What is frequently asked during interviews-Routing Technology

1. What is the OSPF joining process?
1) Send HELLO packets to each other to form two-way communication
2) Select DR/BDR Based on the Interface Network Type
3) send the first DBD and select the master and slave nodes.
4) perform DBD Synchronization
5) Interactive LSR, LSU, and LSack for LSA Synchronization
6) After the synchronization ends, enter FULL

2. Does OSPF carry complete link status packages?
LSU

3. What is the comparison between Link Status Protocol and distance vector protocol?
1) Different route transmission methods
2) Different convergence speeds
3) Different metric values
4) ring-free
5) different application environments
6) Is there a limit on the number of hops?
7) different routing Generation Algorithms
8) different device Resource Consumption

4. What are OSPF anti-ring measures?
1) SFP Algorithm without loops
2) Update the initiator information in the information and use the first-hand information
3) when there are multiple regions, the non-backbone areas must be connected to the backbone areas to connect routes. This prevents the loss of initiator information and avoids loops.

5. Is OSPF a pure link protocol?
1) a single region is a pure Link Status Protocol;
2) when there are multiple regions, the routing between regions uses the distance vector algorithm.

6. What is the meaning of DR election in OSPF? What is the network type during DR election? What is the relationship between DR and other routers?
1) Improve LSA synchronization efficiency.
2) Select DR for broadcast and NBMA
3) The DR is adjacent to other routers.

7. What is the difference between the NSSA region of OSPF and other regions?
1) compared with common regions, LSA adds seven types of LSA after removing four types of LSA.
2) compared with the STUB region, it can introduce external routes in one way.

8. who generates the LSA type of OSPF?
1) describes the direct connection topology of all LSA vrouters in the current region.
2) lsa dr describes the mask and neighbors of the CIDR block in this region.
3) three types of networks summarize the routing information of LSA associated areas and zones
4) The four types of asbrs summarize a route information for the relevant regions of the lsa abr to the ASBR.
5) Category 5 external lsa asbr overall AS external routing information
6) Seven NSSA external lsa asbr local NSSA region AS external routing information

9. Why is IBGP fully interconnected? How can I deploy the service without full interconnection?
1) solve the IBGP horizontal segmentation problem
2) reflectors or consortium

10. What are the reflection principles of Route reflectors?
1) Route Reflection from the client to all neighbors
2) Non-client routes are reflected to the client
3) Send only the optimal route
4) Two non-client routes cannot communicate with each other
5) reflection does not change route attributes

11. How does the NSSA region of OSPF communicate with other regions?

12. Why does OSPF fail to form the FULL state?
1) The HELLO Message and the expiration time are inconsistent.
2) the interface network types are inconsistent
3) Inconsistent regions
4) The Mask of the MA network is inconsistent.
5) version inconsistency
6) authentication fails
7) ROUTER-ID same
8) the priority in the MA network is 0.
9) MTU inconsistency
10) Special Area tags are different
11) bottom layer failure
12) No neighbors in the NBMA Network

13. What should I configure for OSPF IN THE NBMA network?
1) No neighbors in the NBMA Network
2) if it is a non-fully-interconnected NBMA environment, you also need to manually specify the DR
3) Considering the connectivity of branch nodes in non-fully interconnected NBMA environments, you must manually write static mappings. Or change the network type of the interface to point to multiple points.

14. When will OSPF Virtual links be used? Why use virtual links?
1) The region is not continuous or the region 0 is split.
2) because all regions must be attached to Region 0, when Region 0 is split, the routes in the two split regions 0 cannot communicate with each other.

15. What is the role of OSPF Virtual link? Why is there a backbone area?
The backbone region is set to prevent the routing between regions from generating loops when multiple regions exist.

16. How does one solve the loop problem of the RIP routing protocol?
1) horizontal segmentation
2) up to 16 hops
3) Route poisoning
4) toxicity reversal
5) suppression Timer
6) trigger update

17. What is the PPP negotiation process?
1) it is detected that the carrier enters the link establishment phase.
2) Conduct LCP negotiation
3) perform authentication
4) NCPIPCP) Negotiation

18. What is the CHAP authentication process?
1) The primary authenticated party initiates a challenge and carries the username and Random Number of the primary authenticated party.
2) The authenticated party queries the user database based on the user name, finds the corresponding password and random number for HASH, and sends the user name and HASH value
3) The primary authenticated party queries the user database based on the user name, finds the corresponding password and random number for HASH, and compares the two HASH values. If the two values are consistent, the authentication passes, and if the two values are inconsistent, the authentication fails.

