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October 12th, 2012 1 comment

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Share your SPADVROUTE Experience

October 12th, 2012 443 comments

Please share with us your experience after taking the SPADVROUTE 642-885 exam, your materials, the way you learned, your recommendations…

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Share your SPROUTE Experience

October 12th, 2012 214 comments

Please share with us your experience after taking the SPROUTE 642-883 exam, your materials, the way you learned, your recommendations…

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Share your SPEDGE Experience

October 12th, 2012 492 comments

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Share your SPCORE Experience

October 12th, 2012 411 comments

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MPLS VPN Lab Sim

May 29th, 2011 10 comments

The Indigo IT Company is a banking service that is using EIGRP AS 1 as the IGP in its network.Indigo IT Company has decided to establish connectivity between two of its sites. AdvanceNet, a service provider, has been selected by the Indigo IT Company to provide the connectivity between the two sites.

For this implementation, AdvanceNet is using a MPLS VPN solution. AdvanceNet has already established MPLS connectivity between all of their PE routers. MPBGP connectivity has also been established on all PE routers.

Indigo IT Company has successful completed all necessary tasks on the CE routers, and AdvanceNet has successfully completed all necessary MPLS VPN configuration tasks on PE12.

MPLS_VPN_topology.jpgYour task is to successfully complete the implementation of the VPN connection by configuring the MPLS VPN on PE11 using the following information:
Privileged mode password: *********
EIGRP is to be used the PE-CE protocol for the VPN.
MPBGP is being used to propagate VPN routing information between the PE routers.
The interface supporting the Indigo Company is Serial0/0 and will have an IP address
of 150.1.244.18 255.255.255.240.

The following has been assigned to Indigo’s VPN:
The VRF name is Customer_6
The RD is 6:10
The route target for import is 14:10.
The route target for export is 14:10.
Configure EIGRP between CE11A and PE11 using AS number 10.
Redistribute from BGP to EIGRP AS 10 using metric string of 10000 100 255 11500.
Redistribute from EIGRP AS 10 to BGP using a metric of 1.
VPN is operational when you can see routes for both the local (10.1.11.10) and the remote (10.1.12.0) sites in the VRF routing table

Answer and Explanation

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Share your BGP Experience

May 17th, 2011 192 comments

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Share your MPLS Experience

May 17th, 2011 129 comments

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Basic MPLS VPN VRF GNS3 Lab

May 9th, 2011 11 comments

Virtual Routing and Forwarding Table (VRF) allows to create multiple routing tables within a single router. Each of them is assigned to a customer; therefore customers can use the same IP (even private IP) with other customers without confusing the PE router.

GNS3_MPLS_VPN_VRF_topology.jpg

In the above example, R0 is the Provider Edge (PE) router which is on the ISP side while R1 and R2 are customer routers (CustomerA and CustomerB respectively).

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Basic MPLS Tutorial

May 4th, 2011 30 comments

MPLS is a new forwarding mechanism called “label switching” in which packets are forwarded based on labels. However, hosts are unaware about labeled packets so routers will need to add a label when entering “MPLS area” and remove that label after leaving there.

The idea of label switching is to have only the first router do an IP lookup and assign a label, then all future routes in the network can “cheat” by doing exact match “switching” based on a label. This would reduce load on the core routers, where high-performance was the most difficult to achieve, and distribute the routing lookups across lower speed edge routers.

In a traditional IP network:
* Each router performs an IP lookup (“routing”), determines a next-hop based on its routing table, and forwards the packet to that next-hop.
* Rinse and repeat for every router, each making its own independent routing decisions, until the final destination is reached.
MPLS does “label switching” instead:
* The first device does a routing lookup, just like before.
* But instead of finding a next-hop, it finds the final destination router.
* And it finds a pre-determined path from “here” to that final router.
* The router applies a “label” (or “shim”) based on this information.
* Future routers use the label to route the traffic without needing to perform any additional IP lookups.
* At the final destination router, the label is removed and the packet is delivered via normal IP routing.

Therefore in an MPLS network, data packets are assigned labels. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself.

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MPLS Fundamentals

April 15th, 2011 15 comments

Here you will find answers to MPLS Fundamentals Questions

Question 1

What is a benefit of CEF switching?

A. CEF supports IP source prefix-based switching using the FIB.
B. CEF uses less memory than fast switching uses.
C. CEF is less CPU intensive than fast switching is.
D. CEF provides Netflow statistics with minimum CPU overhead.
E. CEF allows multiple data planes to share a common control plane.

 

Answer: C

Explanation

CEF offers the following benefits:
* Improved performance – CEF is less CPU-intensive than fast switching route caching. More CPU processing power can be dedicated to Layer 3 services such as quality of service (QoS) and encryption.
* Scalability – CEF offers full switching capacity at each line card when distributed CEF (dCEF) mode is active.
* Resilience – CEF offers unprecedented level of switching consistency and stability in large dynamic networks. In dynamic networks, fast switching cache entries are frequently invalidated due to routing changes. These changes can cause traffic to be process switched using the routing table, rather than fast switched using the route cache. Because the Forwarding Information Base (FIB) lookup table contains all known routes that exist in the routing table, it eliminates route cache maintenance and the fast switch/process switch forwarding scenario. CEF can switch traffic more efficiently than typical demand caching schemes.

(Reference: http://www.cisco.com/en/US/docs/ios/12_1/switch/configuration/guide/xcdcef.html)

Question 2

What are two concerns when implementing CEF switching? (Choose two)

A. increased CPU utilization from maintaining the FIB table
B. increased memory requirement
C. the requirement to disable other IOS features such as NBAR and MQC
D. increased memory requirement on the VIP when implementing DCEF
E. configuration complexity
F. troubleshooting complexity because of the many tables that CEF maintains

 

Answer: B D

Explanation

If the router contains too many routing (for example 100,000 networks), enabling the CEF may consume excessive memory. Enabling the distributed CEF will also affect memory utilization on Versatile Interface Processor (VIP) modules or line cards, because the entire FIB table will be copied to all VIP modules or line cards.

Question 3

Using MPLS unicast IP forwarding, what will happen if an LSR receives an unlabeled incoming packet?

A. It will process switch the packet by doing a routing table lookup.
B. It will forward the packet using the LFIB.
C. It will forward the packet using the LIB.
D. It will forward the packet using the FIB.
E. It will drop the packet immediately.

 

Answer: D

Explanation

The FIB (in the data plane) is the database used to forward unlabeled IP packets. A forwarded packet is labeled if a next-hop label is available for a specific destination IP network. Otherwise, a forwarded packet is not labeled.

Note:

The LIB (in the control plane) is the database used by Label Distribution Protocol (LDP) where an IP prefix is assigned a locally significant label that is mapped to a next-hop label that has been learned from a downstream neighbor.

The LFIB (in the data plane) is the database used to forward labeled packets. Local labels, previously advertised to upstream neighbors, are mapped to next-hop labels, previously received from downstream neighbors.

Question 4

When using MPLS unicast IP forwarding, what will happen if an LSR receives an incoming labeled packet but the LSR can’t find that incoming label in its LFIB?

A. The packet will be forwarded using the FIB.
B. The packet will be forwarded using the LIB.
C. The packet will be process switched by performing a route lookup in the routing table.
D. The packet will be forwarded using the LFIB with an imp-null outgoing label.
E. The packet will be dropped even if the IP destination exists in the FIB.

 

Answer: E

Question 5

Which three fields must be included in MP-BGP updates between PE routers in an MPLS network? (Choose three)

A. VPNv4 address
B. label used for VPN packet forwarding
C. AS path
D. Site of Origin
E. TE path designator

Answer: A B C

Explanation

An MP-BGP update contains these elements:

  • VPNv4 address
  • Extended communities (route targets, optionally SOO)
  • Label used for VPN packet forwarding
  • Any other BGP attribute (for example, AS path, local preference, MED, standard community)

An MP-BGP update exchange between PE routers contains these elements:

  • VPNv4 address
  • Extended BGP communities (route targets [RTs] are required; Site of Origin [SOO] is optional)
  • Label used for VPN packet forwarding

Question 6

Which three statements correctly describe how labels are used in cell-mode MPLS? (Choose three)

A. The ATM header VPI/VCI field is used for forwarding decisions.
B. The 32-bit MPLS label is preserved in the frame but is not used in the ATM network.
C. The original MPLS label is present only in the first cell of a packet.
D. The 32-bit MPLS label is inserted between the ATM header and the ATM AAL5 header.
E. Labels in cell-mode MPLS are not a scarce resource like in frame-mode MPLS.
F. The TTL field in the MPLS label is copied into the ATM header TTL field by the ingress edge LSR.

