3C Flashcards
As discussed earlier, routing involves two basic activities: determination of optimal routing paths (____ ____) and the transport of packets through an internetwork (___ ___).
Path Determination
Packet Switching
Routers use routing tables to determine the best path. Routers populate their routing tables by learning paths to network destinations. The paths can be learned from ____ routes, ____ routes or ____ routes.
static, default or dynamic
Routers chose the path with the lowest ____ ____ (AD) when they know about multiple paths to the same destination from more than one routing source.
Administrative Distance (AD)
Static routes are manually configured by the system administrator as the ____ path to the destination.
only
Static routes are useful for controlling what?
They are useful for controlling security and reducing traffic.
Static routes are basically nothing more than ____ ____ entries established by the network administrator prior to the beginning of routing.
router table
____ ____ entries do not change unless the network administrator alters them.
Static route
Static routes are simple to configure and work well in environments where network traffic is relatively predictable and where network design is relatively simple. However, because static routing systems cannot react to network changes, they generally are considered ____ for today’s large, diverse networks.
unsuitable
Routers know about networks that are directly connected to them if their _____ are functional.
interfaces
When configuring static routes, look for paths that are not directly connected to the router that you want to be part of a path from source to destination. These routes are added to the routing table as ____ ____ reachable.
network destinations
A ___ ____ is a special static route manually defined by the system administrator as the path to take when no route to the destination is known.
default route
A default route, often called the ____ ____ ____ _____,
is a route to which all non-routable packets are sent.
gateway of last resort
___-____ is defined as a network that is not listed in a router’s routing table.
Non-routable
A ____ ____ is a Network Layer protocol that exchanges information packets with other internetwork routers to build and maintain a routing table.
routing protocol
Most of the dominant routing algorithms used today are dynamic routing algorithms such as…?
such as RIP, IGRP, OSPF, EIGRP, and BGP.
What metrics are involved in routing algorithms?
- Path Length
- Reliability
- Delay
- Bandwidth
- Load
- Communication cost
___ ____ is the most common routing metric used in routing algorithms.
Path length
The following describes which routing metric?
Some routing protocols allow network administrators to assign arbitrary costs to each network link. In this case, ___ ____ is the sum of the costs associated with each link traversed. Other routing protocols define hop count as a metric that specifies the number of passes (hops) through internetworking devices, such as routers, that a packet must take from a source to a destination.
path length
The following describes which routing metric?
In the context of routing algorithms, refers to the dependability (usually described in terms of the bit-error rate) of each network link. Some network links might go down more often than others. After a network fails, certain network links might be repaired more easily or more quickly than other links. Any reliability factors can be considered in the assignment of a reliability rating. These are arbitrary numeric values usually assigned to network links by network administrators
Reliability
The following describes which routing metric?
refers to the length of time required to move a packet from source to destination through the internetwork. ____ depends on many factors, including the bandwidth of intermediate network links, the port queues (information waiting to be processed) at each router along the way, network congestion on all intermediate network links, and the physical distance to be traveled. Because ____ is a conglomeration of several important variables, it is a common and useful metric.
Delay
The following describes which routing metric?
refers to the available traffic capacity of a link. All other things being equal, a 10Mbps Ethernet link would be preferable to a 64kbps leased line. Although ____ is a rating of the maximum attainable throughput on a link, routes through links with greater ____ do not necessarily provide better routes than routes through slower links. For example, if a faster link is busier, the actual time required to send a packet to the destination could be greater.
Bandwidth
The following describes which routing metric?
refers to the degree to which a network resource, such as a router, is busy. _____ can be calculated in a variety of ways, including CPU utilization and packets processed per second. Monitoring these parameters on a continual basis can be resource intensive.
Load
The following describes which routing metric?
Is another important metric especially because some organizations may not care about performance as much as they care about operating expenses. Even though line delay may be longer, they will send packets over their own lines rather than through the public lines that cost money for usage time. This metric, when used, is set by the Network Administrator.
Communication cost
Algorithms can be classified in several ways; however, we will focus on the two primary types of ____ ____ and ____ ____ algorithms
Distance Vector and Link State algorithms
____ ____ initialize and maintain routing tables, which contain
route information that can vary depending on the routing algorithm used.
