CCNA Routing Interview Question and Answer will help your to crack Interview easily. These Questions are mostly ask by Interviewer in CCNP Routing Profile.
1.What is routing?
Routing is the process in which items are forwarded from one location to another. Routing is a hop-by-hop paradigm.
A Cisco router performs routing and switching functions. Describe what each function does.
Routing is a way to learn and maintain awareness of the network topology. Each router maintains a routing table in which it looks up the destination Layer 3 address to get the packet one step closer to its destination.
The switching function is the actual movement of temporary traffic through the router, from an inbound interface to an outbound interface.
2. What are the three types of routes you can use in a Cisco router?
The three types of routes are static routes, dynamic routes, and default routes.
3.What is the difference between static and dynamic routes?
Static routes are routes that an administrator manually enters into a router. Dynamic routes are routes that a router learns automatically through a routing protocol.
4. What is a default route?
Also known as the gateway of last resort, a default route is a special type of static route with an all-zeros network and network mask. The default route is used to route any packets to a network that a router does not directly know about to a next-hop router. By default, if a router receives a packet to a destination network that is not in its routing table, it drops the packet. When a default route is specified, the router does not drop the packet. Instead, it forwards the packet to the IP address specified in the default route.
5. What is a routing protocol?
A Routing protocol defines the set of rules used by a router when it communicates with neighboring routers. Routing protocols listens for packets from other participants in order to learn and maintain a routing table.
6.What is administrative distance?
Administrative distance (AD) is an integer from 0 to 255 that rates the trustworthiness of routing information received on a router from a neighboring router. The AD is used as the tiebreaker when a router has multiple paths from different routing protocols to the same destination. The path with the lower AD is the one given priority.
7. What are the three classes of routing protocols?
1. Distance vector
3. Balanced hybrid
8. What is the AD for each of the following?
1. Directly connected interface 0
2. Static route 1
3. EIGRP 90
4. IGRP 100
5. OSPF 110
6. RIP 120
7. External EIGRP 170
8. Unknown 255
9. How do distance vector routing protocols function?
Also known as Bellman-Ford-Fulkerson algorithms, distance vector routing protocols pass complete routing tables to neighboring routers. Neighboring routers then combine the received routing table with their own routing table. Each router receives a routing table from its directly connected neighbor. Distance vector routing tables include information about the total cost and the logical address of the first router on the path to each network they know about.
10. How do distance vector routing protocols keep track of any changes to the internetwork?
Distance vector routing protocols keep track of an internetwork by periodically broadcasting updates out all active interfaces. This broadcast contains the entire routing table. This method is often called routing by rumor. Slow convergence of distance vector routing protocols can cause inconsistent routing tables and routing loops.
11.What is split horizon?
The rule of split horizon is that it is never useful to send information about a route back in the direction from which the original update came.
12. What is convergence?
Convergence is when all routers have consistent knowledge and correct routing tables.
13. What is route poisoning?
With route poisoning, when a distance vector routing protocol notices that a route is no longer valid, the route is advertised with an infinite metric, signifying that the route is bad. In RIP, a metric of 16 is used to signify infinity. Route poisoning is used with holddowns.
14. What are hold-down timers?
Hold-down timers prevent regular update messages from reinstating a route that might have gone bad. Hold-down timers also tell routers to hold for a period of time any changes that might affect routes.
15. What are triggered updates?
When a router notices that a directly connected subnet has changed state, it immediately sends another routing update out its other interfaces rather than waiting for the routing update timer to expire. Triggered updates are also known as Flash updates.
16.What is IP RIP?
IP RIP is a true distance vector routing protocol that sends its complete routing table out all active interfaces every 30 seconds. IP RIP uses a hop count as its metric to determine the best path to a remote network. The maximum allowable hop count is 15, meaning that 16 is unreachable. There are two versions of RIP. Version 1 is classful, and version 2 is classless. IP RIP can load-balance over as many as six equal-cost paths.
17. What four timers does IP RIP use to regulate its performance?
Here are the four timers that IP RIP uses to regulate its performance:
1. Route update timer Time between router updates. The default is 30 seconds.
2. Route invalid timer Time that must expire before a route becomes invalid. The default is 180 seconds.
3. Route hold-down timer If IP RIP receives an update with a hop count higher than the metric recorded in the routing table, the router goes into holddown for 180 seconds.