 

Answer: A B C

Explanation

Cell-mode MPLS is MPLS using ATM Layer 2 encapsulation, where the ATM switch is participating as an LSR. In cell-mode MPLS, a label cannot be inserted on every cell; therefore, the virtual path identifier/virtual channel identifier (VPI/VCI) fields in the ATM header are used as a label.

Cell-mode MPLS uses the ATM header’s VPI/VCI field for forwarding decisions while the 32-bit label is still preserved in the frame but not used in the ATM network. The original label is only present in the first cell of a packet.

MPLS_Frame_mode_Cell_mode.jpg

Question 7

Refer to the exhibit. It shows an MPLS network with four routers as well as two customer routers. Router E is advertising the network 192.168.12.0/24. Rather than propagating the 192.168.12.0/24 network, Router D aggregates the 192.168.12.0/24 route into 192.16.0.0/16. Which route or routes will Router B receive?

MPLS_path_selection.jpgA. only 192.168.0.0/16
B. only 192.160.12.0/24
C. both 192.168.0.0/16 and 192.160.12.0/24
D. neither of the routes-the LSP is broken

 

Answer: A

Question 8

Refer to the exhibit. A diagram of a router connected to an MPLS-enabled ATM switch via an LC-ATM MPLS interface, and a partial configuration for the MPLS-enabled ATM switch and router are shown. Which statement describes what is incorrect about the configuration shown?

MPLS_ATM.jpg

A. CEF has not been enabled on the router.
B. The VPI range of 2-3 is invalid.
C. The control VPI/VCI has not been set to 0/32 on the router.
D. VC-merge has not been enabled on the ATM switch interface.
E. The router has not been configured to specifically use LDP.

 

Answer: A

Question 9

Refer to the exhibit. A router connected to an MPLS-enabled ATM switch via an LC-ATM MPLS interface, and a partial configuration for the MPLS-enabled ATM switch and the router are shown. Which statement describes what is incorrect about the configurations shown?

MPLS_ATM_subinterface.jpg

A. The router subinterface is not specified as an MPLS cell-mode subinterface.
B. CEF has not been enabled on the ATM interface of the MPLS-enabled ATM switch.
C. The control VPI/VCI has not been set to 0/32.
D. VC-merge has not been enabled on the ATM interface of the MPLS-enabled ATM switch.
E. The router has not been configured to specifically use LDP.
F. The ATM interface of the MPLS-enabled ATM switch has not been configured for cell-mode MPLS operations.

 

Answer: A

Categories: BGP + MPLS 642-691 Exam Tags:

MPLS LDP TDP Questions

April 14th, 2011 4 comments

Here you will find answers to MPLS LDP Questions

Question 1

For which purpose is the command mpls ldp maxhops used?

A. In large ATM-MPLS networks, the LFIB can become too large and it may be necessary to limit the maximum diameter of the MPLS LSPs.
B. Because downstream-on-demand label allocation uses hop count to control loop detection, it maybe necessary to limit the maximum diameter of the MPLS network.
C. Because end-to-end delay can cause problems with some voice applications, it may be necessary to limit the maximum diameter of the MPLS network.
D. When interconnecting large frame mode MPLS and cell mode networks it may be necessary to limit the maximum network diameter to prevent forwarding loops.

 

Answer: B

Explanation

The “mpls ldp maxhops” command is used to limit the number of hops permitted in a label switched path (LSP) established by the Downstream on Demand (DoD) method of label distribution.

Note: When the downstream-on-demand method is used, an LSR advertises its locally assigned (incoming) labels to its LDP peer only when the peer requests them.

Question 2

Which two of the following statements regarding LDP are true? (Choose two)

A. LDP can also be used between nonadjacent routers using multicast LDP hello messages.
B. LDP does not require periodic hello messages once the LDP session has been established between the LDP peers.
C. LDP hello messages use TCP packets with a destination port number of 646.
D. Multiple sessions can be established between a pair of LSRs if they use multiple label spaces.
E. Per-platform label space can be identified by a label space ID of 0 in the LDP identifier field.

 

Answer: D E

Question 3

Refer to the exhibit. Based on the show outputs, which condition could be preventing the P1 router from establishing TDP adjacency with its neighbor over the s0/0.211 and s0/0.212 subinterfaces?

P1#sh mpls ldp neighbor

P1#sh mpls interfaces

Interfaces IP Tunnel Operational
Serial0/0.211 Yes (tdp) No Yes
Serial0/0.212 Yes (tdp) No Yes

A. The s0/0.211 and s0/0.212 subinterfaces line protocol are in the down state.
B. The P1 router cannot establish a TCP session with its neighbors.
C. The P1 router is missing the mpls label protocol LDP command.
D. The show mpls tdp neighbor command needs to be used to view the TDP neighbor status.

 

Answer: B

Explanation

A is not correct as both of the serial interfaces are up (operational). If the “Operational” state is “yes”, labeled packets can be sent over this interface. It means that an MPLS protocol is configured on the interface and the required Layer 2
negotiations have occurred.

C is not correct as P1 router uses TDP (a label distribution protocol), not LDP.

D is not correct because the “show mpls tdp neighbor” command can be used to view the status of both TDP and LDP neighbor status.

Some information about neighbor establishment between two LDP/TDP routers:

LDP periodically sends hello messages (every 5 seconds). If the label switch router (LSR) is adjacent or one hop from its neighbor, the LSR sends out LDP link hello messages to all the routers on the subnet as User Datagram Protocol (UDP) packets with a multicast destination address of 224.0.0.2 (“all routers on a subnet”) and destination port number of 646 (TDP uses destination port 711) .

After discovering any LDP neighbor using multicast UDP hello messages, a TCP session must be established for LDP to exchange labels over a reliable connection. If the TCP session cannot be established between two routers (for example there is an access-list that denies TCP sessions on the well-known port number 711 TDP), they cannot become neighbors. And you will see an empty output when using the “show mpls ldp neighbor” command.

(Reference: MPLS Student Guide)

Categories: BGP + MPLS 642-691 Exam Tags:

MPLS VPN Questions

April 13th, 2011 22 comments

Here you will find answers to MPLS VPN Questions – Part 1

Question 1

Refer to the diagram. What problem can be caused by the second P router summarizing the loopback address of the egress PE router?

MPLS_summary_VPN.jpg

A. The first P router will be faced with a VPN label which it does not understand.
B. The second P router will be faced with a VPN label which it does not understand.
C. The egress PE router will not be able to establish a label switch path (LSP) to the ingress PE router.
D. A label switch path (LSP) will be established from the ingress PE router to the egress PE router, an event that is not desirable.
E. The ingress PE router will not be able to receive the VPN label from the egress PE router via MP-IBGP.

 

Answer: B

Explanation

When running MPLS VPN, there is a feature called penultimate hop popping (PHP). The “penultimate hop” is not the last LSR to process a labeled packet but the second-to-last LSR to process a labeled packet (which means the nearest router to the egress LSR). With this feature, the egress LSR does not have to perform two label lookups as PHP causes the penultimate hop to pop the MPLS label; leaving only VPN label for the egress LSR to proceed.

In this question, if the second P router summarizes the loopback IP address of the egress PE router then the Label Switch Path (LSP) tunnel will be broken.To understand why, let’s assume that the loopback address of the egress PE is 1.1.1.1/32 and the second P router summaries it as 1.1.0.0/16. The second P router has both networks in the routing table as below:
+ 1.1.1.1/32 (the original network)
+ 1.1.0.0/16 (the summary network)

The second P router only sends the summary network 1.1.0.0/16 to the first P router and ingress PE router. Also, the second P router thinks it is the last hop of the summary network 1.1.0.0/16 (because other routers don’t have information about this summary network) so it sends a pop label for this network to “First P router”. It also sends a label (7, for example) for the original netwok 1.1.1.1/32 to “First P router”.

