IP ROUTING - INTERVIEW QUESTIONS (Part 2)

Question- 1 What happen if routing table does not show a route to destination network or default route ?

If routing table does not show a route to destination network or default route. the router will discard the packet and send an ICMP destination unreachable message back out to interface by which it receive the packet or packet source address.

Question- 2 What happen if routing table does not show a route to destination network but default route configured ?

If routing table does not show a route to destination network but default route configured then router will send the packet to default network.

Question- 3 What is the use of TCP port no. in transport layers ?

TCP port numbers are used to direct the data to the correct application window.

Question- 4 What is DNS ?

DNS is Domain Name System Protocol, it is used to resolve the host name into IP address. This is also known as host name to IP address resolution protocol.

Question- 5 What is ARP ?

ARP is Address Resolution protocol, it is used to resolve the IP address (Software Address) into MAC Address (Hardware Address). This is also known as Software Address to Hardware Address Resolution Protocol.

Question- 6 What is use of "logging synchronous" , "no ip domain lookup" and "sh controller" commands in CLI ?

Logging Synchronous - It stops annoying console messages from popping up and disrupting the input you’re trying to type. The messages still pop up, but you are returned to your router prompt without your input interrupted.

No IP Domain Lookup - If you have a lot of devices and don’t want to create a host table in each device, you can use a DNS (Domain Name System is used to resolve the host-name into IP address, this is also known a host name to IP address resolution protocol) to resolve host-names. Any time a Cisco device receives a command it doesn’t understand, it will try to resolve it through DNS by default. Watch what happens when I type the special command anubhav at a Cisco router prompt:

Corp#anubhav

Translating "anubhav"...domain server (255.255.255.255)

% Unknown command or computer name, or unable to find

computer address

Corp#

It doesn’t know my name or what command I am trying to type, so it tries to resolve this through DNS. This is really annoying for two reasons: first, because it doesn’t know my name "anubhav" and second, because I need to hang out and wait for the name lookup to time out. You can get around this and prevent a time-consuming DNS lookup by using the no ip domain-lookup command on your router from global configuration mode.

Sh Controller command - It is used to identify cable connection type DCE (Data Communication Equipment) or DTE (Data Terminal Equipment)

Question- 7 What is dot11 radio interface and how can we configure this interface on router ?

Dot11Radio is a wireless interface

Configuration of Dot11Radio
Router(config-if)#INT DOT11RADIO0/0/0
Router(config-if)#DESCRIPTION WLAN FOR MOBILE USER
Router(config-if)#IP ADDRESS 172.16.10.1 255.255.255.0
Router(config-if)#NO SHUT
Router(config-if)#DOT11 SSID ADMIN
Router(config-if-ssid)#GUEST-MODE
Router(config-if-ssid)#AUTHENTICATION OPEN
Router(config-if-ssid)#INFRASTRUCTURE-SSID

SSID is the Service Set Identifier that creates a wireless network that hosts can connect to. Unlike access points, the interface on the R3 router is actually a routed interface, which is the reason the IP address is placed under the physical interface—typically, if this was an access point only and not a router, the IP address would be placed under the Bridge-Group Virtual Interface (BVI), which is a logical management interface.

Guest-mode line means that the interface will broadcast the SSID so wireless hosts will understand that they can connect to this interface.

Authentication open means just that no authentication. (Even so, you still have to type that command in at minimum to make the wireless interface work.)

Infrastructure-ssid indicates that this interface can be used to communicate to other access points, or other devices on the infrastructure—to the actual wired network itself.

Question- 8 What is DHCP and how can we configure this interface ?

Dynamic Host Configuration Protocol (DHCP) assigns IP addresses to hosts.
We need to configure the DHCP pool for the wireless clients connecting to the Dot11Radio0/0/0 interface, so let’s do that now:

Router#CONFIG T
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#IP DHCP POOL Admin
Router(dhcp-config)#NETWORK 172.16.10.0 255.255.255.0
Router(dhcp-config)#DEFAULT ROUTER 172.16.10.1
Router(dhcp-config)#IP NAME-SERVER 172.16.10.4
Router(config)#IP DHCP EXCLUDED-ADDRESS 172.16.10.1 172.16.10.10

To create the DHCP server on a router, you will have to follow these steps.

Step-1 Set the pool name - IP DHCP POOL Admin

Step-2 Add the network with subnet - NETWORK 172.16.10.0 255.255.255.0

Step-3 Add the default gateway - DEFAULT ROUTER 172.16.10.1

Step-4 Add a DNS server - IP NAME-SERVER 172.16.10.4

Step-5 And exclude any addresses you don’t want handed out (like the default gateway address), and you’d usually add a DNS server as well. These exclusions are configured from global config mode, not within the DHCP pool config. In the preceding example, I excluded 172.16.10.1 through 172.16.10.10 from being assigned by the DHCP server as valid IP addresses to DHCP clients. DHCP EXCLUDED-ADDRESS 172.16.10.1 172.16.10.10

Question - 9 Which type information DHCP Server can provide ?

list of the information a DHCP server can provide:

IP address
Subnet mask
Domain name
Default gateway (routers)
DNS server address
WINS server address

Question- 10 What is the use of "sh ip dhcp binding" command ?

You can verify the DHCP pool with the show ip dhcp binding command:
Router#sh ip dhcp binding
IP address Client-ID/Hardware Address Lease expiration Type 172.16.10.11 0001.96AB.8538 -- Automatic

And of course, you can verify the client with the ipconfig command.
PC>ipconfig /all
Physical Address................: 0001.96AB.8538
IP Address......................: 172.16.10.11
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 172.16.10.1
DNS Servers.....................: 172.16.10.2

Question- 11 What is default routing ?

We use default routing to send packets with a remote destination network not in the routing table to the next-hop router.

Question- 12 Where we should use default routing and why ?

You should only use default routing on stub networks—those with only one exit path out of the network.
If you tried to put a default route on a router that isn’t a stub, it is possible that packets wouldn’t be forwarded to the correct networks because they have more than one interface routing to other routers. You can easily create loops with default routing, so be careful!

Question- 13 How to configure default route ?

To configure a default route, you use wildcards in both the network address and mask locations of a static route.

Question- 14 Why we use IP classless command in default route ?

All Cisco routers are classful routers, meaning they expect a default subnet mask on each interface of the router. When a router receives a packet for a destination subnet that’s not in the routing table, it will drop the packet by default. If you’re using default routing, you must use the ip classless command because it is possible that no remote subnets will be in the routing table.

Question- 15 Why we use the "IP default network command" ?

The ip default-network command would advertise the default network you configured on your border router when you configure an Interior Gateway Protocol (IGP), like RIP (like RIP) on the router.
This is so other routers in your inter-network will receive this route as a default route automatically

Anubhav Upadhyay

Hello and welcome to networktopic Blog. My name is Anubhav. I am a Senior Network Egineer. I have created this blog specially to serve interview questions and answer on Network Routing and Switching, I will try my best to serve correct and updated networking knowledge for you as per my corporate experience.

2 comments:

AMIT KUMAR SONIApril 14, 2020 at 11:47 PM
Very helpful post..
Thanks Anubhav

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