Routing Algorithms
____ ____ algorithms use an approach that determines the direction (vector) and distance to any link in the internetwork.
Distance Vector
The network topology changes and at regular intervals. ____ ____ algorithms call for each router to send its entire routing table, but only to its neighbors by way of limited broadcasts.
Distance Vector algorithms
The routing updates do not include subnet masks for the advertised networks. This means all routers in the network must use the same subnet mask. This is known as ____ routing.
classful routing
When a router receives a routing update that includes changes to an entry, it updates its routing table to reflect the new route. After updating its routing table, the router immediately begins transmitting routing updates to inform its neighbor routers of the change. These updates are sent independently of any regularly scheduled updates. This form of routing update is often called “___ ___ ___” since the routers don’t know where the information initially came from and must assume the information is correct
routing by rumor
What are the advantages of distance vector algorithms?
- Simple to understand and configure.
- Do not require much from the router’s processor to maintain the routing table.
- Less expensive to implement and support.
What are the disadvantages of distance vector algorithms?
- Limited by hop count thereby making them unsuitable for large networks
- Variable length subnet masking not supported in RIPv1.
- Update by broadcast and build their routing tables from their neighbor’s routing tables. This means they are routing based on information that cannot be verified as accurate
Link State algorithms are also known as what name?
Shortest path first algorithms
____ _____ algorithms build a complete topological map of the entire area in memory, which allows them to “see” the entire path to the destination network ensuring the path is valid and is the best path available.
Link State algorithms
Link state algorithms use ____ ____ state advertisements to notify other routers in the routing area about the status of their connected links.
multicast link state advertisements
The following is describing which of the algorithms?
When routers receive the message, they copy the information for their own use and immediately resend the message through their other interfaces. This allows for very fast convergence of new information.
Link State algorithms
Benefits provided by ___ ___ algorithms are support for variable length subnet masks (VLSM) and each router sending information describing the state of its own links.
Link State algorithms
Basically, link state algorithms send small updates everywhere, while distance vector algorithms send larger updates but only to their ___ ____.
neighboring routers
Because they converge more quickly, link state algorithms are less prone to ____ ____ than distance vector algorithms.
routing loops
On the other hand, link state algorithms require more ___ _____ and
______ than distance vector algorithms. Link state algorithms, therefore, can be more expensive to implement and support.
CPU power and memory
Interior routing protocols are used to exchange information between routers within ____ ____.
Autonomous Systems
We will look at the most common interior gateway routing protocols which are based on either a distance vector algorithm (___), a link state algorithm (OSPF), or a balanced hybrid of the two algorithm types. (EIGRP)
(RIP)
Routing Information Protocol or RIP, as it is more commonly called, utilizes a ____ ____ algorithm.
Distance Vector algorithm
RIPs metric is hop count, limited to ___.
15
When communicating with other routers, RIP sends broadcast routing update messages every ___ seconds and when the network topology changes.
30 seconds
These changes are then updated in the router’s routing table. RIP routers maintain only the best route (the route with the ____ _____ ____) to a destination.
lowest metric value
After updating its routing table, the router immediately begins transmitting routing updates to inform other network routers of the change. These updates are sent independently of the regularly scheduled updates that RIP routers send. One important thing to note is that these updates are sent only to a router’s ___ ___ ___ and updated one router at a time resulting in longer convergence times. The broadcast message cannot travel beyond the directly connected neighbor routers since the broadcast message is stopped by the first router interface it encounters.
directly connected neighbors
Another drawback to RIP is that it does not support ____ ____ subnet masking as it does not include subnet mask information in the routing updates.
variable length
_____ improves on RIP by allowing the use of variable length subnet masking as it includes subnet mask data in all routing updates. Another improvement is the use of multicast messages to send routing updates which speeds up convergence time.
RIPv2
RIPng was developed for _____.
IPv6
What does OSPF stand for?
Open Shortest Path First
What algorithm does RIP use?
Distance vector algorithm
What algorithm does OSPF use?
link state algorithm
OSPF was created in the late 1980s as a solution to RIP’s inability to handle…?
routing in large, diverse networks
OSPF is a link state routing protocol that only sends information which describes the state of its own links to all the routers within the same…?
hiearchial area
Interface information, metrics used, and other variables are included in OSPF’s ___ ___ ____ (LSAs).