MPLS_summary_VPN_explain.jpg

As the “Second P router” only sends summary network 1.1.0.0/16, “First P router” will understand that it needs to pop (remove) the label destined for this network, according to the PHP feature. It then sends this packet to the “second P router”. Therefore the “second P router” will get a VPN label which it cannot understand and the packet will be dropped.

Notice that in MPLS VPN, the next-hop label mapping to the downstream PE router’s loopback is used to forward the packet through the MPLS domain so the loopback address of the egress PE router is very important.

Some other useful information about MPLS VPN:

The VPN label of the BGP route is recognized only by the egress PE router, and will not be understood by any other router (core routers). At the egress PE router, that prefix  is associated with an outgoing interface belonging to a specific VRF on the router depending on the value in the VPN label. The VPN label is never touched until it reaches the egress PE router.

Aggregation should not be used where end-to-end LSPs are required, such as with:
– MPLS VPNs
– MPLS TEs
– MPLS-enabled ATM network
– Transit BGP where core routers are not running BGP

Question 2

On a dedicated subinterface implementation, PE-2 must establish an address-family vrf IPv4 BGP neighbor relationship with which router?

Internet Access Through a Dedicated Subinterface

MPLS_vrf_ipv4.jpg

A. CE-1
B. CE-2
C. PE-1
D. PE-IG
E. CE-1 and CE-2
F. PE-1 and PE-IG

 

Answer: B

Explanation

PE router needs to learn IP prefix from customer edge (CE) router so it must establish neighbor relationship with CE. The IP prefix is a member of IPv4 address family. After learning it, the PE converts it into a VPN-IPv4 prefix which is a member of VPN-IPv4 address family. It specifies the customer address uniquely even if the customer site uses private IP address.

Note:

You always have to configure a BGP address family for each VRF and configure route redistribution into BGP for each VRF, even if you do not use BGP as the PE-CE routing protocol.

(Reference: MPLS Student Guide)

Question 3

What are three drawbacks of a peer-to-peer VPN using a shared provider edge (PE) router? (Choose three)

A. A full mesh of virtual circuits is required between the customer sites.
B. All the customers have to share a common IP address space.
C. Optimal routing between customer sites cannot be guaranteed.
D. The shared PE router has to know all routes for all customers.
E. Packet filters are required on the PE routers.

 

Answer: B D E

Question 4

What is the difference in implementation between a managed CE services MPLS VPN and a central services MPLS VPN?

A. RD assignment
B. selective routes export
C. selective routes import
D. MP-BGP route redistribution filtering
E. CE-PE routing process
F. none

 

Answer: B

Question 5

What benefit does AToM provide to the service provider’s customers?

A. By supporting Layer 2 VPNs, customers maintain control of their site-to-site routings over the WAN.
B. By supporting Layer 3 VPNs, a full mesh of virtual circuits will not be required between the different customer sites to enable optimal routing. 
C. By supporting secured Layer 3 VPNs, customers do not have to deal with the complexity of configuring IPSec. 
D. By supporting MPLS traffic engineering over ATM, customers can better utilize their WAN link. 
E. By supporting Diff-Serv QoS, ATOM allows customers to deploy voice/video applications across the WAN.

 

Answer: A

Question 6

What is the purpose of the global configuration command, ip dhcp relay information option vpn?

A. enables the DHCP relay agent to insert the VPN suboptions to the BOOTP request
B. enables the DHCP relay agent to convert the broadcast DHCP request to a unicast DHCP request to a shared DHCP server 
C. enables the DHCP relay agent to perform VRF-aware NAT before forwarding the DHCP request to a shared DHCP server 
D. enables ODAP (On-Demand Address Pool) on the DHCP relay agent

 

Answer: A

Question 7

With MPLS VPN-aware NAT, what additional information is tracked inside the NAT translation table?

A. RD information 
B. RT information 
C. VRF information 
D. Multi-protocol BGP prefixes 
E. MPLS Labels

 

Answer: C

Question 8

Which of the following could be called a VPN identifier in the MPLS/VPN architecture?

A. route target 
B. route distinguisher 
C. VRF
D. VPN IPv4 address
E. BGP site-of-origin (SOO) extended community attribute

 

Answer: A

Explanation

The Route Distinguisher (RD) number is used to prefix the IP addresses for the site. This gives us a way to distinguish duplicate private addresses. For example, subnet 10.1.1.0 for VPN 16 is different than subnet 10.1.1.0 for VPN 20. From the MPLS VPN provider’s point of view they are 16:10.1.1.0 and 20:10.1.1.0, which are different. The RD is configured on the interface (or subinterface) connecting to the site.

But the RD cannot indicate that a site participates in more than one VPN. Therefore, route target (RT) were introduced in the MPLS VPN architecture to support complex VPN topologies. The RT indicates the VPN membership of a route and allows VPN routes to be imported or exported into or out of your VRFs. Similar to RDs, the RTs can be specified in one of these two formats:
* 16-bit AS number followed by a 32-bit decimal number (ASN:nn). For example, 15:3
* 32-bit IP address followed by a 16-bit decimal number (A.B.C.D:nn). For example, 172.16.23.45:10

Notice that while a particular prefix can have only one RD, that same prefix can have one or more RTs assigned to it.

Note: The route target can be considered a VPN identifier but route target is the closest approximation to a VPN identifier in the MPLS/VPN architecture.

Question 9

MPLS_VPN_neighbor.jpgRefer to the exhibit. The MPLS VPN Customer A is using a separate interface for Internet access. However, with the current configurations shown, the CE router is not receiving any Internet routes from the PE router. Which two additional configuration commands can resolve the Internet connectivity issue? (Choose two)

A. At the CE router, under router bgp 50101, add the neighbor 10.1.1.66 remote-as 50102 command.
B. At the CE router, under router bgp 50101, add the network 0.0.0.0 command.
C. At the CE router, under router bgp 50101, add the ip route 0.0.0.0 0.0.0.0 10.1.1.66 command.
D. At the PE router, under address-family ipv4 vrf Customer_A, add the neighbor 10.1.1.65 remote-as 50101 command.
E. At the PE router, under address-family ipv4 vrf Customer_A, add the neighbor 10.1.1.17 default-originate command.
F. At the PE router, under router bgp 50102, add the neighbor 10.1.1.65 remote-as 50101 command

 

Answer: A F

Question 10

Refer to the exhibit and the following connectivity requirements. How many different VRFs are required?

MPLS_VRF.jpgSites CE1A, CE1B, CE1C, and CE1D require connectivity among them.
Sites CE2A and CE2B require connectivity between them.
Site CE12A requires connectivity to sites CE1A, CE1B, CE1C, CE1D, and CE12B.
Site CE12B requires connectivity to sites CE2A, CE2B, and CE12A.

A. 2 VRFs 
B. 3 VRFs 
C. 4 VRFs 
D. 6 VRFs 
E. 8 VRFs 
F. 10 VRFs

 

Answer: C

Categories: BGP + MPLS 642-691 Exam Tags:

MPLS Basic Terminologies

April 13th, 2011 1 comment

* AS – autonomous system. A collection of networks that share the same routing protocol and that are under the same system administration.

*ASBR – autonomous system boundary router. A router that connects and exchanges information between two or more autonomous systems.

* BGP – Border Gateway Protocol. The exterior border gateway protocol used to exchange routing information between routers in separate autonomous systems. BGP uses Transmission Control Protocol (TCP). Because TCP is a reliable protocol, BGP does not experience problems with dropped or fragmented data packets.

* CE router – customer edge router. The customer router that connects to the provider edge (PE) router.

* eBGP – External Border Gateway Protocol. A BGP session between routers in different autonomous systems (ASs). When a pair of routers in different ASs are more than one IP hop away from each other, an EBGP session between those two routers is called multihop EBGP.

* iBGP – Internal Border Gateway Protocol. A BGP session between routers within the same autonomous system.

