Sunday, January 30, 2011

CCNP Questions And Answers For Who Preparing For Exams

CCNP Questions and Answers

A postal address has three components that can be used to deliver mail: state, city, and street. A phone number has an area code and exchange. At the core layer, mail can be delivered to the next post office based on only the state or city and state information. A phone number is delivered at the core layer based on the area code.

A default route is used if there is not a specific entry in the routing table for the destination.

Routing moves a letter or telephone call to the access layer (as in a street or telephone exchange). Switching makes the final delivery. A switching decision is made on the part of the address that is not used in routing (as in the street number or last four digits of a phone number).

At the core layer in the postal system, the only information that is needed to make a routing decision is the state or city/state information. The specific street names and street numbers are hidden, the core layer does not need this information. At the core layer in the telephone system, the area code is used to make a routing decision. The specific exchange or last four digits of the phone number are not needed, or hidden, from the core layer.

If a delivery system is not divided into access, distribution, and core layers, every point in the system needs to maintain every possible destination address to make a delivery decision. The use of a layered system means each layer needs only the information necessary to deliver to the next layer, either above or below.

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Using multiple protocols is modular and allows changes to one protocol without affecting the others. For example, if the addressing protocol is dependent on the delivery protocol, changes to one would imply changes need to be made to the other.

The airport system. At the core routing level, there are major hub airports such as Denver, Chicago, New York, and Atlanta. The core airports are responsible for routing people and cargo to major geographical areas. Core airports connect with regional airports that serve a specific area; regional airports are at the distribution layer. Finally, to reach your final destination, you can take a bus, a cab, a train, or rent a car. This can be considered the access layer.

The source address is not used unless the letter needs to be returned to the sender. Using the destination address, the access level post office in New York examines the state, city, and street information to determine if it is directly connected to the destination. If not, the letter is sent to the distribution layer post office using a default route. The distribution layer post office also examines the state, city, and street information to determine if it is directly connected to an access layer post office servicing the particular street. If it isn't, the letter is routed to the core level using a default route. The core level post office examines the state name, and if the state name does not equal New York, the letter is delivered to the core post office for the state of California. The California core post office delivers the letter to the distribution post office that handles the city of San Diego. The San Diego distribution post office delivers the letter to the access post office that handles the destination street. Finally, the access level switch delivers the letter to the proper destination.

The street name and number are the access layer components. The city name is the distribution layer component. The state name is the core layer component.
The last four digits are the used at the access layer to identify a particular telephone. The next three numbers are used at the distribution layer to identify an exchange that services several phone numbers. The area code is used at the core level for routing between different regions.

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224, 252, 128, 240, and 63 (64 – 1)
Answer: FA 16 = 250 10, CE16 = 20610, 1216 = 18 10, and 34 16 = 52 10

FACE1234 16 = 250.206.18.52 dotted decimal

A2F59D8B

Convert to dotted hexadecimal first, and then convert each hexadecimal number pair to decimal.

A2.F5.9D.8B then 162.245.157.139
24275316613 8

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Answer is True

Convert each octal digit into three binary digits, and then convert the binary result to hexadecimal.

001 010 011 100 101 110 111 000

0010 1001 1100 1011 1011 1000

29CBB8

111 011 100 010 001 101

0111 0011 0100 0010 0001 0101 2

142.16.73.255

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198.4.81.0/27 and the subnets are:

198.4.81.0/27

198.4.81.32/27

198.4.81.64/27

198.4.81.96/27

198.4.81.128/27

198.4.81.160/27

198.4.81.192/27

198.4.81.224/27

198.4.81.127

162.8.0.0/22

162.8.4.0/22

162.8.8.0/22

162.8.12.0/22

132.16.0.0/11 because it matches more network bits than 132.0.0.0/8. Network 132.16.233.0/22 and 132.19.237.5/22 do not match on the network address.

172.16.53.97 through 172.16.53.126

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26 :: How many two-host subnets can be made from a /24 network?

64 because 2 bits are needed for the hosts on the network, leaving 6 bits for the subnet.

27 :: What is the full IPv6 address represented by FF02::130F:5?

FF02:0000:0000:0000:0000:0000:130F:0005

28 :: Explain the difference between a classful and a classless routing protocol.

Classless routing protocols advertise subnet mask information along with the network prefixes. Classful routing protocols do not. Therefore, for a classful protocol, all subnets for the major network number being used must be the same length. Also, classful protocol cannot support discontiguous networks prefixes.

29 :: What are the states that an EIGRP route can be in and what do these states mean?

The passive state means that a router has a successor for a route. The active state means that a router does not have a successor or feasible successor for a route and is actively sending queries to neighbors to get information about the route.

30 :: Explain the relationship between reported distance and feasible distance and how they determine successors and feasible successors.

