'''1. What is the effect of the first "ifconfig ethxx down" command on the system's ARP cache ?'''
Answer: The arp table becomes empty after the first "ifconfig eth1 down".
[root@localhost ~]# arp -n
'''2. What command disable ARP on a network interface?'''
Answer: To disable ARP on a network interface named 'ethxxx', one would use a command of the following form 'ifconfig ethxxx -arp'.:
ifconfig ethxxx -arp
'''3. How do you enable ARP on a network interface if it has been disabled?'''
AnswerTo re-enable ARP on a network interface named 'ethxxx', one would use a command of the following form:
To re-enable ARP on a network interface named 'ethxxx', one would use a command of the form ' ifconfig ethxxx arp'.
'''4. What is the consequence of disabling ARP on a network interface?'''
Answer: If ARP has been disabled on a network interface, ARP packets recieved by that interface will be dropped. This prevents the machine from either resolving the corresponding MAC address for a particular IP address or from responding to a requestion requisition for such resolution.
'''5. How do you manually add an entry to the ARP cache?'''
AnswerTo manually add an entry to the ARP table, one would issue a command in the following form:
To manually add an entry to the ARP table, one would isssue a command of the following form, where ' arp -s nnn.nnn.nnn.nnn xx:xx:xx:xx:xx:xx' is the MAC address you are attempting to add and 'xxx.xxx.xxx.xxx' is the corresponding IP address:
where 'arp -s xxx.xxx.xxx.xxx xx:xx:xx:xx:xx:xx'is the MAC address you are attempting to add and 'nnn.nnn.nnn.nnn' is the corresponding IP address.
'''6. What would be the possible advantage of disabling ARP on a network interface?'''
Answer: Disabling ARP on a network interface can be used to prevent a high-security server from being accessed by unauthorized hosts. While this is to some extent 'security through obscurity', in practice it is dificult difficult to guess the MAC address of the desired host if it refuses to respond to one's ARP requests. In order to make a connection to such a host the MAC addresses from both the source and destination computer are manually placed in each other's ARP cache using the command described in question 5.
'''7. Describe the procedure you used in determining the life time of an ARP cache entry on a Linux system.'''