Routing Protocols Flashcards
(163 cards)
1
Q
What is unicast communication?
A
Communication between one sender and one receiver, a one-to-one communication.
2
Q
What do routers create to support unicast communication?
A
Routing tables.
3
Q
What is an internet?
A
A combination of networks connected by routers.
4
Q
What decision do routers make when they receive a packet?
A
Which network to pass the packet to, based on optimization.
5
Q
What is cost or metric in routing?
A
A value assigned for passing through a network, used to minimize delay.
6
Q
What are the two types of routing tables?
A
Static and dynamic.
7
Q
What is a static routing table?
A
A routing table with manual entries.
8
Q
What is a dynamic routing table?
A
A routing table that is updated automatically when there is a change.
9
Q
What is a routing protocol?
A
A combination of rules and procedures that lets routers inform each other of changes.
10
Q
What is an autonomous system (AS)?
A
A group of networks and routers under the authority of a single administration.
11
Q
What is intra-domain routing?
A
Routing inside an autonomous system.
12
Q
What is inter-domain routing?
A
Routing between autonomous systems.
13
Q
Name one intra-domain routing protocol.
A
Routing Information Protocol (RIP).
14
Q
Name another intra-domain routing protocol.
A
Open Shortest Path First (OSPF).
15
Q
What is the implementation of path vector routing?
A
Border Gateway Protocol (BGP).
16
Q
What algorithm is used to find the shortest path in a graph?
A
Bellman-Ford algorithm.
17
Q
What does the Bellman-Ford algorithm do?
A
Finds the least cost (shortest path) between any two nodes.
18
Q
In distance vector routing, how is cost typically measured?
A
Hop counts.
19
Q
What must each router keep for each route?
A
Destination network, the cost, and the next hop.
20
Q
What is referred to as ‘R’ in the context of distance vector routing?
A
Record, which contains R.dest and R.cost.
21
Q
What happens when a router receives a record?
A
It searches for the destination address in the routing table.
22
Q
What should a router do if the record cost plus 1 is smaller than the table cost?
A
Update the route information to reflect a better route.
23
Q
What should a router do if an entry is not found in the table?
A
Add it to the table and sort according to the destination address.
24
Q
What is the default cost between any two neighbors in distance vector routing?
A
1.
25
What does each router create when it is booted?
Its own routing table
26
What is the problem referred to when a link is broken in distance vector routing?
Count to infinity
27
In distance vector routing, how quickly does an increase in cost propagate compared to a decrease?
Slowly for increase, quickly for decrease
28
What is defined as infinity in the context of RIP?
16
29
What is the maximum number of hops allowed in RIP?
15
30
What strategy involves sending only part of the routing table through each interface?
Split horizon
31
What does the poison reverse strategy do in routing?
Advertises a route with a metric of infinity if the source is the same node
32
What type of routing protocol is RIP classified as?
Intra-domain (interior) routing protocol
33
What metric does RIP use to define distance?
Hop count
34
What are the two types of messages in RIP?
Request and response
35
What is the purpose of the periodic timer in RIP?
Controls the sending of messages
36
What does the expiration timer in RIP govern?
The validity of a route
37
What happens if a router does not receive an update for a route within 180 seconds?
The route is considered expired and the hop count is set to 16
38
Fill in the blank: The metric used by RIP is called a _______.
Hop count
39
What does an unsolicited response in RIP indicate?
Sent periodically or when there is a change in the routing table
40
What is a two-node loop problem in routing?
Packets bounce between two nodes creating a loop
41
How does split horizon help in routing?
It prevents routing loops by limiting the information shared
42
What is the definition of a request message in RIP?
Sent by a router that has just come up or has time-out entries
43
What is the purpose of the garbage collection timer in RIP?
Advertises the failure of a route
44
True or False: The split horizon strategy can be combined with poison reverse.
True
45
What is the main drawback of the split horizon strategy?
It can lead to outdated information being kept in routing tables
46
What is the function of the distance field in a RIP message?
Defines the hop count from the advertising router to the destination network
47
What is the hop count set to?
16
48
What happens when the information about a route becomes invalid?
The router continues to advertise the route with a metric value of 16
49
What is the garbage collection timer set to for an invalid route?
120 s
50
When does a route get purged from the routing table?
When the garbage collection timer count reaches zero
51
How many timers are running if a routing table has 20 entries and does not receive information about five routes for 200 s?
21 timers
52
How many expiration timers are there in this scenario?
15
53
What is the significance of the route tag in RIP version 2?
Carries information such as the autonomous system number
54
What does the subnet mask field in RIP version 2 indicate?
