CCNA CCNP are the certifications given by the CISCO company
in the level of skillset in the Networking modules. CCNA CCNP online training
is the leading online training provider for the students all over the countries
in the world. Here the training is provided by the trainers who has 12+ years
of experience in the Real time. Below are the CCNA
CCNP interview questions which help you to attend CCNA interview or cisco
certification exams.
What is the counting-to-infinity problem, and how can it be
controlled?
Answer: Counting to infinity occurs when routes update a
route over a loop; each router increases the metric of the route until the
metric reaches infinity. The effects of counting to infinity are controlled by
defining infinity as a fairly low metric so that infinity is reached fairly
quickly and the route is declared unreachable.
What are hold down timers, and how do they work?
Answer: Hold down timers help prevent routing loops. If a
route is declared unreachable or if the metric increases beyond a certain
threshold, a router will not accept any other information about that route
until the hold down timer expires. This approach prevents the router from
accepting possibly bad routing information while the inter network is re
converging.
What are the differences between distance vector and link
state routing protocols?
Answer: A distance vector router sends its entire route
table, but it only sends the table to directly connected neighbors. A link
state router sends only information about its directly connected links, but it
floods the information throughout the inter networking area. Distance vector
protocols usually use a variant of the Bellman-Ford algorithm to calculate
routes, and link state protocols usually use a variant of the Dijkstra algorithm
to calculate routes.
What is the purpose of a topological database?
Answer: A topological database holds the link state
information originated by all routers in the link state routing domain.
Explain the basic steps involved in converging a link state
inter network.
Answer: Each router floods a link state information
advertisement describing its links, the states of its links, and any
neighboring routers connected to those links, throughout the inter networking
area. All routers store all received copies of the link state advertisement in
a link state database. Each router calculates a shortest path tree from the
information in the topological database and enters routes in its routing tables
based on the shortest path tree.
Why are sequence numbers important in link state protocols?
Answer: Sequence numbers help a router differentiate between
multiple copies of the same link state advertisement and also prevent flooded
link state advertisements from circulating endlessly throughout the inter
network.
What purpose does aging serve in a link state protocol?
A: Aging prevents old, possibly obsolete, link state
information from residing in a topological database or from being accepted by a
router.
Explain how an SPF algorithm works?
Answer: A router builds a shortest path tree by first adding
itself as the root. Using the information in the topological database, the
router creates a list of all of its directly connected neighbors. The lowest
cost link to a neighbor becomes a branch of the tree, and that router’s
neighbors are added to the list. The list is checked for duplicate paths, and
if they exist, the higher-cost paths are removed from the list. The lowest-cost
router on the list is added to the tree, that router’s neighbors are added to
the list, and the list is again checked for duplicate paths. This process
continues until no routers remain on the list.
How do areas benefit a link state inter network?
Answer: Within a routing domain, areas are subdomains. They
make link state routing more efficient by limiting the size of the link state
database of each router in the area.
What is an autonomous system?
Answer: Depending on the usage, an autonomous system can be
defined as an inter network under a common administrative domain or a single
routing domain.
What is the difference between an IGP and an EGP?
Answer: An Interior Gateway Protocol is a routing protocol
that routes within an autonomous system. An Exterior Gateway Protocol is a
routing protocol that routes between autonomous systems.
What port does RIP use?
Answer: RIP uses UDP port 520.
What metric does RIP use? How is the metric used to indicate
an unreachable network?
Answer: RIP uses a hop count metric. An unreachable network
is indicated by setting the hop count to 16, which RIP interprets as an
infinite distance.
What is the update period for RIP?
Answer: RIP sends periodic updates every 30 seconds minus a
small random variable to prevent the updates of neighboring routers from becoming
synchronized.
How many updates must be missed before a route entry will be
marked as unreachable?
Answer: A route entry is marked as unreachable if six
updates are missed.
What is the purpose of the garbage collection timer?
Answer: The garbage collection timer, or flush timer, is set
when a route is declared unreachable. When the timer expires, the route is
flushed from the route table. This process allows an unreachable route to
remain in the routing table long enough for neighbors to be notified of its
status.
Why is a random timer associated with triggered updates?
What is the range of this timer?
Answer: The random timer, whose range is 1 to 5 seconds,
prevents a “storm” of triggered updates during a topology change.
Here are the CCNA
interview Questions part-1
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