CCNP - BSCI Exam cram

(Exam: 642-801)

CCNP-BSCI (Building Scalable Cisco Internetworks) exam is a requirement towards obtaining CCNP certification. Skills measured are: Designing and implementing complex routed WANs including EIGRP, OSPF, BGP, and IS-IS. Valid CCNA certification is a pre-requisite for obtaining CCNP certification.

To be CCNP certified, the following exams need to be successfully completed:

Exam	Exam Code	Study material covering exam objectives
BSCI Exam	642-801	Building Scalable Cisco Internetworks or BSCI
Switching Exam	642-811	Building Cisco Multi-layer Switched Network or BCMSN
Remote Access Exam	642-821	Building Cisco Remote Access Networks
Support Exam	642-831	Cisco Internetwork Troubleshooting

Alternatively, one can take the following exams to obtain CCNP certification:

Exam	Exam Code	Study material covering exam objectives
Foundations Exam	640-841 *retired"	Building Scalable Cisco InterNetworks (Corresponds to 640-901 exam)
		Building Cisco Multi-layer Switched Network. (Corresponds to 640-604 exam)
		Building Cisco Remote Access Networks. (Corresponds to 640-605 exam)
Support Exam	640-606 "retired"	Cisco Internetwork Troubleshooting (CIT).

The BSCI exam is of 75min duration and there will be approximately 65 questions. You need to score 690 or more to pass the exam. Visit the official website here.

1. Scalable networks:

The key 5 characteristics of Scalable Internetworks are:

Reliable and available: An internetwork is usually up for 24 hours a day and seven days a week.
Efficient: Efficiency means optimization of resources keeping in view available bandwidth. An internetwork should have less amount of overhead traffic, such as broadcasts, routing updates etc.
Responsive: It is necessary that the internetwork meet QoS requirements for different protocols. Cisco IOS has been developed keeping in view the QoS demands. Different protocols may require different QoS standards.
Adaptable: An internetwork should be able to accommodate variety of networks and protocols. The available protocols may include for example, TCP/IP, IPX, and SNA. An adaptable internet should be able to accommodate legacy as well as more recent technologies such as VOIP.
Accessible and Secure: An internet should be accessible by using different access methods, such as dial-up, dedicated, switched connections. At the same time, it should provide secure environment.

2. The typical three-layer hierarchical internetworking model consists of the following:

Core layer: Core layer is responsible to provide an optimal and reliable transport structure. The core layer is the backbone network of the entire internetwork and may include LAN and WAN backbones. Core layer usually consists of fully redundant paths with technologies such as FDDI, Fast Ethernet, and/ or ATM.
Distribution layer: Distribution layer is responsible to provide access to the internetwork as well as to the servers. Distribution layer sits between the Core layer and the Access layer. The policies such as ACLs are implemented at the distribution layer. Distribution layer is also known as workgroup layer.
Access layer, provides the users, access to the resources on internetwork.

In real world, a single device may be functioning at both Access layer as well as distribution layer. This is true for even Core layer.

3. Network segmentation:

Network congestion can be addressed by segmentation of the network. Network segmentation, also called micro segmentation, can be done by using:

Bridges,
Routers, and
Switches.

The primary purpose of segmentation is to reduce congestion in the network.

4. Bridges and switches forwards all broadcasts, which puts extra load on the network. In other words, though bridges divide the network into different collision domains, the broadcast domain remain only one. This increases the overhead on the network.