Link State Advertisements
OSPF routers use Dijkstra’s ____ ____ ____ (SPF) algorithm to calculate the shortest path to each router.
Shortest Path First
OSPFs metric is cost based on a ___ Mbps reference bandwidth divided by the interface bandwidth.
100
OSPF operates best within a hierarchy. The largest entity within the hierarchy is the __, which is a collection of networks under a common administration that share a common routing strategy.
AS
An AS is also called a ____ ____.
routing domain
An AS can be divided into several areas, which are groups of
____ ____ and ____ ____.
contiguous networks
attached hosts
Routers with multiple interfaces can participate in multiple areas. These routers are called ____ _____ routers and maintain separate topological databases for each area.
area border
When running a multi-area OSPF network, a ___ ___ scheme is required.
hierarchical address
Multi-area OSPF should be built within a hierarchical structure, unlike ___.
RIP
IP subnet masks are included with each advertised destination, enabling variable-length subnet masks. This is ____ routing.
classless
OSPFv2 and OSPFv3 provide improvements with ____ supporting IPv6
OSPFv3
An OSPF backbone (commonly ____ _) is responsible for distributing routing information between areas.
Area 0
The OSPF backbone consists of all area border routers, networks not wholly contained in any area and their ___ ___.
attached routers
The backbone itself is an ___ ___ and, all backbone routers use the same procedures and algorithms as the other area routers to maintain routing information within the backbone.
OSPF area
The backbone topology is ____ to all intra-area routers, as are individual area topologies to the backbone.
invisible
The following is describing what OSPF routing strategy?
After a router is powered up and assured that its interfaces are functioning, it uses the OSPF Hello protocol to acquire neighbors, which are routers with interfaces to a common network. The router
sends hello packets to its neighbors and receives their hello packets. In addition to helping acquire neighbors, hello packets also act as a keep-alive to let routers know that their neighbor router and the link between them are still functional.
Initialization
The following describes what OSPF routing stategy?
When a router discovers a new neighbor, it records the neighbor’s address and interface as an entry in the neighbor table.
Neighbor table
The following describes what OSPF routing stategy?
The topology table is an overall picture of active router interfaces participating in OSPF. The topology table contains the collection of LSAs received from all routers in the same area. Because routers within the same area share the same information, they have identical topology tables. An area’s topology is invisible to routers outside the area. By keeping area topologies separate, OSPF passes less routing traffic than it would if the AS were not partitioned. All area routers share the same
topology table and the same networks listed in their routing tables
Topology Table
The following describes what OSPF routing stategy?
The SPF routing algorithm is the basis for OSPF operations. This algorithm uses the information from the topology table to calculate entries for insertion into the routing table.
SPF algorithm
The following describes what OSPF routing strategy?
From the topology table generated from LSAs, each router calculates a shortest-path tree, with itself as the root for each known sub-network. The shortest-path tree, in turn, yields entries into the routing table
Routing Table
What are the advantages of OSPF?
- Hierarchical routing supports very large networks.
- Shortest Path First algorithm allows for fast convergence.
- Does not suffer from the routing loop issues (unlike distant vector protocols).
- Supports classless routing (VLSM reduces routing protocol overhead).
- Smaller routing updates and, they only occur when there is a topology change (less bandwidth and CPU utilization).
What are the disadvantages of OSPF?
- Complex. Requires a structured topology (otherwise efficiency will be reduced).
- Requires highly trained staff to understand and configure a large OSPF network due to complex configurations.
- Link State database requires considerable memory due to numerous tables and databases.
- SPF algorithm utilizes more processing power as the size of the topology database increases
We have previously looked at the two primary classes of Routing Protocols. Both of these types of protocols have their advantages and disadvantages. ___ ___ are not well suited for large networks, utilize too much of the network bandwidth and ___ ____ ____ were too complicated and often required additional investments in equipment and expensive additional training for network managers.
Distance Vectors
Link State Protocols
What does EIGRP stand for?
Enhanced Interior Gateway Routing Protocol
Cisco developed EIGRP to overcome the limitations of IGRP on large networks caused by ___ ___ limitations.
hop count
EIGRPs default metrics are ____ and ____ but, reliability, load, and MTU
(Maximum Transmission Unit) may also be used.
bandwidth and delay
EIGRP was created as a ____ proprietary protocol. It was converted to open standard in 2013.
