you can disable IPv4. This is kind of rare in a real life scenario.


Q4: C for sure. If the ATM network doesn't support MPLS then the only alternative is to run frame mode.

My other choice would be B.


Q5: The answer should be B. Label allocation and distribution is only done for internal routes (any routes other than BGP actually).


Hope this helps,

hungnt Fri, 02/20/2004 - 23:33
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Q1: in this question, I think that it don't mention to "route limit", It said that : ((("VRF route" to limit....))). So I not sure about this anwser.


Q5: I read in many books, it said that LSR routers always distribute label for all destination in "IP table" (and some book refer to LIB). and because in the IP table of LSR contain all routes regradless inside or outside MPLS domain ==> it distributes to all routes inside and out side MPLS domain. What I said here is not mention to "internet routing" or "VPN MPLS" it just for mormally for MPLS.


That my personnal idea

Harold Ritter Sat, 02/21/2004 - 05:35
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Q1: I certainly misread ;o) Now that I read it carefully, I don't even understand it.


Q5: I know for sure that Cisco IOS will not allocate and distribute labels for BGP learnt route (external routes) but only for IGP routes (dynamic or static).


Hope this helps,


Harold Ritter Sat, 02/21/2004 - 06:25
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About Q1, I believe that the question is poorly expressed and that is pertains to route limit. B and D still get my vote ;o)

mesuti Thu, 02/26/2004 - 00:35
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hritter,


I think that the correct answers in Q.3 are C and D,

that's what I read in MPLS and VPN Architectures


There are several benefits gained by running MPLS in Frame-mode across a WAN network:

• You can use the existing WAN infrastructure for transporting labeled packets.

• You can run MPLS across ATM networks that are not yet MPLS-enabled or across public ATM networks that do not support MPLS services.

• The migration of ATM networks toward MPLS becomes simple as the Frame-mode MPLS between routers offers a very convenient first transitional step.



I hope that you can help with 2 questions?


Can we say that SoO can be used as a loop prevention mechanism when redistributing routes from MP-BGP to OSPF?


When using MPLS on an MPLS aware ATM network, which two statements are true?(Choose two)

A. VPI and VCI are used as labels.

B. PVCs must be manually created between end devices.

C. The ATM devices become aware of Layer 3 by running a Layer 3 routing protocol.

D. When running BGP, it is no longer necessary to establish logical connection between

BGP neighbors.


A is for sure, as the second question I would choose B ( although that I think that B corresponds to Frame-mode MPLS rather than Cell-mode MPLS) because other questions doesn't look to be correct to me


Hope that you can help me!


Harold Ritter Thu, 02/26/2004 - 05:02
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About Q3, I think the wording is not to clear but it says:


When should you disable redistribution of IPv4 routing updates between MP-BGP

neighbors?


As I interpret it they want to know when you could disable address family IPv4 on the BGP session between the two PEs. Then the answer is clearly A.


First question:


Absolutely.


Second question:


A and C. The ATM device does need to become layer 3 aware when used in cell mode.


Hope this helps,


mesuti Thu, 02/26/2004 - 08:12
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dear hritter,


I meant about Q.4, but mistakenly wrote Q.3, I excuse.


QUESTION NO: 4

You should run frame-mode MPLS over an ATM network _______. (Choose two)

A. In situations where ATM SVCs are not available.

B. On low end routers that cannot support the number of virtual circuits needed to run cell

mode.

C. In situations where the labeled packets must traverse ATM networks that do not support

MPLS.

D. In a migration scenario where the network is moving a classic IP over ATM to an

MPLS aware ATM network?


In MPLS and VPN Architectures says:


There are several benefits gained by running MPLS in Frame-mode across a WAN network:

• You can use the existing WAN infrastructure for transporting labeled packets.

• You can run MPLS across ATM networks that are not yet MPLS-enabled or across public ATM networks that do not support MPLS services.

• The migration of ATM networks toward MPLS becomes simple as the Frame-mode MPLS between routers offers a very convenient first transitional step.


so can we say that the answers are C and D


once again thank you very much for your help

Harold Ritter Thu, 02/26/2004 - 20:48
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It is fair to say that C and D would be the correct answers.



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