Frequently asked questions -- CCNP
( Job Level-1 & Level-2 Interview Part )
1: What information must be stored in the route table?
A: At a minimum, each entry of the routing table must include a destination address and the address of a next-hop router or an indication that the destination address is directly connected.
2: What command is used to examine the route table in a Cisco router?
A: show ip route is used to examine the routing table of a Cisco router.
3: What are the two bracketed numbers associated with the non-directly connected routes in the route table?
A: The first bracketed number is the administrative distance of the routing protocol by which the route was learned. The second number is the metric of the route.
4: When static routes are configured to reference an exit interface instead of a next-hop address, in what way will the route table be different?
A: When a static route is configured to reference an exit interface instead of a next-hop address, the destination address will be entered into the routing table as directly connected.
5: What is a summary route? In the context of static routing, how are summary routes useful?
A: A summary route is a single route entry that points to multiple subnets or major IP addresses. In the context of static routes, summary routes can reduce the number of static routes that must be configured.
6: What is an administrative distance?
A: An administrative distance is a rating of preference for a routing protocol or a static route. Every routing protocol and every static route has an administrative distance associated with it. When a router learns of a destination via more than one routing protocol or static route, it will use the route with the lowest administrative distance.
7: What is a floating static route?
A: A floating static route is an alternative route to a destination. The administrative distance is set high enough that the floating static route is used only if a more-preferred route becomes unavailable.
8: What is the difference between equal-cost and unequal-cost load sharing?
A: Equal-cost load sharing distributes traffic equally among multiple paths with equal metrics.
Unequal-cost load sharing distributes packets among multiple paths with different metrics. The
traffic will be distributed inversely proportional to the cost of the routes.
9: How does the switching mode at an interface affect load sharing?
A: If an interface is fast switched, per destination load sharing is performed. If an interface is process switched, per packet load sharing is performed.
10: What is a recursive table lookup?
A: A recursive routing table lookup occurs when a router cannot acquire all the information it needs to forward a packet with a single routing table lookup. For example, the router may perform one lookup to find the route to a destination and then perform another lookup to find a route to the next hop router of the first route.
11: What are Routed Protocols ?
1: What information must be stored in the route table?
A: At a minimum, each entry of the routing table must include a destination address and the address of a next-hop router or an indication that the destination address is directly connected.
2: What command is used to examine the route table in a Cisco router?
A: show ip route is used to examine the routing table of a Cisco router.
3: What are the two bracketed numbers associated with the non-directly connected routes in the route table?
A: The first bracketed number is the administrative distance of the routing protocol by which the route was learned. The second number is the metric of the route.
4: When static routes are configured to reference an exit interface instead of a next-hop address, in what way will the route table be different?
A: When a static route is configured to reference an exit interface instead of a next-hop address, the destination address will be entered into the routing table as directly connected.
5: What is a summary route? In the context of static routing, how are summary routes useful?
A: A summary route is a single route entry that points to multiple subnets or major IP addresses. In the context of static routes, summary routes can reduce the number of static routes that must be configured.
6: What is an administrative distance?
A: An administrative distance is a rating of preference for a routing protocol or a static route. Every routing protocol and every static route has an administrative distance associated with it. When a router learns of a destination via more than one routing protocol or static route, it will use the route with the lowest administrative distance.
7: What is a floating static route?
A: A floating static route is an alternative route to a destination. The administrative distance is set high enough that the floating static route is used only if a more-preferred route becomes unavailable.
8: What is the difference between equal-cost and unequal-cost load sharing?
A: Equal-cost load sharing distributes traffic equally among multiple paths with equal metrics.
Unequal-cost load sharing distributes packets among multiple paths with different metrics. The
traffic will be distributed inversely proportional to the cost of the routes.
9: How does the switching mode at an interface affect load sharing?
A: If an interface is fast switched, per destination load sharing is performed. If an interface is process switched, per packet load sharing is performed.