4. Route flush timer Time from when a route becomes invalid to when it is removed from the routing table. The default is 240 seconds.
18. How do you stop RIP updates from propagating out an interface on a router?
Sometimes you do not want RIP updates to propagate across the WAN, wasting valuable bandwidth or giving out valuable information about your internetwork. The easiest way to stop RIP updates from propagating out an interface is to use the passive-interface global configuration command.
19. How do you display the contents of a Cisco IP routing table?
The show ip route command displays the Cisco routing table’s contents.
20. What is Interior Gateway Routing Protocol (IGRP)?
IGRP is a Cisco proprietary distance vector routing protocol. IGRP has a default hop count of 100 hops, with a maximum hop count of 255. IGRP uses bandwidth and line delay as its default metric, but it can also use reliability, load, and MTU.
21. How do you enable IGRP on a Cisco router?
The way you enable IGRP on a Cisco router is similar to the way you enable RIP, except you specify IGRP as the protocol and add an autonomous system number. For example: RouterA(config)#router igrp 10 (10 is the AS number)
22. What four timers does IGRP use to regulate its performance?
The four timers IGRP uses to regulate its performance are as follows:
1. Route update timer Time between router updates The default is 90 seconds.
2. Route invalid timer Time that must expire before a route becomes invalid . The default is 270 seconds.
3. Route hold-down timer If a destination becomes unreachable, or if the next-hop router increases the metric recording in the routing table, the router goes into holddown for 280 seconds.
4. Route flush timer[md]Time from when a route becomes invalid to when it is removed from the routing table. The default is 630 seconds.
23. What are broadcast domains?
A broadcast domain defines a group of devices that receive each others’ broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower your network will be. This is because every device that receives a broadcast must process it to see if the broadcast is intended for it.
24.What devices are used to break up collision and broadcast domains?
Switches and bridges are used to break up collision domains. They create more collision domains and fewer collisions. Routers are used to break up broadcast domains. They create more broadcast domains and smaller broadcast areas.
25. How do the different layers of the OSI model communicate with each other?
Each layer of the OSI model can communicate only with the layer above it, below it, and parallel to it (a peer layer). For example, the presentation layer can communicate with only the application layer, session layer, and presentation layer on the machine it is communicating with. These layers communicate with each other using protocol data units (PDUs). These PDUs control information that is added to the user data at each layer of the model. This information resides in fields called headers (the front of the data field) and trailers (the end of the data field).
26.What does the EIGRP stuck in active message mean?
1. When EIGRP returns a stuck in active (SIA) message, it means that it has not received a reply to a query. An EIGRP neighbour (or neighbours) have not replied to the query for that route.
2. When the SIA occurs, the router clears the neighbour that did not reply to the query.
27. Why do you not see OSPF neighbours as FULL/DR or FULL/BDR on serial link?
This is normal. On point-to-point and point-to-multipoint networks, there are no designated routers (DRs) or backup designated routers (BDRs).
28. What is multicast address for EIGRP and OSPF hello packets:
1. EIGRP – 220.127.116.11
2. OSPF – for all the routers – 18.104.22.168
3. OSPF – initial multicast – only for DR and BDR – 22.214.171.124
29. What is type-1 and type-2 LSAs in OSPF?
1. Type-1 LSAs are router LSAs and are generated by each router for the area to which the router belongs.
2. Type-2 LSAs are network LSAs and are generated by the DR and BDR.
30. OSPF network types:
1. Broadcast, multi-access networks: Ehternet, token ring. Single mode operation.
2. Point-to-point : T1 CAS, ISDN BRI/PRI, single operation mode, no DR/BDR.
3. Non-broadcast multi-access(NBMA) networks: Frame realy, ATM, MPLS. Five modes of operation.
31. Explain the function of a rendezvous point ?
A RP is the focal point for multicast traffic. Traffic is forward to the RP from multicast sources. The RP then forwards traffic to multicast receivers.
32. What is the purpose of the interface command ip multicast spares-dense-mode ?
Used with PIMSM Auto-RP and version 2. if the RPs fail, the router reverts to dense mode.