19. Can an LSA5 external route be summarized on the ABR?
1) The NSSA region can be summarized on the ABR, because the NSSA region has to be divided into seven categories to five categories.
2) When there are two abr in the nssa region, it is only effective to make a summary on the large ABR of the ROUTER-ID.
3) * direct introduction of external routes to the ABR

20. What regions does OSPF have?
1) backbone Areas
2) normal area
3) The STUB area is full of STUB areas.
4) NSSA region is fully NSSA Region

21. What are the features of stub regions? What are the features of the nssa region?
1) STUB class I class II class III
2) NSSA class I class II class III Class VII do not automatically deliver default routes)
3) Full STUB class I class II class III default)
4) completely NSSA class I class III Class III default)

22. What protocol packages does OSPF have? And their roles?
1) The HELLO Message establishes a neighbor to form a 2-WAY, active, DR/BDR
2) DBD message election Master/Slave, description LSDB
3) LSR packet request LSA
4) the LSU packet sends the complete LSA
5) confirm receipt of LSACK packets LSU

23. What are the benefits of OSPF partitioning?
1) Reduce LSA flooding
2) reduced LSDB
3) Simplified route computing
4) improves the manageability of routes.
5) Make route summary and special regions possible

24. What is the CHAP authentication process?

25. OSPF routing principle; Factors Affecting OSPF neighbor formation and solutions.
1) The minimum network overhead of the target is selected.
2) by path type

26. Differences between Class 1 and Class 2 external routes of OSPF
1) overhead of type 1 = overhead + overhead
2) overhead of Type 2 = overhead
3) routes of type 1 are better than those of type 2

27. What project experiences are there and how the problems occurred during the project are solved? specific technologies include OSPF, VRRP, and VLAN tag, all questions are in-depth.

28. Is there a routing loop in the OSPF routing protocol? How to solve the routing loop? How to teach non-network industry) when users encounter OSPF networks, OSPF routers cannot form troubleshooting methods for neighbors.
1) The OSPF autonomous system has no internal routing loops, but external routing may have loops.
2) how to prevent external routes and avoid dual-point bidirectional re-publishing as much as possible. To use dual-point bidirectional re-publishing, TAG should be used for filtering to eliminate the loop.

29. What is the difference between BGP and IGP?
1) BGP is the routing protocol between AS and IGP is the routing protocol within.
2) BGP is based on TCP and can be connected to non-direct neighbors.
3) BGP focuses on route management and is not responsible for topology discovery.
4) BGP only performs incremental updates and does not perform regular updates.
5) BGP focuses on route control, while IGP focuses on Route intercommunication.

30. What is the BGP routing principle?
1) The next hop cannot be dropped.
2) discard unsynchronized loss in synchronization status
3) Select CISCO with high weight)
4) Select a local machine with a higher priority.
5) originating locally
6) The path list is short.
7) origin attributes
8) the MED value is small.
9) EBGP is better than IBGP (CISCO)
10) Small IGP overhead
11) Small ROUTER-ID
H3C
1) if the next hop of the route is not reachable, ignore the route
2) Select a route with a higher local priority
3) Select the route from the local router (with the same local priority)
4) Select a route with a shorter AS path
5) select routes of the IGP, EGP, and Incomplete types.
6) Select a smaller MED route
7) Select a route with a smaller RouterID

31. Why is full BGP connection required in the BGP network?

32. How does OSPF avoid loops?

33. How can I check whether layer-3 switching or layer-2 switching is implemented?

34. What is the role of network in OSPF? What are the special areas of OSPF when area 2 learns the routing process in area 1? What is the learning process of inter-region routing and regional external routing?
1) vrouters in area 1 send topology information to the ABR through a type of LSA, And the ABR sends route information of Area 1 to Region 0 through three types of LSA, the ABR of Area 2 learns Class 3 LAS of Area 1 from area 0 and re-generates the LAS and sends it to the vro of Area 2.
2) ASBR re-releases the external route into OSPF. Class 5 LSA is flooding in the whole AS, and Class 4 LSA will be generated for the ASBR in the region where it is located, and flood to the relevant region. An internal router can generate an external route based on the received LSA Class 4 and 5.

35. Why do IBGP neighbors not advertise routes to each other?
1) horizontal segmentation of IBGP
2) neighbor-based horizontal segmentation
3) * The route is not optimal.

36. What do you think is the concept of customer service technical support?

37. How is LSA7 spread?

38. What about BGP attributes?
Required and optional for transition and non-transition
1) Origin
2) AS-Path
3) Next hop
4) MED
5) Local-Preference
6) Community

39. What are the applications of BGP attributes in MPLS?
Routing Control

40. When a layer-3 Switch receives a packet, how does it choose layer-2 switching or layer-3 switching?

41. In OSPF, Region 1 is connected to Region 0, and Region 0 is connected to Region 2. How does region 1 route to Region 2? What solutions do you have if you do not want route entry with Region 1 in Region 2?

42. What about BGP attributes such as MED?

43. How does one learn BGP peers? Why does BGP Route synchronization be disabled?
1) Routes learned from the IBGP neighbor must be included in the IGP route table before they can be sent to the EBGP neighbor.
2) Although route synchronization can avoid routing black holes, it is difficult to implement synchronization because it is not advisable to inject BGP routes into IGP for synchronization. Therefore, to achieve route intercommunication in a non-synchronous state, only synchronization is disabled.

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