5. The Cisco IOS features that allow reduction in bandwidth are:

Access Control Lists: ACLs are used to permit or deny protocol update traffic, data traffic, and broadcast traffic. Cisco access lists are available for IP, IPX, and AppleTalk protocols.
Snapshot routing: Snapshot routing can reduce WAN costs, by exchanging the routing table at predefined intervals. The routing tables for the distance vector protocols are kept frozen until the next update occurs. Snapshot routing is used only on distance vector protocols such as IP RIP. Snapshot routing is widely used on ISDN lines.
Compression over WANs: Cisco IOS supports TCP/IP packet header, as well as data compression. Link compression is also supported, that compresses both header and data information in packets across point to point connections.
DDR (Dial on Demand Routing): DDR are useful when the traffic flow is not continuous in nature. In DDR, channel is created only after intended traffic is detected by the router, by dialing the destination.
Switched network access: Switched networks, such as Frame Relay, X.25 can share the bandwidth by establishing virtual circuits.
Optimization of routing table size: Routing table entries consume bandwidth and processing power. These entries can be reduced by techniques such as route summarization, and incremental updates.

6. Snapshot routing builds routing table based on a snapshot of a dynamic routing table available when the network is active. The snapshot routing table is used until another activity occurs on the network, at which time the routing table is rebuilt. No routing information is exchanged when the network is quiet. Snapshot routing can be applied to distance vector protocols such as IP RIP, IGRP, IPX RIP, and RTMP.

7. Cisco IOS supports the following queuing methods:

Weighted fair-queuing: This is an automatic queuing method that provides fair bandwidth to all network traffic.
Priority queuing: Here, one particular type of traffic is given priority over all other types of traffic. Thus this particular traffic, for which priority is given, is assured of bandwidth. All other types of traffic do not have assured bandwidth.
Custom queuing: Here, each traffic type gets a pre-allocated bandwidth. Certain types of traffic can be allocated higher bandwidth depending on the requirement.

8. RIP

- RIP (and IGRP) always summarizes routing information by major network numbers. This is called classful routing.

- IP RIP based networks send the complete routing table during update. The default update interval is 30 seconds.

- RIP version 2 is a classless routing protocol, where as RIP version 1 (RIP 1) is a classful routing protocol. The disadvantage of classfull routing is that some address space may be wasted. In classless routing, routing protocols exchange the subnet mask information during periodic routing updates. This allows variable subnet masks to be used in the network, allowing better use of address space. For example, a WAN link may need only two IP addresses. If you use classless routing protocol with, say 6 bits for subnetting (62-2 subnets), only 2 subnet addresses are utilized and the remaining become wasted. On the other hand, if you use classless routing protocol, Variable Length Subnet Mask (VLSM) can be used within the network, giving only 2 valid addresses for the WAN link, thus saving valuable address space. (If you are using IP addresses, address space involves IP addresses).

9. Metric limit for link-state protocols is 65,533.

10. Convergence is the term used to describe the state at which all the internetworking devices, running specific routing protocol, are having the same information about the internetwork in their routing tables. The time it takes to arrive at common view of the internetwork is called Convergence Time.

11. Distance vector protocol depends only on Hop count to determine the nearest next hop for forwarding a packet. One major disadvantage is that this may not always represent the best route. For example, if you have a destination connected through two hops via T1 lines, and if the same destination is also connected through a single hop through a 64KBPS line, RIP assumes that the link through 64KBPS is the best path!

12. There are broadly three types of routing protocols:

Distance Vector (Number of hops) - Distance vector routing determines the direction (vector) and distance to any link in the internetwork. Typically, the smaller the metric, the better the path. EX: Examples of distance vector protocols are RIP and IGRP. Distance vector routing is useful for smaller networks. The limitation is that any route which is greater than 15 hops is considered unreachable. One important thing that differentiates distance vector with Link state is that distance vector listens to second hand information to learn routing tables whereas, Link state builds its routing tables from first hand information. Distance vector algorithms call for each router to send its entire routing table to each of its adjacent neighbors.

Link State Routing: Link State algorithms are also known as Shortest Path First (SPF) algorithms. SPF recreates the exact topology of the entire network for route computation by listening at the first hand information. Link State takes bandwidth into account using a cost metric. Link State protocols only send updates when a change occurs, which makes them more attractive for larger networks. Bandwidth and delay are the most heavily weighed parts of the metric when using Link-State protocols. EX: OSPF and NLSP.