10: What is a recursive table lookup?
A: A recursive routing table lookup occurs when a router cannot acquire all the information it needs to forward a packet with a single routing table lookup. For example, the router may perform one lookup to find the route to a destination and then perform another lookup to find a route to the next hop router of the first route.
11: What are Routed Protocols ?
A: Routed protocols are the actual carriers of the data. Eg. IP ( Internet Protocol ), IPX ( Internetwork Packet Exchange ).
11: What is a routing protocol?
A: Routing Protocols help the routed protocols to reach their destination by selecting the best path.
A: Routing Protocols help the routed protocols to reach their destination by selecting the best path.
Eg- EIGRP (Enhanced Interior Gateway Routing Protocol ), OSPF (Open Shortest Path First) etc.
or
Simple Understanding is A routing protocol is a "language" that routers speak to each other to share information about network destinations.
12: Why do routing protocols use metrics?
A: A route metric, also called a route cost or a route distance, is used to determine the best path to a destination. Best is defined by the type of metric used.
13: What is convergence time?
A: Convergence time is the time a group of routers take to complete the exchange of routing
information.
14: What is a distance vector routing protocol?
A: A distance vector protocol is a routing protocol in which each router calculates routes based on the routes of its neighbors and then passes its routes to other neighbors.
15: Explain the difference between simple split horizon and split horizon with poisoned reverse.
A: Simple split horizon does not send route information back to the source of the route information. Split horizon with poisoned reverse sends the information back to the source but sets the metric to unreachable.
16: What is the counting-to-infinity problem, and how can it be controlled?
A: 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.
17: What are holddown timers, and how do they work?
A: Holddown 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 internetwork is reconverging
.
18: What are the differences between distance vector and link state routing protocols?
A: 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 internetworking 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.
19: What is the purpose of a topological database?
A: A topological database holds the link state information originated by all routers in the link state routing domain.
20: Explain the basic steps involved in converging a link state internetwork.
A: 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 internetworking 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.
21: Why are sequence numbers important in link state protocols?
A: 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 internetwork.
22: 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.
23: Explain how an SPF algorithm works.
A: 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.
24: How do areas benefit a link state internetwork?
A: 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.
25: What is an autonomous system?
A: Depending on the usage, an autonomous system can be defined as an internetwork under a common administrative domain or a single routing domain.
12: Why do routing protocols use metrics?
A: A route metric, also called a route cost or a route distance, is used to determine the best path to a destination. Best is defined by the type of metric used.
13: What is convergence time?
A: Convergence time is the time a group of routers take to complete the exchange of routing
information.
14: What is a distance vector routing protocol?
A: A distance vector protocol is a routing protocol in which each router calculates routes based on the routes of its neighbors and then passes its routes to other neighbors.
15: Explain the difference between simple split horizon and split horizon with poisoned reverse.
A: Simple split horizon does not send route information back to the source of the route information. Split horizon with poisoned reverse sends the information back to the source but sets the metric to unreachable.
16: What is the counting-to-infinity problem, and how can it be controlled?
A: 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.
17: What are holddown timers, and how do they work?
A: Holddown 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 internetwork is reconverging
.
18: What are the differences between distance vector and link state routing protocols?
A: 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 internetworking 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.
19: What is the purpose of a topological database?
A: A topological database holds the link state information originated by all routers in the link state routing domain.
20: Explain the basic steps involved in converging a link state internetwork.
A: 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 internetworking 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.
21: Why are sequence numbers important in link state protocols?
A: 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 internetwork.
22: 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.
23: Explain how an SPF algorithm works.
A: 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.
24: How do areas benefit a link state internetwork?
A: 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.
25: What is an autonomous system?
A: Depending on the usage, an autonomous system can be defined as an internetwork under a common administrative domain or a single routing domain.
good one sir and very helpful
ReplyDeleteVery Useful Blog Sir. Can you also give some Idea about CEF?
ReplyDelete