THE THREE LAYER NETWORK DESIGN

The three layer network design models are useful because they facilitate modularity such as? (page 12)

In network services, the new network model provides remote services quickly and easily to all users. (page 13)

What are the three types of network services? (page 13)

Local services.... (page 14)

Which service is close to users but not on the same network or subnet as the users? (page 15)

Remote services might not have to cross the backbone. (page 15)

When servers that host enterprise services are placed close to the backbone, all users would be different distances from the servers, so most user data would have to cross the backbone to get to the services. (page 16)

Enterprise services are provided to..... (page 16)

The Open Systems Interconnection (OSI) model has seven layers, each of which specifies functions that enable data to be transmitted from host to host on an internetwork. (page 17)

The presentation layer is responsible for dialogue control. (page 18)

The transport layer is responsible for end-to-end connection. (page 18)

In the OSI reference model, each layer encapsulates the layer immediately below it as the data flows up the protocol stack. (page 19)

The logical communication that happens at each layer of the OSI reference model doesn’t involve many physical connections because the information each protocol needs to send is encapsulated in the layer of protocol information beneath it. (page 19)

What are the upper layers of the OSI model? (page 20)

The upper layers are designed to move packets, and the lower layers deal with the types of applications. (page 20)

In the Application layer, the common functions are..... (page 21)

When data is transmitted between different types of computer systems, the _________________ negotiates and manages the way data are represented and encoded. (page 22)

The presentation layer is used for encryption and decryption. (page 22)

The Session layer provides coordination of the communications in an orderly manner. (page 23)

The Session layer marks significant parts of the transmitted data with checkpoints to allow for fast recovery in the event of a connection failure. (page 23)

Which layer is not often used or services within this layer are sometimes incorporated into the transport layer? (page 23)

The Transport layer is responsible for overall node - to - node validity and integrity of the transmission. (page 24)

"OSI transport services" include layers 1 through 4 , collectively responsible for delivering a complete message or file from sending to receiving station without error. (page 24)

The ___________ is also the switching function of the dial - up telephone system. (page 26)

In the Data Link layer, the transmitted bits are divided into frames. (page 27)

Layers 1 and 2 are not always required for every type of communications. (page 27)

The Physical layer has no understanding of the meaning of the bits, but deals with the electrical and mechanical characteristics of the signals and signaling methods. (page 28)

The Routing Information Protocol is a ____________routing protocol that is the routing protocol that is responsible for early Internet connectivity. (page 31)

RIP sends ______ data packets to exchange routing updates when the network topology changes and at regular timed intervals. (page 31)

RIP routing tables are updated with the best path selection. (page 31)

What are the several factors that provide routing stability on a RIP network? (page 32)

Poison reverse updates are used to stop larger routing loops in a RIP network. (page 32)

Split horizons are used as a process to not send information about a route from the direction from which it came. (page 32)

A router configured with RIP will send out periodic updates to the internetwork every 40 seconds. (page 33)

In addition, anytime a topology change occurs, all the RIP enabled routers won't send out routing table updates. (page 33)

What are the three types of timers that are used in a RIP network? (page 34)

Which timer is used when RIP routers send the entire routing table to its neighbouring routers? (page 34)

If a specific route is not heard from within a specified amount of time (default is 180 seconds), the routers assume that the route is no longer available. Which timer is used for this? (page 34)

If a route has not been heard from for 90 seconds ( default value) after the Invalid timer has been sent, the router will inform its neighbouring routers, and then the route is flushed from the router's routing table. This is called the Flush timer. (page 34).

What are the advantages of RIP? (page 35)

RIP v2 was developed to expand the amount of information carried in an RIP message. (page 36)

RIP v2 doesn't contain any additional security features such as authentication. (page 36)

The default Cisco IOS is configured to receive RIP vl and RIP v2 packets, but only sends RIP v2 packets. (page 36)

What are the RIPv2 advantages? (page 37)

OSPF is a ___________ protocol that was originally developed to meet the needs of larger heterogeneous enterprise networks. (page 39)

OSPF networks operate within an Autonomous System (AS ),which is a collection of networks that share a common routing strategy. (page 39)

OSPF Areas...... (page 40)

Areas are a group of routers that route from the same topology database and maintain the same routing algorithms. (page 40)

Area 1 is the backbone area required in an OSPF network. (page 40)

Stub areas are OSPF areas that have internal routes but no external routes other than a default route. (page 40)

What are the four types of OSPF routers that can be present in an OSPF network? (page 42)

OSPF propagates only updates to the internetwork, not full routing tables during a network update. (page 42)