* IGP – Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).

* LDP—Label Distribution Protocol. A standard protocol between MPLS-enabled routers to negotiate the labels (addresses) used to forward packets. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).

* LER – label edge router. The edge router that performs label imposition and disposition.

* LSR – label switch router. The role of an LSR is to forward packets in an MPLS network by looking only at the fixed-length label.

* NLRI – Network Layer Reachability Information. BGP sends routing update messages containing NLRI, which describes the route. In this context, an NLRI is a prefix. A BGP update message carries one or more NLRI prefixes and the attributes of a route for the NLRI prefixes. The route attributes include a BGP next hop gateway address, community values, and other information.

* P router – provider router. The core router in the service provider network that connects to provider edge (PE) routers. In a packet-switched star topology, a router that is part of the backbone and that serves as the single pipe through which all traffic from peripheral networks must pass on its way to other peripheral networks.

* PE router – provider edge router. The label edge router (LER) in the service provider network that connects to the customer edge (CE) router.

* RR – route reflector. A router that advertises or reflects IBGP learned routes to other IBGP peers without requiring a full network mesh.

* VPN – Virtual Private Network. A group of sites that, as a result of a set of administrative policies, can communicate with each other over a shared backbone.

* VPNv4 addresses – When multiple VPNs use the same address space, the VPN addresses are made unique by adding a route distinguisher to the front of the address.

Categories: MPLS Knowledge Tags:

MPLS VPN Questions 2

April 12th, 2011 5 comments

Here you will find answers to MPLS VPN Questions – Part 2

Question 1

When configuring Internet access from a MPLS VPN using a separate subinterface, which two configurations are required on the PE router? (Choose two)

A. Use the ip vrf forwarding command on the subinterface that is used for MPLS VPN access.
B. Use the ip vrf forwarding command on the subinterface that is used for Internet access.
C. The CE router is configured as a BGP neighbor in both the global BGP process and inside the VPN in the VRF.
D. The PE-to-CE VPN and Internet routing are configured using two separate address-family ipv4 vrf commands, one for VPN routing and one for Internet routing.

 

Answer: A C

Question 2

When configuring Internet access using a separate MPLS VPN, which three statements are correct? (Choose three)

A. The Internet backbone is separate from the MPLS VPN backbone.
B. Two dedicated physical or logical links between the PE and the CE routers are required.
C. An Internet gateway is connected as a CE router to the MPLS VPN backbone.
D. An Internet gateway shall insert full Internet routing into the Internet VPN to achieve optimal routing.
E. The customer’s Internet access is enabled by combining the Internet VPN with the Customer VPN using overlapping VPN topology.

 

Answer: A C E

Question 3

BGP is used as the CE-PE routing protocol in an MPLS VPN. The customer routes are successfully propagated from the CE router to the ingress PE router, but they are not showing up on the egress PE router. What is the most likely cause of the problem?

A. There is a BGP-to-MPBGP redistribution error on the ingress PE router. 
B. There is a MPBGP-to-BGP redistribution error on the egress PE router.
C. One of the P routers is performing route summarization, breaking the path between the ingress and the egress PE routers into two LSPs. 
D. RTs attached to the CE routes exported by the ingress router are not matched by at least one of the import RTs on the egress PE router. 
E. A route reflector is used to propagate the routes from the ingress PE router to the egress PE router, thus breaking the LSP

 

Answer: D

Question 4

Refer to the exhibit and the following connectivity requirements. Which type of MPLS VPN is being implemented?

MPLS_VPN_type.jpg

Sites CE1A and CE1B require connectivity to each other.
Sites CE2A and CE2B require connectivity to each other.
Site CE1C requires connectivity to sites CE1A, CE1B, CE3A, and CE3B.
Site CE2C requires connectivity to sites CE2A, CE2B, CE3A, and CE3B.
Sites CE3A and CE3B require connectivity to each other and to CE1C and CE2C.

A. central services MPLS VPN
B. overlapping MPLS VPN
C. simple VPN
D. combinations of overlapping and central services MPLS VPN
E. combinations of simple and central services MPLS VPN

 

Answer: D

Question 5

Refer to the exhibit. Which two of these statements are correct? (Choose two)

BGP_Aggregate_address.jpg

A. Router C will aggregate the address and advertise only the summary address to its neighbors.
B. Router C will advertise the 160.0.0.0/8 prefix and all of the more specific prefixes.
C. Router C cannot aggregate the 160.0.0.0/8 prefix if it does not have a more specific prefix in its BGP table.
D. To aggregate the 160.0.0.0/8 prefix, router C must originate that prefix from within AS 300.
E. Router C will only aggregate the 160.0.0.0/8 prefix for any updates it is sending to AS 200.

 

Answer: B C

Categories: BGP + MPLS 642-691 Exam Tags:

MPLS over ATM

April 11th, 2011 5 comments

Here you will find answers MPLS over ATM Questions

Question 1

Refer to the exhibit. Which two of the following statements about the MPLS configurations are true? (Choose two)

MPLS_over_ATM.jpg

A. The VPI range being configured is the default VPI range.
B. The router is missing the mpls label protocol ldp configuration command on its ATM 0/0.1 subinterface to make it an LC-ATM enabled subinterface.
C. There is a problem with the configurations because the control VC should be set to 0 32 instead.
D. The ATM switch is using VC merge since VC merge is enabled by default.
E. For MPLS label allocations, both VPI 6 and 7 can be used.

 

Answer: D E

Explanation

We use the “mpls atm vpi <vci-range>” to configure the range of values to use in the virtual path identifier (VPI) field for label virtual circuits (LVCs).

The command “mpls atm control-vc <vpi> <vci>” is used to configure the control-VC virtual path identifier (VPI) and virtual circuit identifier (VCI) values for the initial link to the Multiprotocol Label Switching (MPLS) peer.

In the above exhibit, the command “mpls atm control-vc 6 32” means that we select 6 for VPI and 32 for VCI.

Note:

The default VPI range is 1-1.
The default VCI range is 33-65535.
When using the command mpls atm control-vc <vpi> <vci>, both end should have same configuration of this parameter.

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Fundamentals

April 10th, 2011 26 comments

Here you will find answers to BGP Fundamentals Questions

Question 1

Based on the topology diagram shown in the exhibit, when should BGP be used as the routing protocol between the customer and the ISP?

BGP.jpg

A. If physical link failures can not be detected by the link-level procedures.
B. If the customer wants to affect how the ISP will route the customer’s traffic out to the rest of the Internet.
C. If the ISP does not support static routing with the customer.
D. If the customer is using provider-assigned (PA) addresses inside the customer’s network.
E. If the customer is using private addresses inside the customer’s network.

 

Answer: A

Question 2

Based on the network diagram shown in the exhibit, what is the correct configuration on the customer edge router used to conditionally announce the customer networks to the ISP?

BGP_customer_edge_router.jpg

A. router bgp 65001
! neighbor commands not shown
network 192.168.8.0 mask 255.255.252.0
!
ip route 192.168.8.0 255.255.252.0 192.168.8.33

B. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0 summary-only
!
ip route 192.168.8.0 255.255.252.0 192.168.8.33

C. router bgp 65001
! neighbor commands not shown
network 192.168.8.0
network 192.168.9.0
network 192.168.10.0
network 192.168.11.0
!
ip route 192.168.8.0 255.255.255.0 null0
ip route 192.168.9.0 255.255.255.0 null0
ip route 192.168.10.0 255.255.255.0 null0
ip route 192.168.11.0 255.255.255.0 null0

D. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0 summary-only
!
router ospf 1
network 192.168.8.0 0.0.3.255 area 0

E. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0
!
ip route 192.168.8.0 255.255.252.0 null0

 

Answer: A

Question 3

Which two statements about a transit AS are correct? (Choose two)

A. A transit AS has eBGP connection(s) to only one external AS.
B. Routes between ASs are always exchanged via eBGP.
C. A transit AS uses an IGP like OSPF or ISIS to propagate the external networks within the transit AS.
D. Core routers within a transit AS normally use default routing to reach the external networks.
E. iBGP sessions can be established between non directly connected routers.