Benefits of Link State protocols:

1. Allows for a larger scalable network

2. Reduces convergence time

3. Allows “super netting”

3. Balanced Hybrid - Balanced Hybrid combines some aspects of Link State and Distance Vector routing protocols. Balanced Hybrid uses distance vectors with more accurate metrics to determine the best paths to destination networks. EX: EIGRP.

13. The default administrative distances are as below:

Type of protocol	Administrative distance
Directly connected	0
Static route	1
EIGRP Summary	5
External BGP	20
EIGRP	90
IGRP	100
OSPF	110
ISIS	115
RIP	120
Unreachable	255

14. IGRP, EIGRP: IGRP and EIGRP are proprietary of Cisco. These two protocols use composite metric to determine the best path to a remote network.

- IGRP (as well as EIGRP) use the following components as metrics:

1. Delay: Calculated by adding up the delay along the path to the next router.

2. Reliability: This is representative of how many errors are occurring on the interface. The best reliability value is 255. A value of 128 represents only 50% reliability.

3. Load: Load metric also has a range from 1 to 255. If a serial link is being operated at 50% capacity, the load value is 255X0.5 or 12.5. Lower load value is better.

4. MTU: Stands for Maximum Transmit Unit size, in bytes. Ethernet and serial interface has a default MTU of 1500. Larger MTU size means that the link is more efficient.

5. Bandwidth: The bandwidth is specified in Kbps. Larger the bandwidth, better the link.

EIGRP (as well as IGRP) uses Bandwidth and Delay as default criteria to determine the best path.

- show ip route eigrp: Displays the current EIGRP entries in the routing table.

- Show ip eigrp traffic: This command can be used to learn the number of EIGRP packets sent and received.

- The neighbor table in EIGRP include the following fields:

1. Neighbor address: This is the network layer address of the neighbor router.

2. Queue: This represents the number of packets waiting in queue to be sent.

3. Smooth Round Trip Time (SRTT): This represents the average time it takes to send and receive packets from a neighbor. This timer is used to determine the retransmit interval (RTO).

4. Hold Time: This is the period of time that a router will wait for a response from a neighbor. If there is no response at the end of this time period, the link is considered unavailable.

15. Hello packets:

- The types of router protocols that use "Hello" packets are EIGRP, IS-IS, and OSPF.

16. Cisco IOS commands:

1. Show IP protocol: This command will show information on RIP timers including routing update timer (30sec default), hold-down timer (default 180sec). It also displays the number of seconds due for next update (this is fraction of update timer). This command also gives the network number for which IP RIP is enabled, Gateway, and the default metric.

2. Show IP route: This command will display the IP routing table entries. In addition, it displays the Gateway of last resort (if one is assigned). It also displays the codes used for various types of routes. Some of the important codes are:

C: directly connected;

S: Statically connected

I : IGRP

R : RIP

3. show IP interface: This command shows you interface-wise information such as IP address assigned to each interface, whether the interface is up, MTU etc.

4. Debug IP RIP: Debug IP RIP will turn the RIP debugging ON. This will display a continuous list of routing updates as they are sent and received. This leads to lot of overhead, which is the reason that you use "undebug ip rip" to turn-off debugging as soon as you finish with debugging.

5. The command "no router rip" is used for removing all rip entries from the router.

6. The command

i. clear ip bgp *

clears all the entries from the BGP routing table and reset BGP sessions. This command is used after every configuration change to ensure that the change is activated and that peer routers are informed.

ii. Another command,

clear ip bgp <address>

ex: clear ip bgp 172.31.0.0 removes the specified network from the BGP table.

17. For IGRP routing, you need to provide the AS (Autonomous System) number in the command. Routers need AS number to exchange routing information. Routers belonging to same AS exchange routing information.

18. IGRP:

- IGRP update packet is sent every 90 seconds by default. This is 30 Sec for RIP.

- By giving the command "show ip route igrp", we can see the routes found by IGRP. A route discovered by IGRP is denoted by letter "I" before start of the entry.