OSPF routers use the SPF (Shortest Path First) algorithm to calculate the longest path to the destination. (page 43)

The SPF (shortest path first) algorithm is frequently called the Dijkstra algorithm in recognition of the creator of the algorithm. (page 43)

In OSPF, the calculations on least cost populate the link - state database that is resident on each router in the internetwork. (page 43)

What are the three important components to the OSPF protocol? (page 44)

The Hello protocol processes the election of Designated Routers (DRs). (page 45)

Hello packets are also used as keep - alive messages to maintain the neighbour relationship with other routers in the area. (page 45)

With OSPF, the DR is responsible for generating link - state advertisements (LSAs) for the entire internetwork. (page 45)

The Exchange protocol is used to synchronize the routing database for the internetwork. (page 46)

The Flooding protocol distributes the link - state database whenever a change occurs in the internetwork. (page 46)

In OSPF, a router that changes a link - state will send a flooding packet to inform the other routers of the change or changes, this is flooded out to all of the routers interfaces. (page 46)

OSPF advantages.... (page 47)

Intermediate System to Intermediate System (IS - IS) is a ____________ interior gateway routing protocol. (48)

With IS-IS, there are several concepts that are important and unique. (page 48)

Level 1 routers route all information to a Level 2 router in their area. (page 48)

Only Level 2 routers can communicate with external routers outside of the routing domain. (page 48)

What are three main protocols in the ISO suite? (page 49)

What are the IS-IS protocol advantages? (page 50)

Netware Link Services Protocol is a _________ routing protocol developed for Novell NetWare internetworks. (page 51)

NLSP was developed by Novell to overcome some limitations of IPX RIP (IPX Routing Information Protocol) and SAP (Service Advertisement Protocol). (page 51)

NLSP advantages..... (page 51)

The several key concepts concerning NLSP routing include: (page 52)

What are the NLSP routing levels? (page 53)

NLSP routers exchange Hello packets to determine neighbour reachability information (adjacency information). Adjacency information is stored in the adjacency database. (page 54)

In NLSP, LSPs are combined into one database, the link - state database. (page 54)

When an NLSP router detects a topology change, the router creates a new LSP and sends it to its neighbour router. (page 55)

What are the two types of NLSP receipt confirmations? (page 55)

NLSP advantages..... (page 56)

Border Gateway Protocol is a ________ exterior routing protocol that is in prominent use today on the Internet and was developed to replace the old exterior gateway protocol, Exterior Gateway Protocol (EGP). (page 57)

The main function of the BGP is to perform interdomain routing in an IP network , and it addresses the task of path determination. (page 57)

In a BGP network, certain routers act as BGP speakers to learn about all the multiple paths on the internetwork. (page 57)

What are the three types of routing that BGP performs? (page 58)

BGP uses routing metrics to maintain the network topology routing tables. (page 59)

What are the four main message types in BGP? (page 60)

BGP advantages...... (page 62)

Interior Gateway Routing Protocol is a Cisco - specific protocol that operates as a __________ routing protocol. (page 63)

What are the three types of routes advertised within an IGRP network? (page 63)

The routing metric for IGRP is a combination of: (page 64)

To reduce the possible occurrence of routing loops, IGRP uses split horizon, poison reverse, hold - down intervals, and flush updates. (page 64)

The Enhanced Interior Gateway Routing Protocol (EIGRP) is a ____________ interior gateway routing protocol that is used exclusively in Cisco networks. (page 65)

In EIGRP, DUAL is a specification for routers to store neighbouring information to allow quick routing updates and network convergence. (page 65)

What EIGRP features are similar and different to IGRP? (page 66)

In EIGRP, hello messages are sent to neighbors every 5 seconds (60 seconds in most WANs). (page 67)

EIGRP can load balance across six unequal cost paths to a remote network (4 by default). (page 68)

What are the EIGRP key concepts? (page 69)

A Successor route is used by EIGRP to forward traffic to a destination. (page 71)

In EIGRP, Successor routes may be backed up by a feasible successor route. (page 71)

In EIGRP, Successor routes are stored in both the topology table and the routing table. (page 71)

Packet Formats - There are five types of packets in an EIGRP network . These include: (page 72)

In EIGRP, Routes are tagged with interior or exterior route information. (page 72)

In EIGRP, what are the new components implemented as an improvement over IGRP? (page 74)

In EIGRP, If there is no feasible successor available, a new route is computed and a feasible successor is chosen. (page 75)

An EIGRP implementation can be done incrementally, with no adverse effect on existing routes. (page 78)

IGRP routes are treated as external routes by EIGRP and are easily configured with the new EIGRP networks. (page 78)

EIGRP is compatible and can redistribute routes for: (page 78)

EIGRP advantages...... (page 79)

The RIP v2 extensions are listed in the following: (page 81)

The Subnet Mask field enables the use of variable - length subnet masks (VLSMs) and qualifies RIP v2 as a classless routing protocol. (page 81)

RIP v2 updates to other RIP v2 inter - routers by multicasting. (page 82)

What are the four features that are the most significant new features added to RIP v 2? (page 83)

RIP v2 allocates a 4 - octet field to associate a subnet mask to a destination IP address. (page 85)

Multicasting is a technique for simultaneously advertising routing information to multiple RIP or RIP v 2 devices. (page 87)

RIP v2 handles updates in a flexible manner such as: (page 89)

RFC 1723 defines a compatibility switch with four settings, which allows versions 1 and 2 to interoperate, such as: (page 89)

The true defining characteristic of classless routing protocols is the capability to carry subnet masks in their route advertisements. (page 91)

Classful routing protocols can distinguish between an all - zeros subnet, for example 172.16.0.0, and the major network number 172.16.0.0. (page 91)

The authentication process for RIP v2 announcements uses the first route entry in the RIP message to store authentication information. (page 92)

To indicate authentication, the Family Identifier field is set to: (page 92)

In RIPv2 authentication, the first route entry must be used, leaving a maximum of _________ in a RIP v2 authenticated announcement. (page 92)

In RIPv2 authentication, the Authentication Type field, normally used as the Route Tag field for a route, indicates the type of authentication being used. (page 92)

In RIPv2, simple password authentication uses the Authentication Type value of 0x00 - 01. (page 92)

In RIPv2 authentication, the _______ after the Authentication Type are used to store the authentication value. (page 92)

MD5 is a one - way message digest or secure hash function, produced by RSA Data Security, Incorporated. (page 93)

MD5 computes a ________ hash value from a plain text message of arbitrary length and a password. (page 93)

RIP v2 can be used in networks that require either support for authentication and variable - length subnet masks. (page 94)

RIP v2 continues to maintain multiple routes to any given destination in its routing tables. (page 95)

In the event a route becomes invalid, the RIP v2 node does not know any other routes to the destination of the failed route. (page 95)

RIP v2 continues to rely on counting to infinity as a means of resolving certain error conditions within the network. (page 96)

RIP v2 doesn't depend on timers to generate updates. (page 96)

In RIPv2, after a route cost is incremented to 16, that route becomes invalid, and the destination is considered unreachable. (page 97)

RIP v2 remains unsuited for network environments that require routes to be selected in real - time based on either delay, traffic loads, or any other dynamic network performance metric. (page 98)

IS-IS is a very flexible protocol and has been extended to incorporate leading edge features such as Multiprotocol Label Switching Traffic Engineering (MPLS/TE). (page 101)

The IS-IS protocol is designed to operate in an OSI Connectionless Network Service (CLNS) environment. (page 102)

IS - IS selects routes based upon a __________ assigned to links in the IS - IS network. (page 102)

CLNP is the solution for “unreliable” (connectionless) delivery of data, similar to IP. (page 103)

IS - IS uses _______ addresses to identify the routers and to build the link - state database (LSDB). (page 103)

Integrated IS - IS supports IP routing as well as CLNS. (page 104)

CLNS addresses are required for configuring and troubleshooting IS - IS, even when it is used only for IP. (page 104)

What data-link environments does IS-IS support? (page 104)

IS - IS is comparable to, and in some cases preferable to, OSPF. (page 105)

What do OSPF and IS-IS have in common? (page 106)

The OSI protocol suite uses CLNS to provide connectionless delivery of data, and the actual Layer 3 protocol is the CLNP. (page 107)

IS - IS serves as an IGP for the CLNS. (page 107)

The original IS - IS implementation only supported ......... (page 107)

IS - IS allows the routing domain to be partitioned into areas. (page 108)

Level 1 routing occurs within an IS - IS area. (page 109)

With IS-IS, all devices in a Level 1 routing area have the same area address. (page 109)

Level 2 routers learn the locations of Level 1 routing areas and build an interarea routing table. (page 109)

All ISs in a Level 2 routing area use the destination area address to route traffic using the lowest cost path. (page 109)

IS-IS Level 1 routers..... (page 110)

IS-IS Level 2 routers..... (page 110)

IS-IS Level 1-2 routers.....

The path of connected Level 2 and Level 1 – 2 routers is called the backbone. (page 110)

In IS-IS, all areas and the backbone must be contiguous. (page 110)

In IS-IS, area boundaries fall on the links. (page 110)

Level 1 - 2 routers act as border routers between Level 1 and Level 2 routing domains. (page 111)

Integrated IS - IS provides IP with an alternative to OSPF and combines ISO CLNS and IP routing in one protocol. (page 112)

Integrated IS - IS uses its own protocol data units (PDUs) to transport information between routers, including IP reachability information. (page 112)

IS - IS information is not carried within a network - layer protocol; instead, it is carried directly within........... (page 112).

In a IS-IS network design, using areas confines the scope of LSP propagation and saves bandwidth. (page 114)

In a IS-IS network design, the logical place to implement route summarization is on the Level 1 – 2 routers, which is on the border between a Level 1 area and the Level 2 backbone. (page 114)

Hosts in the OSI terminology are called.............. (page 115)

The End System - to - Intermediate System (ES - IS) protocol permits Ess (hosts) and ISs (routers) to discover one another. (page 115)

ES - IS allows ESs to learn their network - layer addresses. (page 115)

ES - IS performs which following tasks? (page 115)

ESs listen for ISHs and randomly pick an IS to which they forward all their packets. (page 116)

When an ES needs to send a packet to another ES, it sends the packet to one of the ISs (routers) on its directly attached network. (page 116)

IP systems use ES - IS. (page 116)

IP has its own processes and applications to handle the same functions as ES - IS, such as Internet Control Message Protocol (ICMP). (page 116)

How many routing operations are there in OSI routing? (page 117)

OSI routing begins with ES - IS when the ESs discover the nearest IS by listening to ISH packets. This is done on..... (page 117)

When an ES needs to send a packet to another ES, it sends the packet to an IS on an attached network. This is done on.... (page 117)

Each ES and IS resides in a particular area. This is in..... (page 117)

To pass traffic, the router looks up the destination address and forwards the packet using the best route. This is done in..... (page 117)

If the destination is on the same subnetwork , the IS is aware of the location (from listening to the ESH) and forwards the packet appropriately. This is done in.... (page 117)

IS can provide a redirect message to the source that tells it that a more direct route is available. This is done in.... (page 117)

If the destination is on a different subnetwork but within the same area, the router identifies the best path using the system ID and forwards the traffic appropriately. This is done in.... (page 117)

If a destination address is in another area, the Level 1 IS sends the packet to the nearest Level 1 – 2 IS. This is done in... (page 118)

Packet forwarding continues through Level 2 ISs until the packet reaches a Level 1 – 2 or Level 2 IS in the destination area. (page 118)

Within the destination area, ISs forward the packet along the best path, based on system ID, until the packet reaches the destination. This is done in.... (page 118)

Routing between separate domains is called Level 3 routing. (page 118)

Level 3 routing is comparable to Border Gateway Protocol (BGP) interdomain routing in IP. (page 118)

Level 3 routing passes traffic between different autonomous systems, which might have different routing logic but might not have metrics that can be directly compared. (page 118)

Level 3 OSI routing is implemented on Cisco routers. (page 118)

With OSPF, network design is constrained by the fact that OSPF is based on a central backbone (area 0), with all other areas being physically attached to area 0. (page 119)

The border between areas is inside the ABRs and each link is only in one area. (page 119)

Summarization also reduces the amount of information carried in the backbone and advertised across the network. (page 119)

IS - IS permits a more flexible approach to extending the backbone by simply adding more Level 2 and Level 1 – 2 routers, which is a less complex process than with OSPF. (page 119)

OSPF runs on top of IP, whereas IS - IS runs through CLNS. (page 120)

OSPF produces many small LSAs. (page 120)

IS - IS updates are grouped by the router and sent as one LSP; therefore, the number of IS - IS updates is not an issue as network complexity increases. (page 120)

Since IS - IS uses significantly fewer LSPs, at least 1,000 routers can reside in a single area, making IS - IS more scalable than OSPF. (page 120)

Based on the default timers, IS - IS detects a failure faster than OSPF; therefore, convergence occurs more rapidly. (page 121)

IS - IS is also more efficient than OSPF in the use of CPU resources and in the way it processes routing updates. (page 121)

Similar to a designated router (DR) in OSPF, IS - IS elects a designated IS router (DIS). (page 122)

IS - IS does not elect a backup DR like OSPF does. (page 122)

IS - IS doesn't repeat the election process whenever a new router becomes active. (page 122)

A company may choose OSPF over IS - IS, because OSPF is more optimized and was designed exclusively as an IP routing protocol. (page 122)

The default OSPF metric is related to the interface bandwidth, while IS - IS defaults to a metric of 10 on all interfaces. (page 122)