 

Answer: B E

Question 4

Which command is used to configure the external, confederation-wide AS number?

A. router(config)#router bgp {as-number}
B. router(config-router)#bgp confederation peers {as-number}
C. router(config-router)#bgp confederation identifier {as-number}
D. router(config-router)#bgp cluster-id {as-number}
E. router(config-router)#neighbor {ip address} remote-as {as-number}

Answer: C

Question 5

In a Transit AS, how do the internal routers within the Transit AS forward packets destined for the external networks using a scalable solution?

A. using the default route
B. using the IGP routes where the external networks are redistributed into the IGP by the edge routers 
C. using the EBGP routes where the external networks are redistributed into the IBGP by the edge routers 
D. using the IBGP routes, then using recursive lookup based on IGP information to resolve the BGP next-hop

 

Answer: D

Question 6

Given the following configurations, R2 and R3 are not able to successfully establish the iBGP session using the loopback 0 interfaces. What could be the cause of this problem?

iBGP_session.jpg

hostname R2
!
interface loopback 0
ip address 2.2.2.2
!
interface e0
ip address 10.1.1.1 255.255.255.0
no shut
!
interface e1
ip address 10.2.2.1 255.255.255.0
no shut
!
router bgp 65101
neighbor 172.16.1.1 remote-as 65100
neighbor 3.3.3.3 remote-as 65101
!
router eigrp 101
network 10.0.0.0
network 2.0.0.0
!
!
output omitted
!

hostname R3
!
interface loopback 0
ip address 3.3.3.3
!
interface e0
ip address 10.1.1.2 255.255.255.0
no shut
!
interface e1
ip address 10.2.2.2 255.255.255.0
no shut
!
router bgp 65101
neighbor 192.168.1.1 remote-as 65102
neighbor 2.2.2.2 remote-as 65101
!
router eigrp 101
network 10.0.0.0
network 3.0.0.0
!
A. The “No Sync” BGP configuration command is missing.
B. R2 and R3 are not using the loopback0 IP address as the source address for the BGP messages to each other.
C. The “network 2.0.0.0” BGP configuration command is missing on R2 and the “network 3.0.0.0” BGP configuration command is missing on R3.
D. The “neighbor 2.2.2.2 ibgp-multihop 2” BGP configuration command is missing on R3 and the “neighbor 3.3.3.3 ibgp-multihop 2” BGP configuration command is missing on R2.

 

Answer: B

Question 7

What are two purposes of the BGP scan-time command? (Choose two)

A. to tune the BGP process which walks the BGP table and confirms the reachability of next hops
B. to allow faster detection of downed BGP peers
C. to improve BGP convergence time
D. to tune the BGP update interval
E. to decrease the effects of unstable routes by increasing the route suppression time

 

Answer: A C

Question 8

If there is no exact match in the local routing table, what three conditions would result in BGP introducing the classful network 172.0.0.0 with the mask 255.0.0.0 into the BGP table? (Choose three)

A. no auto-summary is configured under the router bgp {as no.} command
B. network 172.0.0.0 is configured under the router bgp {as no.} command
C. any classful network must exist in the BGP table
D. auto-summary is enabled under the router bgp {as no.} command
E. the routing table contains the subnet 172.172.172.0 with a subnet mask of 255.255.255.0
F. a classless network must exist in the BGP table

 

Answer: B D E

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Fundamentals 2

April 9th, 2011 24 comments

Here you will find answers to BGP Fundamentals – Part 2

Question 1

In a multihomed environment with two ISP connections, which two statements are true? (Choose two)

A. The customer should not be configured to act as a transit AS between the two ISPs.
B. It is recommended that the multi-homed customer use a registered (public) AS number.
C. AS-Path prepending can be configured on the customer’s edge router to influence the BGP path selection process for the outbound traffic (traffic from the customer to the ISPs).
D. The customer can use Local Preference on the customer’s edge routers to influence the BGP path selection process for the inbound traffic (traffic from the ISPs to the customer).
E. The advertisement of the customer’s IP address space can be conditioned by the customer’s edge routers by using a static route to the nullO interface and by using the proper network statement under router bgp

 

Answer: A B

Question 2

Which four attributes are used by BGP to detect routing loops? (Choose four)

A. AS-Path
B. Cluster ID
C. Cluster List
D. Originator ID
E. Community ID

 

Answer: A B C D

Question 3

Which three statements are true about route reflectors? (Choose three)

A. If the route is learned from an EBGP peer by the route reflector, it is reflected to all IBGP and EBGP peers.
B. If the route is learned from a non-client IBGP peer by the route reflector, it is reflected to all EBGP peers only.
C. If the route is learned from a non-client IBGP peer by the route reflector, it is reflected to EBGP peers and clients only.
D. If the route is learned from a client IBGP peer by the route reflector, it is reflected to all clients only, except the originating client.
E. If the route is learned from a client IBGP peer by the route reflector, it is reflected to all EBGP peers, non-clients, and clients (except the originating client).

 

Answer: A C E

Question 4

Based on the following show ip bgp neighbors 2.2.2.2 output, which two statements are true? (Choose two)

R1#show ip bgp neighbors 2.2.2.2
BGP neighbor is 2.2.2.2, remote AS 102, internal link
Index 1, Offset 0, Mask 0x2
BGP version 4, remote router ID 66.0.0.1
BGP state=Established, table version=1, up for 00:14:52
Last read 00:00:52, hold time is 180, keepalive interval is 60 seconds
Minimum time between advertisement runs is 5 seconds
Received 233 messages, 0 notifications, 0 in queue
Sent 206 messages, 0 notifications, 0 in queue
Prefix advertised 0, suppressed 0, withdrawn 0
Connections established 17; dropped 16
Last reset 00:15:02, due to User reset
18 accepted prefixes consume 576 bytes, maximum limit 20
Threshold for warning message 80%
0 history paths consume 0 bytes

A. R1 has accepted 20 prefixes from the 2.2.2.2 IBGP neighbor.
B. R1 generated a warning message to the router’s console after the 2.2.2.2 IBGP neighbor sent 16 prefixes to R1.
C. R1 generated a warning message to the router’s console after the 2.2.2.2 IBGP neighbor sent 15 prefixes to R1.
D. R1 will drop its neighbor relationship to the 2.2.2.2 IBGP neighbor if 2.2.2.2 sends two more additional prefixes to R1.
E. R1 will drop its neighbor relationship to the 2.2.2.2 IBGP neighbor if 2.2.2.2 sends three more additional prefixes to R1.

 

Answer: B E

Question 5

During the autonomous system number migration process, which BGP feature allows a BGP router to act as a router within one autonomous system to some BGP neighbors but also appear to be in another autonomous system to other neighbors?

A. remove-private-as
B. local-as
C. as-path prepending
D. AS override
E. Site-of-Origin (Soo)

 

Answer: B

Question 6

Based on this configuration, which two peering router neighbor statements are correct? (Choose two)

router bgp 50001
neighbor 192.168.1.1 remote-as 50001
neighbor 10.1.1.1 remote-as 50002
neighbor 10.1.1.1 local-as 50003
!
output omitted

A. EBGP – neighbor 10.1.1.2 remote-as 50003
B. EBGP – neighbor 10.1.1.2 remote-as 50001
C. EBGP – neighbor 10.1.1.2 remote-as 50001 and neighbor 10.1.1.2 local-as 50003
D. IBGP – neighbor 192.168.1.2 remote-as 50001
E. IBGP – neighbor 192.168.1.2 remote-as 50003
F. IBGP – neighbor 192.168.1.2 remote-as 50003 and neighbor 192.168.1.2 local-as 50001

 

Answer: A D

Question 7

Which command is used to advertise a summary route while suppressing only a subset of the more specific routes?

A. network {ip prefix} {mask}
B. network {ip prefix} {mask} unsuppress-map {route-map-name}
C. aggregate-address {ip prefix} {mask}
D. aggregate-address {ip prefix} {mask} summary-only
E. aggregate-address {ip prefix} {mask} suppress-map {route-map-name}
F. aggregate-address {ip prefix} {mask} as-set summary-only

 

Answer: E

Question 8

What is the correct command to set the BGP scanner interval to two minutes?