- The following three types of routes are recognized by IGRP:

1. Interior: Interior routes are those that are directly connected to a router interface.

2. System: Routes advertised by other IGRP neighbors within the same autonomous system (AS).

3. Exterior: These are the routes learned from a different Autonomous System number (ASN).

19. Private Internet addresses:

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space your use for private networks:

10.0.0.0 - 10.255.255.255

172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255

20. There are three ways a router learns how to forward a packet:

1. Static Routes - Configured by the administrator manually. The administrator must also update the table manually every time a change to the network takes place. Static routes are commonly used when routing from a network to a stub (a network with a single route) network.

The command is

ip route network mask address/interface [distance]

ex: ip route 165.44.34.0 255.255.255.0 165.44.56.5

Here, 165.44.34.0 is the destination network or subnet

255.255.255.0 is the subnet mask

165.44.56.5 is the default gateway.

2. Default Routes - The default route (gateway of last resort) is used when a route is not known or is infeasible. The command is

ip route 0.0.0.0 0.0.0.0 165.44.56.5

The default gateway is set to 165.44.56.5

3. Dynamic Routes - As soon as dynamic routing is enabled, the routing tables are automatically updated. Dynamic routing uses broadcasts and multicasts to communicate with other routers. Each route entry includes a subnet number, the interface out to that subnet, and the IP address of the next router that should receive the packet. The commands to enable rip are:

router rip

network <major network number>.

21. OSPF:

1. An OSPF area is a collection of networks and routers that has the same area identification.

2. The following are the types of OSPF routers:

i. Internal router: An internal router has all the interfaces in the same area. All internal routers maintain same link state databases.

ii. Backbone router: Backbone routers reside on the perimeter of Area 0, with at least one interface connected to backbone (Area 0).

iii. Area Border Router (ABR): ABRs are routers that have interfaces attached to multiple areas. It may be noted that these routers maintain separate link-state databases for each area that they are connected. They are capable of routing traffic destined for or arriving from other areas.

iv. Autonomous System Boundary Router (ASBR): This router has at least one interface to the external network (another autonomous system). This autonomous network can be non-OSPF. ASBRs are capable of route redistribution. Redistribution is the ability of a router to import routing information from non-OSPF networks, and distribute the same in OSPF network for which it is responsible and visa versa.

3. LSA Types:

i. LSA Type 1: Router link entry, generated by all routers for each area to which it belongs. These are flooded within a particular area.

ii. LSA Type 2: Network link entry, generated by designated router (DRs). Type 2 LSAs are advertised only to routers that are in the area containing the specific network.

iii. LSA Type 3 and Type 4: Summary link entry, these LSAs are generated by area border routers (ABRs). These are sent to all routers within an area. These entries describe the links between the ABR and the internal routers of an area. These entries are flooded throughout the backbone area and to the other ABRs.

iv. LSA Type 5: Autonomous System External Link Entry, these are originated by ASBR. These entries describe routes to destinations external to the autonomous system. These LSAs are flooded throughout the OSPF autonomous system except for stubby and totally stubby areas.

4. The sequence of steps followed in OSPF operation are as below:

1. Establish router adjacencies

2. Elect DR and BDR

3. Discover Routes

4. Choose appropriate routes for use

5. Maintain routing information.

5. The command "show ip ospf database" displays the contents of the topological database maintained by the router. This command also displays router id and the ospf process id.

6. show ip ospf interface can be used to check whether the interfaces have been configured properly. The command also gives the timer intervals, including hello intervals, and neighbor adjacencies.

7. OSPF keeps up to six equal-cost route entries in the routing table for load balancing.

8. OSPF uses Dijkstra algorithm to calculate lowest cost route. The algorithm adds up the total costs between the local router and the each destination network. The lowest cost route is the preferred route when there are multiple paths to a given destination.

9. OSPF has the following advantages over Distance Vector protocols such as RIP:

1. Faster convergence: OSPF network converges faster because routing changes are flooded immediately and computed in parallel.