The reported distance to a route that is sent to another router is the feasible distance on the reporting router. Feasible distance is the reported distance plus the metric between the receiving and reporting routers. The route with the lowest feasible distance is the successor. Any routes with a reported distance that is less than the feasible distance are feasible successors.

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You need to examine the third byte because that is the byte where the four prefixes differ:

0 = 0 0 0 0 0 0 0 0

32 = 0 0 1 0 0 0 0 0

64 = 0 1 0 0 0 0 0 0

96 = 0 1 1 0 0 0 0 0

The last 7 bits are irrelevant, so the mask is 1 0 0 0 0 0 0 0 and the EIGRP command is ip summary-address eigrp 1 10.1.0.0 255.255.128.0.
Areas allow the design of a hierarchical network. Routes can be summarized or blocked in an area to reduce the amount of routing information on internal OSPF routers.

OSPF databases on routers in the same area must be identical. If route summarization was allowed within an area, some routers would have specific routes and some routers would have summary routes for routes in the area. If this were allowed, the databases for the area would never agree.
OSPF intra-area and interarea routes, and a default route. External routes are not advertised into a stub area.

OSPF intra-area routes and a default route. OSPF interarea and external routes are not advertised into a totally stubby area.

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OSPF intra-area and interarea routes, and possibly a default route. External routes from ABRs are blocked, and external routes from ASBRs are converted to N1 or N2 routes.
OSPF intra-area routes and a default route. External routes from ABRs are blocked, and external routes from ASBRs are converted to N1 or N2 routes.
An E1 route contains the OSPF cost to reach the ASBR plus the cost from the ASBR to the external route. An E2 route contains only the cost from the ASBR to the external route.

ABR, internal router, and ASBR.

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OSPF routes are summarized on an ABR. External routes are summarized on an ASBR.

If physical interfaces are only used, the OSPF router ID is the highest IP address assigned to an active physical interface. If loopback interfaces are used, the OSPF router ID is the highest IP address assigned to a loopback interface. If the router-id command is used with the OSPF configuration, the address used with this command will be the router ID.

The router with the highest interface priority will be the router ID. If all the interface priorities on the multi-access network are the same, the router with the highest router ID will be the DR.

First, calculate the shortest path to an ABR.

Second, calculate the shortest path across area 0 to an ABR that is attached to the destination area.

Third, calculate the shortest path across the destination area from the ABR to the destination network.

To connect a nonzero area to the backbone if the nonzero area becomes disconnected from the backbone. A virtual link can also be used if the backbone, or area 0, becomes discontiguous.

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By default, the cost of an OSPF interface is 100,000,000/(Interface Bandwidth). The constant 100,000,000 can be changed using the auto-cost reference-bandwidth command.

Area 1 range 188.14.19.0 255.255.255.192

The number of OSPF databases on a router is equal to the number of OSPF areas configured on the router.

110

EIGRP has an administrative distance of 90.

IGRP has an administrative distance of 100.

OSPF has an administrative distance of 110.

RIP has an administrative distance of 120.

Therefore, the EIGRP route is preferred.

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An NSAP address has a length of 8 to 20 bytes and consists of three components:

► One to 13 byte area ID

► Six byte system ID

► One byte NSAP selector that is always equal to zero for a router
The loopback address written in dotted decimal and using three digits for each byte has a value of 135.077.009.254. The system ID is 13.50.77.00.92.54.

OSPF has a backbone area or area 0. All nonzero areas must be connected to the backbone through a router or a virtual link. IS-IS has a backbone area made up of a contiguous chain of Level 2 capable routers.

Level 1 routing is routing between destinations in the same IS-IS area

Intra-area routing.

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A Level 1-2 router has two IS-IS databases. The Level 1 database is used for routing to destinations within the router's configured area. The Level 2 database is used to route between destinations in different areas.

An Area Border Router (ABR).
By default, all routes are advertised into all OSPF areas. This includes interarea OSPF routes and external routes that have been injected into OSPF. By default, IS-IS does not advertise interarea or external routes into an area, but injects a default route.

Redistribution of Level 2 routes into an area as Level 1 routes.
An OSPF interface metric is determined from the interface bandwidth. By default, all IS-IS interface metrics are equal to 10.

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A narrow metric uses 6 bits for the interface metric and 10 bits for the path metric. A wide metric uses 24 bits for the interface metric and 32 bits for the path metric.

► IBGP is the protocol used between routers in the same autonomous system. EBGP is the protocol used between routers in different autonomous systems.

► IBGP routes must be synchronized before they can be transferred to the IP routing table (unless synchronization is disabled).