A. bgp scan-time 2
B. bgp scan-time 120
C. bgp scan-time 2 60
D. The maximum scanning interval cannot exceed one minute

 

Answer: D

Question 9

Given the AS-path of (51002 51003) 51001 i from the show ip bgp output, what is the origin?

A. AS 51001
B. AS 51002
C. AS 51003
D. (51002 51003)
E. IGP
F. IBGP

 

Answer: E

Question 10

AS-PATH prepending is used in AS1 in order to influence the return traffic path from AS 5 to AS 1 through the higher speed path via AS 2. ______ needs to be configured for AS-Path prepending and a minimum of ______ of the AS number should be prepended.

AS_PATH.jpg

A. R1; one copy
B. R2; one copy
C. R1; two copies
D. R2; two copied
E. R2; three copies

Answer: C

Question 11

Which two configuration commands will complete the BGP configuration on R1 so it will conditionally announce the 172.0.0.0/8 prefix to R4 via BGP? (Choose two)

BGP_prefix.jpg

hostname R1
!
output omitted
!
1. ______________________
!
router bgp 65001
neighbor 172.16.1.1 remote-as 65001
neighbor 2.2.2.2 remote-as 65001
neighbor 4.4.4.4 remote-as 387
!
2. ______________________

A. 2. network 172.16.0.0
auto-summary
B. 2. network 172.0.0.0 mask 255.0.0.0
C. 1. ip route 172.0.0.0 255.0.0.0 null0
D. 1. ip route 172.0.0.0 255.0.0.0 null0 255
E. 1. ip route 172.0.0.0 255.0.0.0 172.16.1.1
F. 2. aggregate-address 172.0.0.0 mask 255.0.0.0

 

Answer: B E

Question 12

R2 is configured to prepend AS number 65102 in updates to R3. Which statement is true?

BGP_AS_Prepend.jpg

A. The BGP updates from R2 to R3 will be rejected by R3 due to loop prevention.
B. The EBGP session between R2 and R3 will be dropped due to an AS-Path prepend configuration error.
C. The AS-Path length via AS 65102 will increase to influence the return traffic path selected by the remote ASs.
D. The AS-Path length via AS 65102 will decrease to influence the return traffic path selected by the remote ASs.
E. The AS-Path prepend configuration command using the remote AS number (65102) will be rejected by IOS at R2.

 

Answer: A

Question 13

Refer to the partial topology diagram shown.

BGP_source_update.jpg

Service Provider 1 (SP1) assigned the customer an AS number of 65275.
Service Provider 2 (SP2) assigned an AS number of 65745 to the customer.
The customer decides to use AS 65275 internally.
Which of the following is the correct partial router configuration to cause updates from CR1 to SP1 to report a source AS of 65275, while updates from CR2 to SP2 report the source AS of 65745 in addition to AS 65275?

A.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65275
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65745
neighbor 10.1.1.1 remote-as 65275

B.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65745
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65745
neighbor 10.1.1.1 remote-as 65275

C.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 1.1.1.1 local-as 65745
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65275
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65745
neighbor 10.1.1.1 remote-as 65275

D.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65745
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65275
neighbor 10.1.1.1 remote-as 65275

 

Answer: A

Question 14

In the diagram, the customer is using static routing to connect to the ISP. Which configuration on the ISP edge routers will enable load balancing and backup of the traffic to the customer?

BGP_ISP_edge_router.jpg

A.
R1
ip route 10.1.1.0 255.255.255.128 serial 0
R2
ip route 10.1.1.128 255.255.255.128 serial 0

B.
R1
ip route 10.1.1.0 255.255.255.0 serial 0
R2
ip route 10.1.1.128 255.255.255.0 serial0

C.
R1
ip route 10.1.1.0 255.255.255.128 serial 0
ip route 10.1.1.128 255.255.255.128 serial 0
R2
ip route 10.1.1.128 255.255.255.128 serial 0
ip route 10.1.1.0 255.255.255.128 serial 0

D.
R1
ip route 10.1.1.0 255.255.255.128 serial 0
ip route 10.1.1.0 255.255.255.0 serial 0
R2
ip route 10.1.1.128 255.255.255.128 serial 0
ip route 10.1.1.0 255.255.255.0 serial 0

 

Answer: D

Question 15

An OSPF LSA type 1 route is redistributed into MP-BGP. That same route is then redistributed back from MP-BGP into OSPF on another PE router. In this case, which LSA type on the destination CE router will the OSPF route appear as?

A. LSA type 1
B. LSA type 2
C. LSA type 3
D. LSA type 4
E. LSA type 5
F. LSA type 7

 

Answer: C

Question 16

When using the redistribute ospf {process-id} command, which types of OSPF routes will be redistributed into BGP?

A. all internal (interarea and intra-area) OSPF routes
B. all external OSPF routes
C. all external OSPF routes except type 7 LSAs
D. both internal and external OSPF routes
E. only classful OSPF routes without the subnet option
F. only external OSPF routes without the match option

 

Answer: A

Question 17

What best describes the following configuration example of allowas-in?

router bgp 100
address-family ipv4 vrf CustomerA
neighbor 195.12.4.5 remote-as 123
neighbor 195.12.4.5 activate
neighbor 195.12.4.5 allowas-in 2

A. permits incoming BGP updates defined by access-list 2
B. permits incoming BGP updates defined by class-map 2
C. permit incoming BGP updates defined by route-map 2
D. permits incoming BGP updates with no more than two occurrences of AS 100 in the AS path
E. permits incoming BGP updates with no more than two occurrences of AS 123 in the AS path

 

Answer: D

Question 18

Who should use private AS numbers?

A. multihomed customers who configured their AS as a transit AS
B. customers multihomed to two different ISPs
C. customers multihomed to a single ISP using multiple permanent links
D. customers connected to a single ISP using a single permanent link

 

Answer: C

Question 19

Refer to the outputs shown in the exhibit. What could be preventing the R1 router from receiving any prefixes from the R2 BGP neighbor?

R1#show ip bgp summary
BSP router identifier 199.199.199.199, local AS number 20
BGP table version is 45, main routing table version 45
44 network entries using 4444 bytes of memory
81 path entries using 3888 bytes of memory
13 BGP path attribute entries using 780 bytes of memory
11 BGP AS-PATH entries using 264 bytes of memory
4 BGP route-map cache entries using 64 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 9440 total bytes of memory
BGP activity 88/44 prefixes, 191/110 paths, scan interval 5 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.1.17 4 1 1628 2693 45 0 0 00:42:22 31
192.168.20.22 4 22 70 73 45 0 0 00:42:26 31
192.168.31.1 4 65002 172 274 0 0 0 00:00:13 Idle

R1#telnet 192.168.31.1
Trying 192.168.31.1 … Open

User Access Verification

Password: cisco

R2#sh run | begin bgp
router bgp 65002
bgp confederation identifier 1
bgp confederation peers 65001
network 10.0.0.0
neighbor 192.168.31.2 remote-as 20

A. There is a TCP session establishment problem between R1 and R2.
B. The no sync command is missing on R2.
C. The no sync command is missing on R1.
D. R2 is using the wrong AS number in its neighbor 192.168.31.2 remote-as statement.
E. R1 is using the wrong AS number in its neighbor 192.168.31.1 remote-as statement.
F. Both R1 and R2 are not using a loopback address to source their BGP packets.

 

Answer: E

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Fundamentals 3

April 8th, 2011 9 comments

Here you will find answers to BGP Fundamentals – Part 3

Question 1

Refer to the configuration shown. What could cause the BGP prefixes from the 10.1.1.1 BGP peer to be absent from the routing table?
!
interface loopback0
ip address 10.10.10.10 255.255.255.255
!
router bgp 51001
synchronization
bgp log-neighbor-changes
bgp confederation identifier 51000
bgp confederation peers 51002 51003
network 10.0.0.0
neighbor 192.168.1.14 remote-as 51021
neighbor 192.168.1.18 remote-as 51022
neighbor 10.1.1.1 remote-as 51001
neighbor 10.1.1.1 next-hop-self
neighbor 10.1.1.1 update-source Loopback0
neighbor 10.2.2.1 remote-as 51002
neighbor 10.2.2.1 ebgp-multihop 255
neighbor 10.2.2.1 update-source Loopback0
neighbor 10.3.3.1 remote-as 51003
neighbor 10.3.3.1 ebgp-multihop 255
neighbor 10.3.3.1 update-source Loopback0
auto-summary
!
router rip
network 10.0.0.0
!