33. Describe the operation of Anycast RP.
Two or more RPs are configured with the same IP address. The IP addresses of the RPs are advertised using a unicast IP routing protocol. Each multicast router chooses the closet RP. If an RP fails, the routers switch to the next nearest RP after the unicast ip routing protocol converges. The MSDP is used between RPs to exchange active multicast source information.
34. What protocols do switches use to prevent the broadcasting of multicast traffic ?
CGMP and IGMP Snooping.
35. Why are the Cisco multicast routing protocols referred to as protocol independent ?
Multicast forwarding decisions are based on the entries in the unicast IP routing table. Multicast is not dependent on how the unicast IP routing table was built; you cans use any dynamic interior routing protocol, static routes, or a combination of the two.
36.Why is BGP a better choice for Internet routing than the IGPs?
RIP version 1 and IGRP are classful protocols and do not advertise subnet mask information.
RIP version 2 has a limited network diameter of 15 hops. EIGRP, OSPF, and IS-IS use computational intensive algorithms for determining a shortest path. BGP relies on simple techniques for best path selection and loop detection, and can handle the number of network prefixes required for Internet routing.
37.What is the major difference between BGP and IGP route summarization?
When a summary address is created with an IGP (EIGRP, OSPF, and IS-IS), the specific routes of the summary are not advertised. BGP advertises the summary, and all the specific routes of the summary unless they are specifically suppressed.
38.Why does IBGP require a full mesh?
BGP uses the AS _PATH attribute for loop detection. If a router sees its own AS number in a BGP advertisement, the advertisement is dropped. IBGP routers have the same AS number so the AS number cannot be used for loop detection. IBGP neighbors will not advertise prefixes learned from one IBGP neighbor to another IBGP neighbor; therefore, a full mesh is required.
39.Name two methods for reducing the number of IBGP connections.
Route reflector and confederation.
40.What is synchronization?
Synchronization is a property of IBGP. An IBGP router will not accept a prefix received from an IBGP neighbor if the prefix is not already in the IP routing table.
41. What is the first thing that BGP checks to determine if a prefix is accessible?
BGP checks the NEXT HOP attribute to determine if the NEXT HOP is accessible or in the IP routing table.
42.Name all the ways for installing a prefix in the BGP routing table.
1. Using the network command to transfer a router from the IP routing table to the BGP routing table.
2. Redistributing routes from the IP routing table to the BGP routing table .
3. Learned from a BGP neighbor.
43.What is the order of preference for the BGP attributes AS_PATH, LOCAL_PREF, MED, and WEIGHT?
WEIGHT, LOACL_PREF, AS_PATH, MED
44.What is the purpose of the metric or MULTI_EXIT_DISC attribute?
MED is used to prefer a path into an autonomous system. A lower MED value is preferred.
45.What is the scope of the LOCAL_PREF attribute?
The LOCAL _PREF attribute is advertised throughout the autonomous system.
46.What is the purpose of the LOCAL_PREF attribute?
If a router has more than one route to the same IP prefix, the best path is the one with the highest LOCAL_PREF (assuming the WEIGHT attribute for the routes is equal).
47. What is the scope of the WEIGHT attribute?
WEIGHT has only local significance and is not advertised to BGP peers.
48. What is the purpose of the WEIGHT attribute?
If a router has more than one route to the same IP prefix, the best path is the one with the highest WEIGHT value.
49.What is the purpose of the AS_PATH attribute?
If a router has more than one route to the same IP prefix, the best path is the one with the shortest AS _PATH (assuming other BGP attributes are equal).
50.Describe four differences between the operation of IBGP and EBGP.
1. IBGP is the protocol used between routers in the same autonomous system. EBGP is the protocol used between routers in different autonomous systems.
2. IBGP routes must be synchronized before they can be transferred to the IP routing table (unless synchronization is disabled).
3. EBGP sets the next hop attribute to the IP address of the interface used to communicate with the EBGP peer. The next hop attribute is not modified when an IBGProuter advertises a prefix to an IBGP peer if the prefix was learned from an EBGP neighbor.
4. EBGP advertises all prefixes learned from an EBGP neighbor to all other EBGP neighbors. IBGP routers do not advertise prefixes learned from one IBGP neighbor to another IBGP neighbor.