Carries the subnet mask or prefix
55
What type of addressing does RIPv2 support?
Classless addressing and CIDR
56
What is the first entry in the RIP version 2 message format used for?
Authentication information
57
What multicast address does RIP version 2 use?
All-router multicast address
58
What is the assigned well-known port for RIP in UDP?
Port 520
59
What does each node in link state routing maintain?
The entire topology of the domain
60
Which algorithm is used to build a routing table in link state routing?
Dijkstra algorithm
61
What are the four sets of actions in link state routing?
["Creation of states of the links by each node", "Dissemination of LSPs to every other router", "Formation of a shortest path tree for each node", "Calculation of a routing table based on the shortest path tree"]
62
What minimum data does a link state packet (LSP) carry?
["Node identity", "List of links", "Sequence number", "Age"]
63
When are link state packets (LSPs) generated?
When there is a change in the topology or on a periodic basis
64
What is the purpose of flooding in link state routing?
To disseminate LSPs to all other nodes
65
What is a shortest path tree?
A tree where the path between the root and every other node is the shortest
66
What is the initial step in the Dijkstra algorithm?
Select the node as the root of the tree and add it to the path
67
What does OSPF stand for?
Open Shortest Path First
68
What type of routing protocol is OSPF?
Intra-domain routing protocol based on link state routing
69
What is an area in the context of OSPF?
A collection of networks, hosts, and routers within an autonomous system
70
What do area border routers do?
Summarize information about the area and send it to other areas
71
What is the backbone in OSPF?
A special area inside an autonomous system that connects all other areas
72
What can a backbone router also serve as?
An area border router
73
What is the primary area in an autonomous system?
Backbone
## Footnote
All other areas inside an autonomous system must be connected to the backbone, which serves as the primary area.
74
What are routers inside the backbone called?
Backbone routers
## Footnote
A backbone router can also be an area border router.
75
What must be created if connectivity between a backbone and an area is broken?
Virtual link
## Footnote
This virtual link must be created by the administration between routers.
76
What is the area identification of the backbone?
Zero
77
What does OSPF allow the administrator to assign to each route?
Cost (metric)
## Footnote
Metric can be based on a type of service such as minimum delay or maximum throughput.
78
In OSPF terminology, what is a connection called?
Link
79
What are the four types of links defined in OSPF?
* Point-to-point link
* Transient link
* Stub link
* Virtual link
80
What is a point-to-point link?
Connects two routers without any other host or router in between
81
What is a transient link?
Network with several routers attached to it
82
What is a stub link?
A network that is connected to only one router
83
What happens when the link between two routers is broken?
A virtual link can be created using a longer path
84
What is the most important packet type used by OSPF?
Link state update
85
What defines the version of the OSPF protocol?
Version field
86
What does the message length field define in OSPF packets?
Length of the total message including the header
87
What is the purpose of the checksum in OSPF packets?
Error detection on the entire packet excluding the authentication type and authentication data field
88
What indicates the number of seconds elapsed since a link state message was generated?
Link state age
89
What does the E flag indicate in OSPF?
The area is a stub area
90
What type of information does a router link LSA advertise?
Information about all of its links and neighbors
91
What does the link ID in a router link LSA depend on?
The type of link
92
What defines the metric for the default type of service in a router link LSA?
Metric for TOS 0
93
What does a network link LSA define?
The links of a network
94
What field in a network link LSA defines the network mask?
Network mask field
95
What IP addresses are defined in the attached router field of a network link LSA?
IP addresses of all attached routers
96
What is the purpose of LSAs in OSPF?
To advertise network links and routing information.
97
Which router advertises network link N1?
R1.
98
Which routers can advertise network link N2?
R1, R2, or R3.
99
Which router advertises network link N3?
R3.
100
What is the role of an area border router?
To announce the existence of networks outside the area.
101
How many routing tables does router R1 have?
Two.
102
What information does R1 flood area 1 with?
Information about how to reach a network located in area 0.
103
What fields are included in the summary link to network LSA?
* Network mask
* TOS
* Metric
104
What does the summary link to AS boundary router LSA provide?
Information about the route to an AS boundary router.
105
What is the format of the external link LSA similar to?
The summary link to the AS boundary router LSA.
106
What is the purpose of the Hello Message in OSPF?
To create neighborhood relationships and test reachability.
107
What does the priority field in the Hello packet determine?
The selection of the designated router.
108
What does the Dead interval field in the Hello packet signify?
The number of seconds before assuming a neighbor is dead.
109
What does the Database Description Message contain?
An outline of the database, not complete information.
110
What is the E flag in the Database Description Message?
