Internetworking question solutions

Self Test ==>> Practice:



1. Examine Figure 10-1. If PC-A could ping 10.0.1.2, but got a destination
  unreachable message when pinging 10.0.2.1, what could cause this issue?

 A. The connection between Router-A and Router-B is down.
B. The connection between Router-A and the hub is down.
C. The connection between Router-A and the switch is down.
D. The connection between Switch-A and PC-A is down.

ans: B


2   Examine Figure 10-1. PC-A pings 10.0.1.1 and is successful. PC-A pings 10.0.1.2
and is successful. PC-A pings 10.0.2.1 and is not successful. PC-A pings 10.0.3.1
and is successful. What could be the issue with this scenario?

A. The hub is down.
B. Switch-A is down.
C. The DNS server is down.
D. Router-A is down.

ans.  A


3.  Examine Figure 10-1. What would PC-A ping to see whether its TCP/IP protocol stack is
operational?
A. 172.0.0.1
B. 10.0.1.1
C. 10.0.1.2
D. None of the above

ans.  D


4  Examine Figure 10-1. PC-B opens up a web session to a web service running on PC-A. In the SYN/ACK, what would be the source port number in the TCP segment header?
A. 69
B. 80
C. Greater than 49,151
D. Greater than 1023


ans.  B


5.  Examine Figure 10-1. PC-B pings the DNS server. What source MAC address does DNS server’s NIC see?
A. 0000.2222.BBBB
B. 0000.2222.AAAA
C. 0000.2222.CCCC
D. 0000.3333.BBBB


ans.  A


PART B
2. The network address of 172.16.0.0/19 provides how many subnets and hosts? Write the subnet address, broadcast address, and valid host range.

Ans. X-2   I.E  13-2
        It has 2X=2^3 ===> 8 subnets
        8192-2=8190 hosts

Subnet Mask:
255.255.224.0

Broadcast Address:
172.16.31.255

valid host range.
172.16.0.1 to 172.16.31.254



3. How many hosts are available with a Class C /29 mask?

C/29 mask
N-2      3
11111000  =   /29  -2  =  8-2=  6 host/subnet

4.    What is DHCP? How it is different from BOOTP? Briefly describe the DHCP state transition diagram

ans. DHCP
        
The Dynamic Host Configuration Protocol (DHCP) is a network protocol that is used to configure network devices so that they can communicate on an IP network. A DHCP client uses the DHCP protocol to acquire configuration information, such as an IP address, a default route and one or more DNS server addresses from a DHCP server. The DHCP client then uses this information to configure its host. Once the configuration process is complete, the host is able to communicate on the internet.
The DHCP server maintains a database of available IP addresses and configuration information. When it receives a request from a client, the DHCP server determines the network to which the DHCP client is connected, and then allocates an IP address or prefix that is appropriate for the client, and sends configuration information appropriate for that client.

Difference:

• BOOTP supports a limited number of client configuration parameters called vendor extensions , while DHCP supports a larger and extensible set of client configuration parameters called options.
  
• BOOTP uses a two-phase bootstrap configuration process in which clients contact BOOTP servers to perform address determination and boot file name selection, and clients contact Trivial File Transfer Protocol (TFTP) servers to perform file transfer of their boot image. DHCP uses a single-phase boot configuration process whereby a DHCP client negotiates with a DHCP server to determine its IP address and obtain any other initial configuration details it needs for network operation.
  
• BOOTP clients do not rebind or renew configuration with the BOOTP server except when the system restarts, while DHCP clients do not require a system restart to rebind or renew configuration with the DHCP server. Instead, clients automatically enter the Rebinding state at set timed intervals to renew their leased address allocation with the DHCP server. This process occurs in the background and is transparent to the user.
  
  
  
  5.  An ISP is granted a block of addresses starting with 150.80.0.0/16. The ISP wants to distribute these blocks to 2600 customers as follows.
  a. The first group has 200 medium-size businesses; each needs 128 addresses.
  b. The second group has 400 small businesses; each needs 16 addresses.
  c. The third group has 2000 households; each needs 4 addresses.
  Design the subblocks and give the slash notation for each subblock. Find out how many addresses are still available after these allocations. 
  
  ans. 
  a.  For 128 addresses we use /25 mask. 255.255.255.128Group 1 has 200 medium size businesses150.80.0.0 /25 Subnet 1 
  150.80.0.128 /25 Subnet 2 
  150.80.1.0 /25….150.80.1.128 /25 Subnet 3
   ……..Subnet 100
  
  
  
  --->150.80.99.128 /25    upto 150.80.99.255 
  Next address is 150.80.100.0
   b. Group 2 has 400 small businesses, each needs 16 addresses…..we use /28 mask or255.255.255.240150.80.100.0 /28 Subnet 1
   150.80.100.16 /28 Subnet 2 
  150.80.100.240 /28 Subnet 16 
  …………150.80.124.240 /28 Subnet 400 [400/16=25]
   Next address is 150.80.125.0
   c. Group 3 has 2000 households each needs 4 addresses.For 4 addresses we use /30 mask or 255.255.255.252150.80.125.0 /30 Subnet 1
   150.80.125.4 /30 Subnet 2 
  150.80.125.252 /30 Subnet 64 
  150.80.155.252 /30 Subnet 1984
  31*64=1984     
  150.80.156.0 /30 Subnet 1985
   150.80.156.60 /30 Subnet 2000 
  Next address available from 150.80.156.64 
  We have used 40000 addresses out of 65536 addresses. 25536 addresses remain available
  
  
  6. You add a new workstation to your /etc/dhcpd.conf file. You're in a hurry to finish, so you save and go to lunch. When you return, your phone mail is full of user complaints that they can't access the Internet, but the local network is fine. You surmise that you
  accidentally changed something in the dhcpd.conf file. What directive should you look at first in dhcpd.conf?
  Ans.  A missing router in/etc/dhcpd.confisdk  would keep your hosts from getting the gateway address, which is required to access the internet from an external network.
  
  
  7.  The FTP server is vsFTPd. If you want to make sure it starts the next time you boot into a standard runlevel, what command should you run?
  Ans..If you want to make sure vsFTPd service starts the next time you boot into a standard run level, the check level 35 "vsftpd on" command also works.  
  
  
  8. If a host on a network has the address 172.16.45.14/30, what is the sub-network address this host belongs to?
  Ans.  A/30 regardless of class of address, has a 252 in its 4th octet. This means we have a block size of 4 and one subnets are 0,4,8,12, 16,.... Address .14 is obviously in 12 subnet.
  SO it is:  172.16. 45.12 
   
  9.
       The Network Time Protocol
  

  1.	From the /etc/ntp.conf file, there's the following directive: restrict default kod nomodify notrap nopeer noquery What directive would you add to open access to the 192.168.0.0/24 network? ________________________________________________________
  2.	What Web site is associated with the public NTP server project? ________________________________________________________

  Answers

  1.	The appropriate directive that limits access to the 192.168.0.0/24 network is restrict 192.168.0.0 mask 255.255.255.0 nomodify notrap
  2 .	Pool.ntp.org is the Web site associated with the Public Time Server project. If you've used the Date/Time Properties tool, you should be familiar with this from the Red Hat defaults. For further queries post your questions. We answer them in 24hrs. Do not forget to leave your feed back and share this with your friends if you found it useful.