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68 Cards in this Set

  • Front
  • Back
Formed when two neighboring routers have exchanged information and have the same topology table
A group of routers that share the same area ID.
Routers that share the same routing protocol within the organization.
Autonomous system
The metric for OSPF.
Database descriptor: These
are packets exchanged between neighbors during the exchange state.
The DDPs contain partial LSAs, which summarize the links of everyrouter in the neighbor’s topology table.
Router responsible for making adjacencies with all neighbors on a multiaccess network,
Designated router (DR)
what is used to calculate SPF?
Dijkstra algorithm
Exchange state
State in which two neighboring routers discover the map of the network. When these routers become adjacent, they must firstexchange DDPs to ensure that they have the same topology table.
Exstart state
State in which the neighboring routers determine the sequence
number of the DDPs and establish the master/slave relationship.
Fully adjacent
When the routing tables of the two neighbors are fully synchronized,with exactly the same view of the network.
Init state
State in which a hello packet has been sent from the router, which is
waiting for a reply to establish two-way communication.
Link-state advertisement (LSA)
A packet describing a router’s links and the state of those links.
Link-state database
the link-state database has a
map of every router, its links, and the state of the links.
When the router receives a DDP complete with a partial LSA, it compares the summarized information against the topological database. If either the LSA entry is not present or the entry is older than the DDP, it will request further information.
Update sent in response to the LSR. It is the LSA that was requested.
Loading state
State in which, if the receiving router requires more information during the process in which two routers are creating an adjacency, it will request that particular link in more detail using the LSR packet.
The LSR will prompt the master router to send the LSU packet. This
is the same as an LSA used to flood the network with routing
information. While the receiving router is awaiting the LSUs from its neighbor, it is in the loading state.
A table built from the hello messages received from the neighbors.
Neighbor table
A Cisco tool by which the DR can be manually elected or, conversely, prevented from taking part in the DR/BDR election.
SPF tree
A tree of the topological network. It can be drawn after the SPF
algorithm has been run. The algorithm prunes the database of alternative paths and creates a loop-free shortest path to all networks.
difference between Topology table and link-state database
;) nothing
In a topology table he _______ is at the root of the network, which is perceived from its perspective.
Two-way state
State during the process in which two routers are creating an adjacency. The new router sees its own router ID in the list of neighbors, and a neighbor relationship is established. This is the stage before routing information is exchanged.
OSPF discovers its neighbors by sending and receiving a simple protocol called
Hello protocol.
OSPF sends out a small hello packet how periodically?
10 seconds is the default
on broadcast multiaccess media
source and destination of hello packet?
source address of the router and a multicast destination
address set to AllSPFRouters (
To ensure that the link is maintained and the topology databases are up to date, what is done?
the hello protocol keeps transmitting
Advantages of Having Neighbors
* It is a mechanism for determining that a router has gone down
*Streamlined communication
*Adjacencies created between neighbors control the distribution of the routing protocol packets.
The election is determined by either _____ or _____
the highest IP address or
Router(config-if)#ip ospf priority number
In Router(config-if)#ip ospf priority number...
The number in the priority command can be set between ___
DRs are created on _____ links
the number of adjacencies required for a full mesh is ___
the number of adjacencies required for DR/BDR situation is ___
each router must form an
adjacency with every other router on the segment in ___ kind of network
FDDI ring
If one router is elected foreman of the link, responsible for maintaining adjacencies and forwarding
updates, this dramatically reduces the __________________
overhead on the network.
The priority value of 0 means _____________
that the router cannot be a
steps in election of DR:




1) All the neighbors who have a priority greater than 0 are listed.
2) The neighbor with the highest priority is elected as the BDR.
3) If there is no DR, the BDR is promoted as DR.
4) From the remaining routers, the router with the highest priority is elected as the BDR.
5) If the priority has not been configured, there will be a tie, because the default is to set the priority
to 1.
6) If there is a tie because the priority has not been configured, the highest router IDs are used.
in the hello packet what is version #
The version of OSPF, which is
currently version 2
what is the dead interval?
The dead interval is how long the router waits before it determines that a neighbor is unavailable because it has not heard a hello packet within the prescribed time, that is, four times the hello timer.
Routing tables are built in two different ways:

1) established databases have to adjust to a change
in the network
2) New router has to create the topology and forwarding databases when it enters
the network :P
Hello protocol exchange packets when?
a new router connects to a network
Hello protocol floodarea with packets when?
If a change occurs in an existing network
which five packets are used to build the table?
Hello protocol
Database descriptor
Link-state acknowledgement
The different stages or states that the router goes through while creating a neighbor relationship are:
1. The down state
2. The init state
3. The two-way state—
The different stages or states that the router goes through while exchanging routing information with
a neighbor are:
1. The exstart state
2. The exchange state
3. The loading state
4. The full state
The topology database is updated by the
The synchronization of the topology maps is ensured by
the intricate use of sequence numbers in the LSA headers.
Although RFC 2328 does not state the number of multiple, equal-cost paths that can be
used at the same time, Cisco has defined a maximum of ___ paths that can be used simultaneously
for load balancing.
Typically, a router will identify a change in the
state of one of its links for one of the following reasons(3):
■ The router loses the physical or data link layer connectivity on a connected network.
■ The router fails to hear either an OSPF Hello protocol or a data link Hello protocol.
■ The router receives an LSA update from an adjacent neighbor, informing it of the change in the network topology
When the 2500 router receives a network LSA update from the DR, it goes through the following
logical steps:
refer 16 points on page 248
OSPF identifies five distinct network types or technologies:
■ Broadcast multiaccess
■ Point-to-point
■ Point-to-multipoint
■ Nonbroadcast multiaccess (NBMA)
■ Virtual links
Broadcast multiaccess
any LAN network, such as Ethernet, Token Ring, or FDDI.
In Broadcast multiaccess
environment, OSPF sends
multicast traffic
Point-to-point technology is used where
there is only one other router directly connected to the
transmitting or receiving router
OSPF has no need for a
DR or BDR in this scenario
Point-to-multipoint is
a single interface that connects to multiple destinations.
OSPF traffic in a point-to-Multipoint Network is sent as
There is DR or BDR election in Point-to-Multipoint Network: T/F
NBMA examples are:
WAN clouds, including X.25 and Frame Relay
NBMA uses a _________ or ________ meshed network.
fully meshed or partially meshed network.
This technology requires manual configuration of the neighbors and the DR and BDR selection.
A virtual link is
a virtual connection to a remote area that does not have any connections to the
backbone (Area 0)
The OSPF network traffic is sent in ________________ across virtual links
unicast datagrams
The NBMA technology is then subdivided into two categories, under which different configuration
options are available:
■ RFC-compliant (— NBMA — Point-to-multipoint)
■ Cisco-specific (— Point-to-multipoint nonbroadcast — Broadcast
— Point-to-point)
The Frame Relay topologies include:
■ Full mesh
■ Partial mesh
■ Star, or hub and spoke
For serial interfaces with HDLC encapsulation, the default network type is ____________ and
Timers: ____________
hello 10, dead 40.
For serial interfaces with Frame Relay encapsulation, the default network type is ____________ and
Timers: ____________
hello 30, dead 120.
For serial interfaces with Frame Relay encapsulation and using point-to-point subinterfaces,, the default network type is ____________ and Timers: ____________
point-to point.
hello 10, dead 40
For serial interfaces with Frame Relay encapsulation and using point-to-multipoint
subinterfaces, the default network type is ____________ and Timers: ____________
hello 30, dead 120.