Rashmi Bhardwaj | Interview Questions

Question 1 –
Can we use OSPF without backbone area?

Answer 1 –
Yes, but it will be limited to intra-area (same area) communication. By default, Inter-area communication is not possible without backbone area.
Question 2 –
What will be the status of Interface Fa0/2 of Catalyst Switch in the below 3 scenarios –





Answer 2 –
a) Blocked (Since Higher Port ID than fa0/1).
b) Err-disabled (due to bpduguard).
c) Loop in network since BPDU filter will filter the BPDUs and allow traffic to flow without blocking the… hence a loop in the network.
Question 3 –
Router A and Router B are running RIP V2 .Router B is configured to advertise all connected interfaces via RIP v1.Which networks connected to Router B will be advertised to Router A ?


Answer 3 – and
Question 4 –
Router A and Router B are running RIP V2 .Router B is configured to advertise all connected interfaces via RIP v1.Which networks connected to Router B will be advertised to Router A ?


Answer 4 –
Note – is a supernet of /24 network. advertising any network prefix less than its classful major network) is not allowed in RIP route summarization
Question 5 –
A new switch configured as a VTP client, and added to the existing VTP domain. Shortly after switch is connected, the whole network goes down. What could have caused this to happen?

Answer 5 –
The configuration revision of the switch inserted was higher than the configuration revision of the VTP domain
Question 6 –
I want to use extended VLANs (VLAN IDs 1006-4094) on network switches. What should he VTP mode be set to before configuring extended-range VLANs?

Answer 6 –
Transparent mode

Explanation –
The switch must be in VTP transparent mode when you create extended-range VLANs.Only transparent mode support extended Vlans.Server and Client mode don’t allow to store in vlan database.
Question 7 –
How much data can be carried in a standard Ethernet frame?
1500 bytes or 1518 bytes

Answer 7 
1518 bytes
Explanation –
A standard Ethernet frame MTU is 1500 bytes.  The MTU size or packet size refers only to Ethernet payload. Ethernet frame size refers to the whole Ethernet frame, including the header  and  the  trailer.
Preamble is not calculated in frame size so DA (6 bytes) SA (6 bytes) Type (2
bytes) data + pad (1500 bytes) FCS (4bytes) = a total of 1518

Note –
A standard Ethernet frame MTU is 1500 bytes. This does not include the Ethernet header and Cyclic Redundancy Check (CRC) trailer, which is 18 bytes in length, to make the total Ethernet frame size of 1518.  So the total size of an Ethernet packet can be as large as 1518 bytes, but the maximum payload is only 1500 bytes.
Question 8 –
802.1Q trunking uses which Ethertype to identify itself?

Answer 8 –
The IEEE 802.1Q specification defines the Ethertype field to be 8100 in the presence of a VLAN ID.
Question 9–
What option is the best way to apply CIDR if a service provider wants to summarize the following addresses:,,,,,

Answer 9 –,,
Explanation –
The Network will encompass the, and networks.  The second summarization, will take care of both the and networks.  Finally, the last network is needed in order to include the only remaining network, which is  This will summarize all 6 networks using only 3 statements.

Under the OSPF process, you type in the “area 1 range” command. Which LSA types will be summarized?

Answer 10 –
A, B
Explanation –

Area range command is used for summarizing routes on the boundary of two OSPF areas.The  information  to  be  summarized  is  contained  in  two  types  of  LSAs:    Type  1  and Type2.  Type  1  LSAs  are  Router  LSAs  and  are  generated  by  each  router  in  an  OSPF network.  Type 2 LSAs are network LSAs, which are generated by the DR.Both Type1 and Type 2 LSAs are flooded within the originating area only. Only when the information needs to be conveyed to another area in a summarized form area-range command is used, which acts on the information provided by these two LSAs.
which 3 BGP attributes will be carried in every BGP update(both IBGP and EBGP)?

Answer 11 –
Origin, AS-Path, Next Hop

Question 12 –

Router A,B and C are running EIGRP and are EIGRP neighbors.
Router A configuration is shown below –
Router eigrp 1
Redistribute connected

Which routes would show up  in  the  routing  table  of  Router B as EIGRP routes?

Answer 12 – and
Question 13 –
From the perspective of below diagram, which routers will met he feasibility condition for network

Answer 13 –
Router B and Router C.

Question 14 –
From the perspective of below diagram, which routers will be considered –
a)      Successor
b)      Feasible Successor
For network

Answer 14 –
Successor is Router B
Feasible Successor is Router C

Question 15 –

The “Show IP EIGRP neighbor” command is issued on the router A. Router A is configured with the default EIGRP settings. After issuing this command, which of the following RED value is incorrect ?

R1# show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H   Address                 Interface       Hold                     Uptime     SRTT   RTO       Q             Seq

(sec)                                       (ms)                   Cnt         Num

0             Fa0/0             103                        00:01:44   95          570       0              3

Answer 15 –
Hold Time should be between 10-15 and not 103 seconds.

Question 16 –
Which IP address maps to the Ethernet multicast MAC address of 01-00-5e-10-20-02 ?

Answer 16 –

Ethernet interfaces map the lower 23 bits of the IP multicast address to the lower 23 bits of the MAC 0100.5e00.0000.  As an example, the IP multicast address is Mapped to the MAC layer as 0100.5e00.0002. HEX 01 = 00-5e (all Multicast Addresses);HEX 10 = 00010000 – could be both 16 and 144 (decimal) due to the fact that we ignore the first bit of the second octet when converting to binary; HEX 20 = 00100000 = 32; HEX 02 = 00000010 = 2

What is the primary purpose for the RPF check in IP multicast networks?

Answer 17 –
To prevent multicast traffic looping through the network.

Explanation – Reverse Path Forwarding (RPF) provides loop avoidance.  It is an algorithm used to forward multicast packets.  The RPF rules are: If a router receives a datagram on an interface that it uses to send unicast packets to the source of that packet, then the packet has arrived on the RPF interface. If the packet arrives on the RPF interface, a router forwards the packet out the interfaces that are present in the outgoing interface list of a multicast routing table entry. If the packet does not arrive on the RPF interface, the packet is silently discarded.

Question 18 –
In an MPLS network, which protocol is used to distribute traffic engineering information?

Answer 18 – 
OSPF Opaque LSAs or IS-IS TLVs
OSPF Opaque LSA provides a generalized mechanism for OSPF to carry additional information. The new information can be used directly by OSPF or indirectly by other applications, which use OSPF to distribute information.

Question  19 –
What is penultimate hop popping (PHP) and what is its use?

Answer 19 –
PHP is the technique for removing the (POP) MPLS label before the egress router. The MPLS label on a switched packet is popped by either the egress router or the penultimate router, depending on your configuration. If you decide to use penultimate hop popping, you essentially terminate the LSP one hop earlier. The MPLS labels are popped by the routers that connect to the egress router, rather than all of them being popped by the same egress router.

Question 20 – Explain BGP “Site of Origin” Attribute ?

Answer 20 –

Site of Origin BGP Community Attribute
The site-of-origin (SoO) extended community is a BGP extended community attribute that is used to identify routes that have originated from a site so that the advertisement of that prefix back to the source site can be prevented. The SoO extended community uniquely identifies the site from which a router has learned a route. BGP can use the SoO value associated with a route to prevent routing loops.




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