1. Question 1. What Is Ospf Routing Protocol?

    Answer :

    Open shortest path first is an Open Standard Link State routing protocol which works by using Dijkastra algorithm to initially construct the shortest paths and follows that by populating the routing table with resulting best paths.

  2. Question 2. Mention Some Characteristics Of Ospf?

    Answer :

    1. OSPF is a classless routing protocol that supports VLSM and CIDR.
    2. It allows for creation of areas and autonomous system.
    3. OSPF uses cost as its metric, which is computed based on the bandwidth of the link.
    4. It has no hop-count limit. It supports unlimited Hop count.
    5. OSPF supports both IPV4 & IPV6.
    6. OSPF routes have an administrative distance of 110.
  3. Networking Interview Questions

  4. Question 3. What Is The Need For Dividing The Autonomous System Into Various Areas?

    Answer :

    we would divide the autonomous system into various areas to keep route updates to a minimum to conserve resources and to keep problems from propagating throughout the network.

  5. Question 4. What Is The Benefit Of Dividing The Entire Network Into Areas?

    Answer :

    The following are benefits of dividing the entire network into areas –

    1. Decrease routing overhead.
    2. Speed up convergence.
    3. Confine network instability to single areas of the network.
  6. Networking Tutorial

  7. Question 5. What Is Backbone Area?

    Answer :

    While configuring multi-area OSPF, one area must be called area 0, referred to as backbone area. All other areas must connect to backbone area as inter-area traffic is send through the backbone area.

  8. Switching Interview Questions

  9. Question 6. Explain Area Border Router(abr)?

    Answer :

    It is the router that connects other areas to the backbone area within an autonomous system. ABR can have its interfaces in more than one area.

  10. Question 7. What Is Autonomous System Border Router (asbr)?

    Answer :

    It is the Router that connects different Autonomous Systems.

  11. Veritas Volume Manager (VVM or VxVM) Interview Questions

  12. Question 8. What Is Ospf Router Id?

    Answer :

    Router Id is used to identify the Router. Highest IP address of the router’s loopback interfaces is chosen as the Router ID, If no loopback is present than highest IP address of the router’s physical interfaces will be chosen as Router ID.

  13. Question 9. What Parameters Must Match For Two Routers To Become Neighbors?

    Answer :

    The following parameters must be the same on both routers in order for routers to become neighbors:-

    1. Subnet
    2. Area id
    3. Hello and Dead interval time
    4. Authentication
  14. Cisco Nexus switches Interview Questions

  15. Question 10. How Ospf Dr & Bdr Is Elected?

    Answer :

    • The router with the highest priority becomes the DR and router with second highest priority becomes the BDR. If there is a tie in priority, router with the highest Router ID will become DR.
    • By default priority on Cisco routers is 1. We can manually change it.
    • If the Router priority is set to 0 (Zero), that router will not participate in DR/BDR election.
    • DR election process is not preemptive. If a router with a higher priority is added to the network, it will not become DR untill we clear OSPF process and DR/BDR election takes place again.

    Command to change the priority on an interface

    router(config)# interface fa0/0

    router(config-if)# ip ospf priority 100

  16. Question 11. Why Dr And Bdr Are Elected In Ospf?

    Answer :

    All OSPF routers will form adjacencies with the DR and BDR. If link-state changes, the update will be sent only to the DR, which then forwards it to all other routers. This greatly reduces the flooding of LSAs therefore conserving the bandwidth.

  17. Border Gateway Protocol (BGP) Interview Questions

  18. Question 12. Explain The Various Ospf States?

    Answer :

    OSPF routers need to go through several states before establishing a neighbor relationship:-

    1.Down – No Hello packets have been received on the interface.

    2.Attempt – In Attempt state neighbors must be configured manually. It applies only to nonbroadcast multi-access (NBMA) networks.

    3.Init state – Router has received a Hello message from the other OSFP router.

    4.2way state – The neighbor has received the Hello message and replied with a Hello message of his own. Bidirectional Communication has been established. In Broadcast network DR-BDR election can occur after this point.

    5.Exstart state – DR & BDR establish adjacencies with each router in the network. Master-slave election will takes place (Master will send its DBD first).

    6.Exchange state – Routing information is exchanged using DBD (Database Descriptor) packets, Link-State Request (LSR). Link-State Update packets may also be sent.