2. Support for VLSM: OSPF supports VLSM. However, please note that RIP version2 also supports VLSM.

3. Network Reachability: RIP networks are limited to 15 hops. On the other hand, OSPF has practically no reachability limitation.

4. Metric: RIP uses only hop count for making routing decisions. This may lead to poor efficiency in some cases. For example, that a route is nearer but is very slow compared to another route with plenty of bandwidth available but few more hops away. OSPF uses "cost" metric to choose best path. Cisco uses "bandwidth" as metric to choose best route.

5. Efficiency: RIP uses routing updates every 30 seconds. OSPF multicasts link-state updates and sends the updates only when there is a change in the network status

10. The path cost in OSPF network is calculated using bandwidth. The formula used is [10 <8> divided by Bandwidth]. For example, the cost of a 56kbps serial link is 1785. The default cost of a 10mbps Ethernet is 10.

22. When a serial line is configured on a Cisco router, the default bandwidth is 1.544Mbps. If the line is slower speed, "bandwidth" command can be used to specify the real link speed. The cost of the link will then automatically correspond to the changed value.

23. You must manually configure a static route to configure DDR (Dial on Demand Routing). DDR is widely used as a backup route, in case of failure of primary link.

24. Route Summarization:

Route summarization is calculated as below:

Step 1:

1. Take the first IP: 172.24.54.0/24: 172.24. 0 0 1 1 0 1 1 0.0

2. Take the second IP: 172.24.53.0/24: 172.24. 0 0 1 1 0 1 0 1.0

Note that we are not really concerned about the octets that have equal decimal values. This is because they don’t come into play while calculating summarization route, in this case.

Step 2:

Count the number of bits in the third octet that are aligned (or lined up) with same values. In this case 6 bits are lined up in the third octet. The summarization route is calculated by adding this number (6) to the octets preceding the third (first and second octets).

Therefore, the number of bits in the summarized route is 8+8+6 = 22

Step 3:

Calculate the decimal equivalent for third octet with 6 bits as given in the matching binary. That is 0 0 1 1 0 1 x x. Note x is because it corresponds to non matching binary number. It is equal to 128*0 + 64*0 + 32*1 + 16*1 + 8*0 + 4*1 or 32+16+4 or 52.

Therefore, the summarized route is:

172.24.52.0/22

25. While evolving a network addressing scheme for an organization, you need to assign a different network number for each subnet. Also, you need to set aside one network number for each WAN connection.

26. Representing a subnet mask with / notation:

Consider an IP subnet mask of 255.255.255.128. The same be represented as /25. This is arrived at, by taking the binary equivalent of 255.255.255.128 (= 11111111.11111111.11111111.10000000). Count the number of ones’, there are 25 of them. Therefore, the same can be written as /25.

27. The following are link state routing protocols:

IPX NLSP

IS-IS

IP-OSPF

28. OSPF - LSA, LSR, and LSUs:

1. LSA (Link State Advertisement): LSAs are included in the database description packets (DDPs or DBDs). LSA entries include link-state type, the address of the advertising router, the cost of the link, and the sequence number.

2. LSR ( Link State Request): When a slave router receives a DDP (Database Description Packet), it sends an LSAck packet. Then it compares the received information with its own information. If the DDP has more recent information, the slave router sends a link-state request (LSR) to the master router.

3. LSU ( Link State Update): LSU packet is sent in response to LSR (Link-State Request) packet that is sent from a slave router to a master router. LSU contains complete information about the requested entry.

4. In an OSPF environment,

1. A DDP (Data Description Packet) is used during the exchange protocol and includes summary information about link-state entries.

2. A hello packet is used during the hello process and includes information that enables routers to establish neighbor relationship.

3. An internal router is a router that resides within an area.

29. Important features of stub area are:

1. A stub area reduces the size of the link-state database to be maintained in an area, which in turn result in less overhead in terms of memory capacity, computational power, and convergence time.

2. The routing in Stub and totally Stubby areas is based on default gateway. A default route (0.0.0.0) need to be configured to route traffic outside the area.