Set to 1 if the advertising router is an autonomous boundary router.
111
What is the purpose of the Link State Request Packet?
To request information about specific routes.
112
What does the Link State Acknowledgment Packet do?
Acknowledges receipt of a packet.
113
How many different types of packets does OSPF use?
Five.
114
What is path vector routing used for?
Exterior routing for interdomain routing.
115
What instability issue is associated with distance vector routing?
Subject to instability if there are more than a few hops.
116
What does a router maintain in path vector routing?
A list of networks that can be reached with the path to each one.
117
Fill in the blank: The summary link to network LSA defines the _______.
network mask.
118
True or False: Each advertisement in OSPF can announce multiple networks.
False.
119
What does a router maintain to reach networks?
A list of networks that can be reached with the path to reach each one.
120
What must each Autonomous System (AS) have to provide information to other ASs?
At least one path vector routing that collects reachability information about each network in that AS.
121
What is a path vector routing table?
A table created for each router if ASs share their reachability list with each other.
122
What does a router R1 know about network 201.2.2.0/24?
It is in AS1.
123
What happens if a packet arrives for network 130.14.0.0/16?
The packet should travel from AS1 to AS2 to reach its destination.
124
What does path vector routing support?
CIDR notation and the aggregation of addresses.
125
Fill in the blank: Policy routing can be implemented through _______.
[path vector routing]
126
What is Border Gateway Protocol (BGP)?
An interdomain routing protocol using path vector routing.
127
When did BGP first appear?
1989.
128
What are the three categories of Autonomous Systems (ASs)?
* Stub
* Multihomed
* Transit
129
Describe a stub AS.
Has only one connection to another AS and cannot pass data traffic through.
130
What characterizes a multihomed AS?
Has more than one connection to other ASs but still only acts as a source or sink for data traffic.
131
What is a transit AS?
A multihomed AS that also allows transient traffic.
132
What type of addresses does BGP use?
Classless interdomain routing addresses.
133
What are path attributes in BGP?
Attributes that provide information about the path, divided into well-known and optional categories.
134
True or False: A well-known attribute must be recognized by every BGP router.
True.
135
What is a well-known mandatory attribute?
An attribute that must appear in the description of a route.
136
What is the purpose of the ORIGIN attribute?
Defines the source of the routing information.
137
What does the AS_PATH attribute define?
The list of autonomous systems through which the destination can be reached.
138
What does the NEXT-HOP attribute specify?
The next router to which the data packet should be sent.
139
What are the two categories of optional attributes?
* Transitive
* Nontransitive
140
What is an E-BGP session?
Used to exchange information between two speaker nodes belonging to different autonomous systems.
141
What is an I-BGP session?
Used to exchange routing information between two routers inside an autonomous system.
142
What is the function of a BGP session?
To exchange routing information between two routers.
143
What are the four types of BGP messages?
* Open
* Update
* Keepalive
* Notification
144
What does the Marker field in a BGP packet header do?
Reserved for authentication.
145
What does the Length field in a BGP packet header define?
The length of the total message including the header.
146
What is the purpose of the Open message in BGP?
To create a neighborhood relationship between routers.
147
What happens if a neighbor accepts a neighborhood relationship in BGP?
It responds with a keepalive message.
148
What is the Hold time in the Open message?
The maximum number of seconds until one party receives a keepalive or update message.
149
What is the purpose of the Update message in BGP?
To withdraw destinations, announce a route to a new destination, or both.
150
What does the Network layer reachability information (NLRI) define?
The network that is actually advertised by the Update message.
151
What defines the length of the next field in a BGP message?
A 2-byte field defines the length of the next field
152
What do path attributes define in a BGP message?
The attributes of the path (route) to the network being announced
153
What does the Network Layer Reachability Information (NLRI) define?
The network that is actually advertised by the message
154
What is included in the NLRI?
A length field and an IP address prefix
155
In the IP address prefix 153.18.7.0/24, what is the length of the prefix?
24
156
What is a Keepalive message in BGP?
A message exchanged regularly by routers to indicate they are alive
157
What does a notification message indicate in BGP?
An error condition or a request to close the connection
158
What does the error code field in a notification message define?
The category of the error
159
What further defines the type of error in a notification message?
The error subcode
160
What can the error data field in a notification message provide?
More diagnostic information about the error
161
What port is used for BGP messages encapsulated in TCP segments?
Port 179
162
What is the significance of encapsulating BGP messages in TCP?
There is no need for error control and flow control
163
What happens when a TCP connection is opened for BGP?
Exchange of update, keepalive, and notification messages continues until a cease message is sent