    7.Loading state – LSRs (Link State Requests) are send to neighbors for every network it doesn’t know about. The Neighbor replies with the LSUs (Link State Updates) which contain information about requested networks. The requested information have been received, other neighbor goes through the same process

    8.Full state – All neighbor routers have the synchronized database and adjacencies has been established.

  19. Networking Interview Questions

  20. Question 13. Explain Ospf Lsa, Lsu And Lsr?

    Answer :

    The LSAs (Link-State Advertisements) are used by OSPF routers to exchange routing and topology information. When two neighbors decide to exchange routes, they send each other a list of all LSA in their respective topology database. Each router then checks its topology database and sends Link State Request (LSR) message requesting all LSAs that was not found in its topology table. Other router responds with the Link State Update (LSU) that contains all LSAs requested by the neighbor.

  21. Question 14. What Are The Steps Required To Change Neighborship Into Adjacency?

    Answer :

    1. Two-way communication (using Hello Protocol)
    2. Database Synchronization which means exchange of Database Description (DD) packets, Link State Request (LSR) packets, Link State Update (LSU) packets.
    3. After Database synchronization is complete, the two routers are considered adjacent.
  22. Question 15. Explain Ospf Timers?

    Answer :

    Hello interval – This defines how often OSPF router will send the hello packet to other OSPF router.

    Dead interval – This defines how long a router will wait for hello packets before it declares the neighbor dead.

  23. Enhanced Interior Gateway Routing Protocol (EIGRP) Interview Questions

  24. Question 16. What Is The Default Hello Interval?

    Answer :

    The default Hello Interval for OSPF is 10 seconds.

  25. Question 17. What Is The Default Dead Interval?

    Answer :

    The Dead Interval is four times the Hello Interval. By default it is 40 seconds.

  26. Virtual Private Network (VPN) Interview Questions

  27. Question 18. What Multicast Address Does Ospf Use?

    Answer :

    OSPF use the multicast address of 224.0.0.5 & 224.0.0.6.

  28. Switching Interview Questions

  29. Question 19. Tables Maintained By Ospf?

    Answer :

    Router participating in OSPF routing protocol maintains three OSPF tables:-

    1.Neighbor table – Stores information about OSPF neighbors.

    command to see # sh ip ospf neighbor

    2.Topology table – Stores the topology structure of a network.

    command to see # sh ip ospf topology

    3.Routing table – Stores the best routes to all known networks.

    command to see # sh ip route ospf

  30. Question 20. What Are Different Ospf Lsa Types ?

    Answer :

    1. Router LSA (Type1) – Each router generates a Type 1 LSA that lists its active interfaces, IP addresses, neighbors and the cost. LSA Type 1 is flooded only within an area.
    2. Network LSA (Type2) – Type 2 LSA is sent out by the designated router (DR) and lists all the routers on the segment it is adjacent to. Type 2 LSA are flooded only within an area. It contains the information about DR’s.
    3. Summary LSA (Type3) – Type 3 LSAs are generated by Area Border Routers (ABRs) to advertise networks from one area to the rest of the areas in Autonomous System. It contains the information about inter-area routes.
    4. Summary ASBR LSA (Type4) – It is generated by the ABR and contain routes to ASBRs.
    5. External LSA (Type5) – External LSAs are generated by ASBRs and contain routes to networks that are external to current AS.
    6. Not-So-Stubby Area LSA (Type7) – Stub areas do not allow Type 5 LSAs. A Not So Stubby Area (NSSA) allows advertisement of Type 5 LSA as Type 7 LSAs. Type LSA is generated by an ASBR inside a Not So Stubby Area (NSSA) to describe routes redistributed into the NSSA.
  31. Cisco Network Engineer Interview Questions

  32. Question 21. How Do We Configure Ospf Routing Protocol?

    Answer :

    router(config)# router ospf 10

    router(config-router)# network 12.1.1.0 0.0.0.255 area 0

    router(config-router)# network 23.1.0.0 0.0.255.255 area 1

    router(config-router)# exit

    • Router ospf 10 command enables the OSPF process. Here “10” indicates the OSPF process ID and can be different on neighbor routers. Process ID allows multiple OSPF processes to run on the same router.
    • Second command configures 12.1.1.0/24 network in area 0.
    • Third command configures 23.1.0.0/16 network in area 1.

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What is VLAN?