3. The stub areas suited for Hub-Spoke topology.

4. Area 0 is not configured as Stubby or totally Stubby. This is because stub areas are configured mainly to avoid carrying external routes, whereas Area 0 carries external routes.

30. EIGRP:

Some of the important terms used in Enhanced IGRP are:

1. Successor: A route (or routes) selected as the primary route(s) used to transport packets to reach destination. Note that successor entries are kept in the routing table of the router.

2. Feasible successor: A route (or routes) selected as backup route(s) used to transport packets to reach destination. Note that feasible successor entries are kept in the topology table of a router. There can be up to 6 (six) feasible successors for IOS version 11.0 or later. The default is 4 feasible successors.

3. DUAL (Diffusing Update Algorithm): Enhanced IGRP uses DUAL algorithm to calculate the best route to a destination.

31. BGP:

- Internet Assigned Numbers Authority (IANA) is responsible for assigning BGP autonomous system numbers.

1. The assignable BGP autonomous system numbers are from 1 to 65,535 (I.e. 65,535 in total). Autonomous system numbers are of 16 bit length. There are 2 ^ 16 = 65536 -1 possible ASNs. ASN of all 0s is not assigned. Out of this, the Internet Assigned Numbers Authority (IANA) has reserved the following block of AS numbers for private use: 64512 through 65535.

2. External BGP (eBGP) is used to establish session and exchange route information between two or more autonomous systems. Internal BGP (iBGP) is used by routers that belong to the same Autonomous System (AS).

3. Routers running BGP in an AS use network Policy to choose the best path. Metrics are not used in BGP. Remember that Internet is made of autonomous systems (AS) that are connected together based on Policies specific to each AS. Also, AS numbers (ASN) are assigned by AINA and are unique over the Internet. In an internet (not big I) the ASNs can be assigned by the corporation itself that is implementing internet.

4. The following are the four possible message types in a BGP header:

Type 1: OPEN message - This is the first message sent after TCP session is established.

Type 2: UPDATE message - An UPDATE message contains a new route or a route to be withdrawn or both. Note that only one new route can be advertised with one UPDATE message.

Type 3: NOTIFICATION message - this message is sent if an error occurs during a BGP session. This message can be used to troubleshoot the problem.

Type 4: KEEPALIVE message - KEEPALIVE message is used to confirm that the connection between the neighboring routers is still active.

5. Command to set the router RouterA to autonomous system number 1340:

The correct syntax for the command is:

RouterA(config)#router bgp 1340

where 1340 is the AS number which can have a value between 1 and 65535 in an internetwork.

6. Port number 179 is used to establish a session between two routers running BGP.

7. Well-Known mandatory attributes must appear in all BGP update messages. The well-known mandatory messages are:

1. AS_PATH: BGP messages carry the sequence of AS numbers indicating the complete path a message has traversed.

2. NEXT_HOP: This attribute indicates the IP address of the next-hop destination router.

3. ORIGIN: This attribute tells the receiving BGP router, the BGP type of the original source of the NLRI information.

8. Any two routers that have formed a TCP connection in order to exchange BGP routing information are called peers, or neighbors. BGP peers initially exchange their full BGP routing tables. After this exchange, routing table changes are sent as incremental updates. BGP keeps a version number of the BGP table, which should be the same for all of its BGP peers. The version number changes whenever BGP updates the table, likely due to routing information changes. Keep alive packets are sent to ensure that the connection is alive between the BGP peers.

9. show ip bgp neighbors

This is a very useful command in troubleshooting BGP connections. When the connection is established, the peer/ neighbor router exchanges BGP information. If a TCP connection (BGP session) is not established, a BGP router can not exchange any BGP routing information with the adjacent router.

10. Few recommended scenarios, where you use BGP are:

1. Connect two or more ISPs

2. The traffic flow out of your network need to be managed to suit the requirements of your organization.

3. The traffic need to be sent through one AS to get to another AS.</