► EBGP sets the next hop attribute to the IP address of the interface used to communicate with the EBGP peer. The next hop attribute is not modified when an IBGP router advertises a prefix to an IBGP peer if the prefix was learned from an EBGP neighbor.

► EBGP advertises all prefixes learned from an EBGP neighbor to all other EBGP neighbors. IBGP routers do not advertise prefixes learned from one IBGP neighbor to another IBGP neighbor.

If a router has more than one route to the same IP prefix, the best path is the one with the shortest AS_PATH (assuming other BGP attributes are equal).

If a router has more than one route to the same IP prefix, the best path is the one with the highest WEIGHT value.

WEIGHT has only local significance and is not advertised to BGP peers.

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If a router has more than one route to the same IP prefix, the best path is the one with the highest LOCAL_PREF (assuming the WEIGHT attribute for the routes is equal).
The LOCAL_PREF attribute is advertised throughout the autonomous system.
MED is used to prefer a path into an autonomous system. A lower MED value is preferred.
WEIGHT, LOACL_PREF, AS_PATH, MED
► Using the network command to transfer a router from the IP routing table to the BGP routing table

► Redistributing routes from the IP routing table to the BGP routing table

► Learned from a BGP neighbor

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BGP checks the NEXT_HOP attribute to determine if the NEXT_HOP is accessible or in the IP routing table.

Synchronization is a property of IBGP. An IBGP router will not accept a prefix received from an IBGP neighbor if the prefix is not already in the IP routing table.

Route reflector and confederation.

BGP uses the AS_PATH attribute for loop detection. If a router sees its own AS number in a BGP advertisement, the advertisement is dropped. IBGP routers have the same AS number so the AS number cannot be used for loop detection. IBGP neighbors will not advertise prefixes learned from one IBGP neighbor to another IBGP neighbor; therefore, a full mesh is required.

When a summary address is created with an IGP (EIGRP, OSPF, and IS-IS), the specific routes of the summary are not advertised. BGP advertises the summary, and all the specific routes of the summary unless they are specifically suppressed.

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RIP version 1 and IGRP are classful protocols and do not advertise subnet mask information. RIP version 2 has a limited network diameter of 15 hops. EIGRP, OSPF, and IS-IS use computational intensive algorithms for determining a shortest path. BGP relies on simple techniques for best path selection and loop detection, and can handle the number of network prefixes required for Internet routing.

Well-known mandatory, well-known discretionary, optional transitive, and optional nontransitive.

Unicast IP packets are forwarded based on the destination IP address. Multicast packets are forward based on the source IP address. If a multicast packet is received on the interface used to send a unicast packet back to the source, the multicast packet is forwarded to multicast neighbors. If the multicast packet is received on an interface that would not be used to send a unicast IP packet back to the source, the packet is discarded.

Dense mode multicast assumes all multicast neighbors want to receive all multicast traffic unless the neighbors have specifically pruned the traffic. Sparse mode multicast assumes multicast neighbors do not want to receive multicast traffic unless they have asked for it. Dense mode uses source-based delivery trees while sparse mode uses shared delivery trees where traffic is first sent to an RP.

The base Ethernet multicast address is 01 00 5E 00 00 00. The first byte of the IP multicast address is not used. If the second byte is greater than 127, subtract 128, giving a value of 0. The third and fourth bytes of the IP address are used as is after converting to hex. Their values, in hexadecimal, are 40 and 0C. So the Ethernet multicast address for the IP multicast address 227.128.64.12 is 01 00 5E 00 40 0C.

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The low order 32 bits of the IP address determine the multicast Ethernet address. The first four bits are always 1 1 1 0 and the next five bits can be anything. Therefore, the IP multicast addresses that map to the multicast Ethernet address of 01 00 5E 00 40 0C are

1110 0000 0000 0000 0100 0000 1100 = 224.0.64.12

1110 0000 1000 0000 0100 0000 1100 = 224.128.64.12

1110 0001 0000 0000 0100 0000 1100 = 225.0.64.12
Multicast forwarding decisions are based on the entries in the unicast IP routing table. Multicast is not dependent on how the unicast IP routing table was built; you can use any dynamic interior routing protocol, static routes, or a combination of the two.
CGMP and IGMP Snooping

Two or more RPs are configured with the same IP address. The IP addresses of the RPs are advertised using a unicast IP routing protocol. Each multicast router chooses the closest RP. If an RP fails, the routers switch to the next nearest RP after the unicast IP routing protocol converges. The MSDP is used between RPs to exchange active multicast source information.

224.0.0.0–239.255.255.255

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Used with PIMSM Auto-RP and version 2. If the RPs fail, the router reverts to dense mode.

A RP is the focal point for multicast traffic. Traffic is forwarded to the RP from multicast sources. The RP then forwards traffic to multicast receivers.

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