By default, all ports on a switch are in the same broadcast domain. A Virtual Local Area Network, Virtual LAN, or VLAN, can be used to divide a single broadcast domain to multiple broadcast domains in a layer 2 switched network.

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.

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What are the VLAN membership types?

Static VLANs & Dynamic VLANs

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What is Static VLAN?

In a static VLAN, the network administrator creates a VLAN and then assigns switch ports to the VLAN. Static VLANs are also called port based VLANs. The association with the VLAN does not change until the administrator changes the port assignment. End-user devices become the members of VLAN based on the physical switch port to which they are connected.

  • Ø The ports on a single switch can be assigned multiple VLANs. Even though two devices are connected to different ports on a same switch, traffic will not pass between them if the connected ports are on different VLANs. We need a layer 3 device (typically a Router) to enable communication between two VLANs.

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What is Dynamic VLAN?

In a dynamic VLAN, the switch automatically assigns the port to a VLAN using information from the user device like MAC address, IP address etc. When a device is connected to a switch port the switch queries a database to establish VLAN membership. A network administrator must configure VLAN database of a VLAN Membership Policy Server (VMPS).

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What are the types of VLAN connection links?

There are two types of VLAN connection links and they are Access link and Trunk link.

Click on the Image to see it

The solid lines in above picture are access links and dotted line connecting two switches together is a trunk link. The access links are part of only one VLAN and carry traffic to only the end devices connected to that particular VLAN. But a trunk link is used to connect switches to other switches or to routers and can carry traffic from multiple VLANs.

Routing And Switching Interview Questions Pdf

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What is VLAN Frame Tagging?

To identify the VLAN that a frame belongs to, Cisco switches support different identification techniques (VLAN Frame tagging).

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What are the different VLAN Frame tagging techniques?

• Inter-Switch Link (ISL): Cisco proprietary VLAN frame tagging. No much support from other vendors. Supported only in old Cisco Switch models.

• IEEE 802.1Q: IEEE industry standards VLAN frame tagging.

• LAN Emulation (LANE): LANE is used to communicate with multiple VLANs over ATM.

• 802.10 (FDDI): Protocol for sending VLAN information over FDDI.

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What is Native VLAN?

Interview

Normally a Switch port configured as a trunk port send and receive IEEE 801.q VLAN tagged Ethernet frames.

If a switch receives untagged Ethernet frames on its Trunk port, they are forwarded to the VLAN that is configured on the Switch as native VLAN. Both sides of the trunk link must be configured to be in same native VLAN.

Routing And Switching Interview Questions Pdf Answers

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What is VTP?

VLAN Trunking Protocol (VTP) is used to communicate VLAN information between switches in the same VTP domain.

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What is VTP Domain?

  • Ø A VLAN Trunking Protocol (VTP) domain is one switch or several interconnected switches sharing the same VLAN Trunking Protocol (VTP) environment.
  • Ø A switch can be configured only in one VLAN Trunking Protocol (VTP) domain.
  • Ø Switches in different VTP domains do not share VLAN Trunking Protocol (VTP) information.

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What are the VLAN Trunking Protocol (VTP) Modes?

A network switch, which is participating in VLAN Trunking Protocol (VTP), can have three different modes.

Routing And Switching Interview Questions And Answers Pdf

• Server Mode

• Client Mode

• Transparent Mode

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Routing And Switching Interview Questions Pdf

What is VTP Server Mode?

VLAN Trunking Protocol (VTP) Server mode is the default VTP mode for all Catalyst switches.

At least one Server is required in a VTP domain to propagate VLAN information within the VTP domain.

We can create, add, or delete VLANs of a VTP domain in a Switch which is in VTP Server mode.

The changes made in a switch in server mode are advertised to the entire VTP domain.

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What is VTP Client Mode?

VLAN Trunking Protocol (VTP) client mode switches listen to VTP advertisements from other switches and modify their VLAN configurations accordingly.

Switching

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What is VTP Transparent Mode?

VLAN Trunking Protocol (VTP) transparent mode switches do not participate in the VTP domain, but VTP transparent mode switches can receive and forward VTP advertisements through the configured trunk links.

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What is VTP Pruning?

VLAN Trunking Protocol (VTP) pruning is a feature in Cisco switches, which stops VLAN update information traffic from being sent down trunk links if the updates are not needed.

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