A. intraconfederation EBGP configurations error
B. autosummarization
C. ebgp-multihop issue
D. BGP synchronization
E. EBGP configurations error

 

Answer: D

Question 2

The core routers within a transit AS are running both IBGP and IGP. The edge routers within the transit AS are using the next-hop-self option to establish the IBGP sessions. What can be implemented to improve the routing performance to all external prefixes?

A. enable route redistribution from BGP into IGP
B. disable BGP synchronization on all the core routers
C. enable CEF on all the core and edge routers
D. enable route redistribution from IGP into BGP
E. use route reflectors within the core

 

Answer: C

Question 3

What does the BGP synchronization rule prevent?

A. sub-optimal routing within a transit AS
B. routing black holes within a transit AS
C. routing loops within a transit AS
D. recursive routing lookups
E. scalability issues of redistributing BGP into an IGP

 

Answer: B

Question 4

Which one of these statements regarding intraconfederation EBGP sessions is correct?

A. Intraconfederation EBGP neighbors must be directly connected.
B. An intraconfederation EBGP session behaves like an IBGP session when propagating routing updates. 
C. Member-AS numbers are removed when a router sends a BGP update over an intraconfederation EBGP session. 
D. Updates from an intraconfederation EBGP neighbor are subject to the BGP split horizon rule. 
E. Intraconfederation EBGP sessions must be established over loopback interfaces.

 

Answer: B

Question 5

What state will a BGP session move to immediately after the router sends a BGP Open message to its neighbor?

A. active
B. OpenConfirm
C. OpenSent
D. established
E. idle

 

Answer: C

Question 6

In the diagram, the customer is using BGP to connect to a single ISP ober two permanent links. In this scenario, which input and output prefix-list filtering is typically enabled on the ISP routers? (Choose two)

connect_ISP_multiple_links.jpgA.    ip prefix-list test-in permit 10.1.1.0/24 le 32
B.    ip prefix-list test-in permit 10.0.0.0/8 le 32
C.    ip prefix-list test-in permit 0.0.0.0/0
D.    ip prefix-list test-out permit 10.1.1.0/24 le 32
E.    ip prefix-list test-out permit 10.0.0.0/8 le 32
F.    ip prefix-list test-out permit 0.0.0.0/0

 

Answer: A F

Question 7

Refer to the BGP configurations and the show outputs in the diagram. What are two reasons why the 197.1.0.0/16 and 192.168.1.0/30 prefixes are not in the BGP table of WGR1? (Choose two)

router bgp 1
no synchronization
bgp log-neighbor-changes
network 192.168.1.0
network 197.1.0.0 mask 255.255.0.0
neighbor 192.168.1.14 remote-as 22
auto-summary

BGP_show_ip_route.jpg

BGP_show_ip_bgp.jpg

A. auto-summary is enabled.
B. The 197.1.0.0/16 prefix is not in the routing table of WGR1.
C. The 192.168.1.0/30 prefix is not in the routing table of WGR1.
D. The network 192.168.1.0 command defaults to the classful mask.
E. The aggregate-address 197.1.0.0 255.255.0.0 summary-only command should be used instead of the network 197.1.0.0 mask 255.255.0.0 command.

 

Answer: B D

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Prefix-Filter

April 7th, 2011 5 comments

Here you will find answers to BGP Prefix-Filter Questions

Question 1

What does the following command accomplish?

sanjose#clear ip bgp 10.1.1.1 in prefix-filter

A. The sanjose router will perform an outbound soft reconfig to the 10.1.1.1 neighbor.
B. The sanjose router will send out the ORF prefix-list so that a new route refresh will be received from the 1.1.1 neighbor. C. The 10.1.1.1 router will perform an inbound soft reconfig on the updates from the sanjose neighbor.
D. The 10.1.1.1 router will send out the ORF prefix-list so that a new route refresh will be received from the sanjose neighbor.
E. The bgp session between the sanjose and the 10.1.1.1 router will be reset so that all the new bgp updates from the 10.1.1.1 router can be processed by the inbound prefix-list at the sanjose router. 
F. The bgp session between the sanjose and the 10.1.1.1 router will be reset so that all the new bgp updates from the sanjose router can be processed by the inbound prefix-list at the 10.1.1.1 router.

 

Answer: B

Question 2

The MPLS VPN provider is using a separate Internet VPN to provide Internet access to its MPLS VPN customers. Currently, all of its customers are not able to access the Internet. The partial provider’s CE-lnternet router configuration is shown below. Based on the configuration, what could be the cause of the problem?

ip route 0.0.0.0 0.0.0.0 10.1.1.1
!
router bgp 51001
network 0.0.0.0
neighbor 10.2.2.2 remote-as 51002 ! PE neighbor router
neighbor 10.2.2.2 prefix-list test1 out
neighbor 10.3.3.3 remote-as 51001 ! Another Internet router
neighbor 10.3.3.3 prefix-list test2 out
!
ip prefix-list test2 permit 0.0.0.0/0
ip prefix-list test1 permit 0.0.0.0/0 ge 1

A. The test2 prefix-list should be applied to the 10.2.2.2 neighbor and the test1 prefix-list should be applied to the 10.3.3.3 neighbor. 
B. Both prefix-lists should be applied in the “in” direction instead of the “out” direction. 
C. The network command is missing the mask 0.0.0.0 option.
D. The network command is missing the mask 255.255.255.255 option. 
E. The neighbor 10.2.2.2 activate and the neighbor 10.3.3.3 activate commands are missing.

 

Answer: A

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Redistribute

April 6th, 2011 3 comments

Here you will find answers to BGP Redistribute

Question 1

When routes between MP-BGP and RIP are being redistributed, what does the option metric transparent do?

A. copies the BGP MED into the RIP hop count
B. copies the BGP local preference into the RIP hop count
C. copies the RIP hop count into the BGP local preference
D. copies the RIP hop count into the BGP MED
E. uses the default seed metric when redistributing from MP-BGP into RIP
F. uses the default seed metric when redistributing from RIP into MP-BGP

 

Answer: A

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Route Dampening

April 5th, 2011 6 comments

Here you will find answers to BGP Route Dampening Questions

Question 1

As the penalty for a flapping route decreases and falls below a certain limit, the route is unsuppressed. What is the name of that limit?

A. half-life limit
B. suppress limit
C. max-suppress-time limit
D. reuse limit
E. unsuppress limit
F. penalty limit

 

Answer: D

Question 2

Which configuration will enable the R1 router in the AS51003 sub-AS (member-AS) as a route reflector with neighbors 10.1.1.1 and 10.2.2.2 as its route-reflector clients?

A.
!
R1
router bgp 51003
bgp confederation identifier 55111
bgp confederation peers 51001 51002
neighbor 10.1.1.1 remote-as 51003
neighbor 10.2.2.2 remote-as 51003
neighbor 10.1.1.1 route-reflector-client
neighbor 10.2.2.2 route-reflector-client

B.
!
R1
router bgp 51003
bgp confederation identifier 55111
bgp confederation peers 51001 51002
neighbor 10.1.1.1 remote-as 51001
neighbor 1Q.2.2.2 remote-as 51002
neighbor 10.1.1.1 route-reflector-client
neighbor 10.2.2.2 route-reflector-client

C.
!
R1
router bgp 55111
bgp confederation identifier 51003
neighbor 10.1.1.1 remote-as 51003
neighbor 10.2.2.2 remote-as 51003
neighbor 10.1.1.1 route-reflector-client
neighbor 10.2.2.2 route-reflector-client

D.
!
R1
router bgp 55111
bgp confederation identifier 51003
neighbor 10.1.1.1 remote-as 55111
neighbor 10.2.2.2 remote-as 55111
neighbor 10.1.1.1 route-reflector-client
neighbor 10.2.2.2 route-reflector-client

 

Answer: A

Categories: BGP + MPLS 642-691 Exam Tags:

BGP Route Reflectors

April 4th, 2011 15 comments

Here you will find answers to BGP Route Reflectors Questions

Question 1

Which configuration task requires configuring the bgp cluster-id {cluster-id} command?