Cisco
EIGRP is often referred to as a “____ ____” because it combines the advantages of link-state protocols with those of distance vector protocols.
balanced hybrid
The following describes which routing protocol?
It maintains copies of its neighbor’s routing tables and uses these distance vectors to determine the best paths to destination networks but resembles link state protocols in the way it uses topology changes only to trigger link state updates by using multicast messages. EIGRP does not make periodic updates; instead, it sends link state updates only when there is a topology change
EIGRP
The name of the algorithm used by EIGRP is ____ ____ ____ (DUAL) Finite State Machine (FSM).
Diffusing Update Algorithm
Much like OSPF, EIGRP maintains multiple tables to assist with its routing decisions. EIGRP-enabled routers will maintain a separate ____ table, ____ table, and ___ table for each protocol supported.
neighbor table, topology table and routing table
The following describes what EIGRP table to assist with its routing decisions?
When a router discovers a new neighbor, it records the neighbor’s address and interface as an entry in the ___ ___.
Neighbor Table
The following describes what EIGRP table to assist with its routing decisions?
Remember, the overall goal of a router is to build a routing table no matter what method(s) are used for computations. In EIGRP, the best paths (successors) to each known network are extracted from
the topology table to build the routing table as computed by the DUAL FSM.
Routing Table
The following describes what EIGRP table to assist with its routing decisions?
The ____ ____ contains all destinations advertised by neighboring routers. A router using EIGRP will only advertise a route if it is being used to forward packets (the best route to the destination network even though the ____ ____ may contain other paths to the destination network.). Each entry in the ____ ____ includes the destination address and a list of neighbors that have advertised the destination. For each neighbor, the entry records the advertised metric. Each protocol enabled will populate its own table, and the table is acted on by the DUAL FSM to determine the best route (successor) and backup route (feasible successor)
Topology Table
What are the advantages of EIGRP?
- Fast convergence when a feasible successor is available.
- Variable Length Subnet Masks are supported - subnet mask information is exchanged in EIGRP updates.
- Smaller routing updates only sent when a topology change occurs.
- EIGRP scales to large networks.
What are the disadvantages of EIGRP?
- Higher memory requirements for its tables (neighbor, topology, and routing).
- Routing Algorithm is complex and can be CPU-intensive during periods of network
instability and recalculations. - No area concept.
When communications are required between autonomous systems, a different type of routing protocol is used. This type is called an ___ ___ ___ (EGP).
Exterior Gateway Protocol
EGPs are used to route information ____ autonomous systems.
between
What does BGP stand for?
Border Gateway Protocol
BGP is the predominant ____ in use today.
EGP
It is the protocol that runs the Internet.
BGP
Exterior routing algorithms are more _____ than interior routing algorithms because they must learn and track a greater number of
routers and routes.
complex
The primary function of ____ is to exchange routing information between autonomous systems while guaranteeing loop-free path selection
BGP
BGP is the protocol used between ___ ___ ___ (ISP) on the Internet.
Internet Service Providers
As of June 2019, the Internet BGP routing tables number more than ________ routes and growing.
780,000
BGP is considered a ____ ____ protocol.
path vector
BGP is capable of detecting routing loops and uses many route parameters, called ____ or ____ ____, to define routing policies and maintain a stable routing environment. For this reason, it guarantees loop-free path selection.
attributes or path vectors
Unlike Interior Routing Protocols, BGP ___ ___ ___ metrics such as hop count, bandwidth, or delay. Instead, BGP makes routing decisions based on network policies that are manually input by the
network administrators.
does not use
Unlike Interior Gateway Protocols, BGP does not contain any mechanism for automatic neighbor discovery. The network administrator must ____ define BGP neighbors (during configurations) and initiate a TCP connection-oriented session between the neighbor routers.
manually
BGP messaging is considered reliable because it uses ___ for acknowledgments between neighboring routers.
TCP
Small, standardized networks can get away with a ___ ____ to describe the best path to a destination, for example RIP uses hop count to choose the “shortest” path. Given the complexity of inter-AS routing, no single metric can describe the best path across various Autonomous Systems running multiple IGPs on diverse media.
single metric
The BGP route selection algorithm uses the ___ ___ to select a single
best path to each known destination.
attribute list
