CCC NET 126 Chapter 7
15
A RIPv1 hop count greater than _______ hops is deemed infinite (too far). That numbered hop router would not propagate the routing update to the next router.
autonomous system
A ________ is a collection of routers under a common administration such as a company or an organization.
metric
A ___________is a measurable value that is assigned by the routing protocol to different routes based on the usefulness of that route.
False
A difference between link state and distance vector protocols is that link state protocols use periodic updates to keep their routing tables converged.
ultimate
A level 1 parent route is a level 1 network route that is subnetted. A parent route can never be an __________________________ route.
Network route - A network route that has a subnet mask equal to that of the classful mask. Supernet route - A supernet route is a network address with a mask less than the classful mask, for example, a summary address. Default route - A default route is a static route with the address 0.0.0.0/0.
A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network address. List and explain three types of level 1 routes.
classful
A level 2 child route is a route that is a subnet of a _________________ network address.
True
A negative aspect of using dynamic routing protocols is dedicating part of a router's resources for protocol operation, including CPU time and network link bandwidth.
The route source was learned dynamically.
A network administrator has examined the routing table of a router and noted that the entry for the destination network 172.16.4.0/24 begins with the letter D. What does this letter signify?
False
A network is completely operable even though the network has not fully converged.
True
A primary benefit of dynamic routing protocols is that routers exchange routing information when there is a topology change.
link-state
A router configured with a_____________routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.
True
A routing protocol is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol's choice of best paths.
dynamic routing
Adapts to topology changes to reroute traffic, when possible
The next step is for the router to begin exchanging routing updates to learn about any remote routes.
After a router is first booted it learns about any directly connected networks. If a routing protocol is configured, what is the next step is for the router?
True
All link-state routing protocols apply Dijkstra's algorithm to calculate the best path route.
Each router learns about its own links and its own directly connected networks. This is done by detecting that an interface is in the up state. Each router is responsible for meeting its neighbors on directly connected networks. Link state routers do this by exchanging Hello packets with other link-state routers on directly connected networks. Each router builds a Link-State Packet (LSP) containing the state of each directly connected link. This is done by recording all the pertinent information about each neighbor, including neighbor ID, link type, and bandwidth. Each router floods the LSP to all neighbors. Those neighbors store all LSPs received in a database. They then flood the LSPs to their neighbors until all routers in the area have received the LSPs. Each router stores a copy of each LSP received from its neighbors in a local database. Each router uses the database to construct a complete map of the topology and computes the best path to each destination network. Like having a road map, the router now has a complete map of all destinations in the topology and the routes to reach them. The SPF algorithm is used to construct the map of the topology and to determine the best path to each network.
All routers in a topology will complete the same generic link-state routing process to reach a state of convergence. Explain each step.
True
All routing protocols are designed to learn about remote networks and to quickly adapt whenever there is a change in the topology.
Interior Gateway Routing Protocol - IGRP - and Enhanced IGRP - EIGRP
Cisco developed two protocols which also scale well in larger network implementations. These are:
A discontiguous network is when subnets from the same classful major network address are separated by a different classful network address.
Classful routing protocols create problems in discontiguous networks. Explain what a discontiguous network is.
False
Classfull routing protocols support VLSM and CIDR.
RIPv2, EIGRP, OSPF, and IS-IS
Classless IPv4 routing protocols all include the subnet mask information with the network address in routing updates. They also support VLSM and CIDR. List these IPv4 protocols.
False
Compared to static routing, dynamic routing protocols require more administrative overhead.
Convergence time is the time it takes routers to share information, calculate best paths, and update their routing tables.
Define convergence time.
IGRP
Distance Vector Routing Protocol
Split horizon prevents information from being sent out the same interface from which it was received.
Distance vector routing protocols typically implement a routing loop prevention technique known as split horizon. Explain.
BGP
EGP, path-vector, classless protocol
True
EIGRP introduced bounded triggered updates: It does not send periodic updates. Only routing table changes are propagated whenever a change occurs.
static routing
Easy to implement in a small network
The network design is hierarchical, usually occurring in large networks Fast convergence of the network is crucial The administrators have good knowledge of the implemented link-state routing protocol
Explain in what situations Link-state protocols work best.
The biggest distinction between classful and classless routing protocols is that classful routing protocols do not send subnet mask information in their routing updates. Classless routing protocols include subnet mask information in the routing updates.
Explain the biggest distinction between classful and classless routing protocols.
Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. Routing to and from a stub network, which is a network with only one default route out and no knowledge of any remote networks. Accessing a single default route (which is used to represent a path to any network that does not have a more specific match with another route in the routing table).
Explain the primary uses static routing has.
S - Identifies that the route was manually created by an administrator to reach a specific network. This is known as a static route. D - Identifies that the route was learned dynamically from another router using the EIGRP routing protocol. O - Identifies that the route was learned dynamically from another router using the OSPF routing protocol. R - Identifies that the route was learned dynamically from another router using the RIP routing protocol.
Explain what each of the following routing table codes indicate.
In contrast to distance vector routing protocol operation, a router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.
How is a router configured with a link-state routing protocol different from a router configured with a distance vector protocol?
RIP sends a periodic update to all of its neighbors every 30 seconds.
How often does RIP send out routing updates?
RIPv2
IGP, distance vector, classless protocol
EIGRP
IGP, distance vector, classless protocol developed by Cisco
OSPF
IGP, link-state, classless protocol
level 1 ultimate
IPv6 is classless by design, all routes are effectively _________________________________ routes. There is no level 1 parent of level 2 child routes.
Route timestamp
Identifies from when the route was last heard.
Distance
Identifies how far it is to the destination network and is based on a metric such as the hop count, cost, bandwidth, delay, and more.
Route source
Identifies how the route was learned.
Destination network
Identifies the address of the remote network.
Even though the router only sends RIPv1 messages, it can interpret both RIPv1 and RIPv2 messages. A RIPv1 router ignores the RIPv2 fields in the route entry.
If a router is running RIPv1 and it receives a RIPv2 message, how does it interpret the RIPv2 message.
It still has a 15 hop limitation and the administrative distance is 120.
In 1997, the IPv6 enabled version of RIP was released. RIPng is based on RIPv2. What is Its hop count and administrative distance?
The router sends and receives routing messages on its interfaces. The router shares routing messages and routing information with other routers that are using the same routing protocol. Routers exchange routing information to learn about remote networks. When a router detects a topology change the routing protocol can advertise this change to other routers.
In general, describe the operations of a dynamic routing protocol.
Topology table Neighbor table Best path(s) in the routing table
In the area of data structure, EIGRP creates and maintains what information?
Acknowledgements Queries Updates Replies Hellos
In the area of routing protocol messages, what does EIGRP use?
During initial startup of the routing protocol process on that router (e.g., router restart) Whenever there is a change in the topology (e.g., a link going down or coming up, a neighbor adjacency being established or broken)
LSPs do not need to be sent periodically. When do LSPs need to be sent?
IS-IS
Link State Routing Protocol
shortest path first
Link-state routing protocols are also known as _______________________________ protocols.
Classless routing protocol - It supports VLSM and CIDR, because it includes the subnet mask in the routing updates. Increased efficiency - It forwards updates to multicast address 224.0.0.9, instead of the broadcast address 255.255.255.255. Reduced routing entries - It supports manual route summarization on any interface. Secure - It supports an authentication mechanism to secure routing table updates between neighbors.
List and explain the improvements introduced in RIPv2.
Route source - Identifies how the route was learned. Directly connected interfaces have two route source codes (C identifies a directly connected network while L identifies that this is a local route.) Directly connected network - The IPv6 address of the directly connected network. Administrative distance - Identifies the trustworthiness of the route source. IPv6 uses the same distances as IPv4. A value of 0 indicates the best, most trustworthy source. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. Outgoing interface - Identifies the exit interface to use when forwarding packets to the destination network.
List and explain what information directly connected route entries display in a show IPv6 routing table.
Builds a Topological Map Fast Convergence Event-driven Updates Hierarchical Design
List the advantages of link-state routing protocols compared to distance vector routing protocols.
Bandwidth, delay, load, and reliability are used to create a composite metric. Routing updates are broadcast every 90 seconds, by default.
List the design characteristics the Interior Gateway Routing Protocol (IGRP) was developed with.
Bounded triggered updates, Hello keepalive mechanism, Maintains a topology table, Rapid convergence, Multiple network layer protocol support
List the differences introduced in EIGRP.
Memory Requirements Processing Requirements Bandwidth Requirements
List the disadvantages link-state protocols have compared to distance vector routing protocols?
OSPF - Popular standards based routing protocol IS-IS - Popular in provider networks
List two link-state IPv4 IGPs.
1. If a routing protocol is configured, the next step is for the router to begin exchanging routing updates to learn about any remote routes. 2. After initial boot up and discovery, the routing table is updated with all directly connected networks and the interfaces those networks reside on. 3. The router sends an update packet out all interfaces that are enabled on the router. The update contains the information in the routing table, which currently are all directly connected networks.
Match the number with the process to indicate the correct order a router performs the following steps in.
Examining level 1 network routes for the best match Examining child routes of the parent route for the best match Searching level 1 supernet routes for best match Determining if a default route exists Dropping the packet
Match the steps that are taken by a router in the route look up process when it receives a packet, there is no match, and the packet is eventually dropped.
Memory, CPU, and bandwidth
Modern link-state routing protocols are designed to minimize the effects on:
RIP v1
One of the first dynamic routing protocols was___________ which was released in 1988.
BGP
Path-Vector Routing Protocol
dynamic routing
Requires more CPU, RAM, and link bandwidth
static routing
Route to the destination is always the same
metrics
Routers use _________ to help determine the best path.
A neighbor is any other router that is enabled with the same link-state routing protocol.
Routers with link-state routing protocols use a Hello protocol to discover any neighbors on its links. What is a neighbor?
True
Routing protocols can also classified as whether it supports classless or classful IP addressing.
Purpose - Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP) Operation - Distance vector, link-state protocol, or path-vector protocol Behavior - Classful (legacy) or classless protocol
Routing protocols can be classified into three different groups according to their characteristics. List and explain each category.
Data structures
Routing protocols typically use tables or databases for its operations. This information is kept in RAM.
data structures
Routing protocols typically use tables or databases for their operations. This information is kept in RAM.
algorithm
Routing protocols use these for facilitating routing information and for best path determination.
routing protocol messages
Routing protocols use various methods of communication to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network.
Routing protocol messages
Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network.
Wasted Bandwidth - Bandwidth is used to transport unnecessary updates. Because RIP updates are either broadcasted or multicasted; therefore, switches also forward the updates out all ports. Wasted Resources - All devices on the LAN must process the update up to the transport layers, at which point the devices will discard the update. Security Risk - Advertising updates on a broadcast network is a security risk. RIP updates can be intercepted with packet sniffing software. Routing updates can be modified and sent back to the router, corrupting the routing table with false metrics that misdirect traffic.
Sending out unneeded updates on a LAN impacts the network in what ways?
Vector
Specifies the direction of the next-hop router or exit interface to reach the destination.
True
Split horizon prevents information from being sent out the same interface from which it was received.
dynamic routing
Suitable for multiple router topologies
Interior Gateway Protocols (IGP) - Used for routing within an AS. It is also referred to as intra-AS routing. Companies, organizations, and even service providers use an IGP on their internal networks. IGPs include RIP, EIGRP, OSPF, and IS-IS. Exterior Gateway Protocols (EGP) - Used for routing between AS. It is also referred to as inter-AS routing. Service providers and large companies may interconnect using an EGP. The Border Gateway Protocol (BGP) is the only currently-viable EGP and is the official routing protocol used by the Internet.
The Internet is based on the AS concept; therefore, two types of routing protocols are required:. List and explain both.
Always the preferred route.
The best match is the route in the routing table that has the most number of far left matching bits with the destination IPv4 address of the packet. What is the route with the greatest number of equivalent far left bits, or the longest match?
Discovery of remote networks Maintaining up-to-date routing information Choosing the best path to destination networks Ability to find a new best path if the current path is no longer available
The purpose of dynamic routing protocols includes:
The cost to reach a router indirectly may be less than the cost to reach it directly.
The shortest path between two routers is not necessarily the path with the least number of hops. What does this mean?
That RIPng routing is configured and running on router R1. The interfaces configured with RIPng.
The show ipv6 protocols command does not provide the same amount of information as its IPv4 counterpart. What does it confirm?
directly connected network, static route, or a dynamic routing protocol.
The source of the level 1 route can be a:
Scalability
This defines how large a network can become, based on the routing protocol that is deployed. The larger the network is, the more scalable the routing protocol needs to be.
Speed of convergence
This defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence, the more preferable the protocol. Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network.
Implementation and maintenance
This describes the level of knowledge that is required for a network administrator to implement and maintain the network based on the routing protocol deployed.
Algorithm
This is a finite list of steps used to accomplish a task. Routing protocols use these for facilitating routing information and for best path determination.
Open Shortest Path First - OSPF - and Intermediate System-to-Intermediate System - IS-IS
To address the needs of larger networks, two advanced routing protocols were developed. These are:
To enable an IPv6 router to forward IPv6 packets, the ipv6 unicast-routing must be configured.
To enable an IPv6 router to forward IPv6 packets, what command must be configured?
interface
Unlike RIPv2, RIPng is enabled on an ___________________ and not in router configuration mode.
passive-interface
Use the ________ router configuration command to prevent the transmission of routing updates through a router interface, but still allow that network to be advertised to other routers.
DUAL
What algorithm does EIGRP use to identify the best route to a network?
RIPv1 - First generation legacy protocol RIPv2 - Simple distance vector routing protocol IGRP - First generation Cisco proprietary protocol (obsolete and replaced by EIGRP) EIGRP - Advanced version of distance vector routing
What are four distance vector IPv4 interior gateway protocols?
Routing protocols are used to facilitate the exchange of routing information between routers.
What are routing protocols are used to facilitate?
Dynamic routing protocols work well in any type of network consisting of several routers. They are scalable and automatically determine better routes if there is a change in the topology. Although there is more to the configuration of dynamic routing protocols, they are simpler to configure in a large network.
What are the advantages of using dynamic routing protocols?
Dynamic routing requires knowledge of additional commands. It is also less secure than static routing because the interfaces identified by the routing protocol send routing updates out. Routes taken may differ between packets. The routing algorithm uses additional CPU, RAM, and link bandwidth.
What are the disadvantages of using dynamic routing protocols?
They are not easy to implement in a large network. Managing the static configurations can become time consuming. If a link fails, a static route cannot reroute traffic.
What are the disadvantages of using static routing?
Routing updates are broadcasted (255.255.255.255) every 30 seconds. The hop count is used as the metric for path selection. A hop count greater than 15 hops is deemed infinite (too far). That 15th hop router would not propagate the routing update to the next router.
What are the key characteristics of RIPv1?
Open Shortest Path First (OSPF) Intermediate System-to-Intermediate System (IS-IS)
What are the two IPv4 link-state routing protocols?
They compute their own knowledge of the network topology. They require a lot of hardware resources.
What are two characteristics of link-state protocols compared to distance vector protocols?
to discover the network to maintain routing tables
What are two functions of dynamic routing protocols?
Speed of Convergence, Scalability, Classful or Classless (Use of VLSM), Resource Usage
What characteristics can routing protocols be compared on?
version 2
What command is required after the router rip command is issued to force a router to run RIPv2?
network 192.168.1.0
What command is used to enable RIP routing for the 192.168.1.0 network?
To enable RIP, use the router rip command
What command is used to set up RIP on a router?
The network has converged when all routers have complete and accurate information about the entire network.
What does it mean when a network is converged?
The show ip protocols command displays the IPv4 routing protocol settings currently configured on the router.
What does the show ip protocols command display?
The show ip route command displays the RIP routes installed in the routing table.
What does the show ip route command display?
The show ipv6 route command displays the routes installed in the routing table
What does the show ipv6 route command display?
If a router stops receiving Hello packets from a neighbor, that neighbor is considered unreachable and the adjacency is broken.
What happens if a router stops receiving Hello packets from a neighbor?
When automatic summarization has been disabled, RIPv2 no longer summarizes networks to their classful address at boundary routers. RIPv2 now includes all subnets and their appropriate masks in its routing updates.
What happens on a router running RIPv2 if automatic summarization is disabled?
Route source Destination network Outgoing interface
What information do automatically configured routing table entries contain?
A primary benefit of dynamic routing protocols is that routers exchange routing information when there is a topology change. This exchange allows routers to automatically learn about new networks and also to find alternate paths when there is a link failure to a current network.
What is a primary benefit of dynamic routing protocols?
fast convergence
What is an advantage of OSPF compared to RIP?
An autonomous system - AS - is a collection of routers under a common administration such as a company or an organization. An AS is also known as a routing domain. Typical examples of an AS are a company's internal network and an ISP's network.
What is an autonomous system (AS)?
Interior routing protocols are used to communicate within a single autonomous system. Exterior routing protocols are used to communicate between multiple autonomous systems.
What is the difference between interior and exterior routing protocols?
In situations where there are multiple paths to the same remote network, the routing metrics are used to determine the overall "cost" of a path from source to destination.
What is the purpose of a routing metric?
to explain the operation of the hierarchical structure of the routing table
What is the purpose of classifying Cisco IP routing table entries as ultimate route, level 1 route, level 1 parent route, and level 2 child routes?
The Border Gateway Protocol (BGP) is now used between Internet service providers (ISPs). BGP is also used between ISPs and their larger private clients to exchange routing information.
What protocol was developed to connect different internetworks and provide routing between them, and connect ISPs and their larger private clients to exchange routing information?
Use the passive-interface router configuration command to prevent the transmission of routing updates through a router interface, but still allow that network to be advertised to other routers.
What router configuration command can be used to prevent the transmission of routing updates through a router interface, but still allow that network to be advertised to other routers?
One of the first routing protocols was Routing Information Protocol - RIP
What was one of the first routing protocols used?
True
When a router powers up, it knows nothing about the network topology.
Dijkstra's algorithm
Which algorithm is used by the OSPF routing process to construct the SPF tree on a router?
EIGRP
Which classless routing protocol supports VLSM and CIDR, bounded and triggered updates, and uses the multicast address of 224.0.0.10?
RIPv2
Which classless routing protocol supports VLSM and CIDR, supports manual route summarization, and uses the multicast address 224.0.0.9?
size of the network
Which factor directly affects the time to convergence?
only uses classful IPV4 addressing
Which of the following is not a distance vector routing characteristic?
discovery of local networks
Which of the following is not a purpose of a dynamic routing protocol?
All routing protocols support the passive-interface command.
Which routing protocols support the passive-interface command?
They are used to maintain neighbor relationships. They are used for dynamic neighbor discovery.
Which two statements are true for OSPF Hello packets?
All IPv6 routing protocols are considered classless because they include the prefix-length with the IPv6 address.
Why are all IPv6 routing protocols are considered classless?
Networks with moderate levels of complexity may have both static and dynamic routing configured.
Will a network with moderate levels of complexity have static routing, dynamic routing, or both configured?
Converging
__________ time is the time it takes routers to share information, calculate best paths, and update their routing tables.