A. configuring the member ASs within a BGP confederation
B. configuring the BGP confederation ID
C. configuring hierarchical BGP confederations
D. configuring redundant BGP confederations
E. configuring hierarchical route reflectors
F. configuring redundant route reflectors

 

Answer: F

Question 2

Based on the R1 router BGP configuration shown, which three statements are correct? (Choose three)

hostname R1 ;
router bgp 50001
bgp confederation identifier 50101
bgp confederation peers 50002 50003
neighbor 10.1.1.1 remote-as 50001
neighbor 10.2.2.2 remote-as 50001
neighbor 10.3.3.3 remote-as 50001
neighbor 10.1.1.1 router reflector-client
neighbor 10.2.2.2 router reflector-client
neighbor 10.3.3.3 route-reflector-client
neighbor 10.4.4.4 remote-as 50002
neighbor 10.5.5.5 remote-as 50003
neighbor 192.168.100.1 remote-as 50102
neighbor 192.168.100.1 route-map setlp in
neighbor 192.168.100.1 route-map setmed out
no sync
!

A. R1 is in AS 50101 according to the 192.168.100.1 neighbor.
B. R1 is in AS 50101 according to the 10.1.1.1 neighbor.
C. The 192.168.100.1 neighbor must be directly connected to R1.
D. R1 is a route-reflector client.
E. The 10.4.4.4 neighbor is an EBGP neighbor.
F. BGP updates coming in from the 192.168.100.1 neighbor must be processed by the setlp route-map.

 

Answer: A C F

Question 3

Refer to the diagram. What should be changed within AS 50001 to improve the route reflector design?

improve_route_design.jpg

A. Add a physical link between R1 and R2.
B. Add a physical link between the clients (R3 and R4, and between R4 and R5).
C. Remove the iBGP session between the two redundant RRs (R1 and R2).
D. Add an iBGP session between each pair of clients (between R3 and R4, R4 and R5).
E. Make R4 the RR and R1 and R2 its clients. R3 and R5 should be a non-RR/non-client.

 

Answer: A

Question 4

Based on the network diagram shown in the exhibit, both R5 and R6 are clients of the R2 RR. When the 10.0.0.0/8 iBGP update from R3 is received by the R2 RR, which router(s) will R2 reflect the update to?

iBGP_Update.jpg

A. R1 only
B. R5 and R6
C. R5, R6 and R1
D. R4, R5 and R6
E. R4, R5, R6 and R1
F. to no other router

 

Answer: C

Question 5

Which show command can be used to display the originator ID and cluster-list?

A. show ip bgp
B. show ip bgp sum
C. show ip route bgp
D. show ip route {prefix}
E. show ip bgp {prefix}
F.show ip bgp neighbors {ip address}

 

Answer: E

Categories: BGP + MPLS 642-691 Exam Tags:

Simple MPLS GNS3 Lab

April 4th, 2011 6 comments

In this article we will do a very basic lab to understand the fundamental concept of MPLS.

IOS: c3660-jk9o3s-mz.124-17.bin

Topology:

Basic_MPLS_GNS3_Topology.jpg

First configure EIGRP AS 100 on R1, R2 and R3

R1:

R1#configure terminal
R1(config)#interface f0/1
R1(config-if)#ip address 192.168.12.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#router eigrp 100
R1(config-router)#network 192.168.12.0 0.0.0.255

R2:

R2#configure terminal
R2(config)#interface f0/0
R2(config-if)#ip address 192.168.12.2 255.255.255.0
R2(config-if)#no shutdown
R2(config)#interface f0/1
R2(config-if)#ip address 192.168.23.2 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit
R2(config)#router eigrp 100
R2(config-router)#network 192.168.12.0 0.0.0.255
R2(config-router)#network 192.168.23.0 0.0.0.255

R3:

R3#configure terminal
R3(config)#interface f0/0
R3(config-if)#ip address 192.168.23.3 255.255.255.0
R3(config-if)#no shutdown
R3(config-if)#exit
R3(config)#router eigrp 100
R3(config-router)#network 192.168.23.0 0.0.0.255

Now check these 3 routers with the show ip route command, we can see all the routers learned all the routes in EIGRP AS 100.

Read more…

Categories: Practice CCIP GNS3 Lab Tags:

MPLS TDP Neighbor Lab Sim

April 2nd, 2011 52 comments

Question

R1 and R2 are not able to establish MPLS TDP neighbor relationship between them. Use various show commands to troubleshoot the problem then use the proper configuration command(s) to solve the MPLS TDP issue. Once R1 and R2 can see each other as MPLS TDP neighbor, then you have successfully completed the simulation.

Privileged mode password: mpls

MPLS_TDP.jpg

 

Answer and Explanation

Read more…

Categories: Lab Sim Tags:

BGP Prefix-Based Filtering Lab Sim

April 1st, 2011 52 comments

Question

After the network administrator modified the configuration on the WGR1 router, the WGR1 router is not able to receive any prefixes from AS22. The network administrator original intent was to only filter out a particular prefix from AS22.

Fix the configuration on the WGR1 router to solve the problem. You have correctly solved the problem once the WGR1 router is able to receive 23 prefixes from AS22.

Enable secret password is cisco

Prefix_Based_BGP.jpg

 

Answer and Explanation

Read more…

Categories: Lab Sim Tags:

Drag and Drop Questions

March 31st, 2011 9 comments

Here you will find answers to Drag and Drop Questions

Question 1

Drag and drop the proper command in the proper order to create a MP-BGP session between two PE routers that will be used to support the RED VPN

BGP_neighbor.jpg

 

Answer:

Command 1: router bgp 65001
Command 2: neighbor 172.16.1.2 remote-as 65001
Command 3: neighbor 172.16.1.2 update-source loopback 0
Command 4: address-family vpnv4
Command 5: neighbor 172.16.1.2 activate

Question 2

Drag and drop the proper command in the proper order to configure EBGP as the CE to PE routing protocol for VPN RED on a PE router.

EBGP.jpg

 

Answer:

Command 1: router bgp 65001
Command 2: address-family ipv4 vrf RED
Command 3: neighbor 172.16.1.2 remote-as 65002

Question 3

Drag and drop the proper command in the proper order to redistribute the RED VPN routes from the EIGRP vrf into the BGP vrf

EIGRPvrf_BGPvrf.jpg

 

Answer:

Command 1: router bgp 65001
Command 2: address-family ipv4 vrf RED
Command 3: redistribute eigrp 101

Question 4

Drag the BGP MED function on the left to the command that enables it on the right. Not all apply

BGP_MED.jpg

 

Answer:

bgp deterministic med: Enforce the comparison of MED between all paths received from the same autonomous system
bgp always-compare-med: Allow the comparison of MED for paths from neighbors in different autonomous systems
bgp bestpath med-confed: Enable MED comparison among paths learned from confederation peers

Question 5

CE1A and CE2A belong to the Customer_A VPN. Select the correct command for the PE1 router to establish static routing from PE1 to the CE1A 192.168.1.0/24 network by selecting them from the dropdown menus below. Some of the commands must be entered in the correct order. Also enable propagation of the static route into MP-iBGP. Assume the MP-iBGP session between PE1 and PE2 have been configured already.

BGP_commands.jpg

 

Answer:

1. ip route vrf Customer_A 192.168.1.0 255.255.255.0 10.1.1.2 Serial0/0
2. router BGP 50111
3. address-family ipv4 vrf Customer_A
4. redistribute static

Categories: BGP + MPLS 642-691 Exam Tags:

Share your MPLS + BGP Experience

March 30th, 2011 851 comments

Please share with us your experience after taking the MPLS + BGP 642-691 exam, your materials, the way you learned, your recommendations…

Your posts are warmly welcome!

Please don’t ask for links to download copyright materials here…

Categories: BGP + MPLS 642-691 Exam Tags: