Ch. 7 Support Services
9. Why can't a computer with an RFC 1918 IP address be used as a public-facing web server?
A computer with an RFC 1918 address cannot be used as a server because client requests will not reach it. Routers prevent packets with RFC 1918 address in the destination address from leaving the networks.
4. What is address leasing in DHCP?
Address leasing refers to the allocation of an IP address to a client for a specific duration, after which it is reclaimed by the DHCP server. The duration for which an IP address is provided is called the DHCP lease-time. Before the lease-time expires, clients can request an extension of the lease.
1. What is DHCP? Why is it useful?
DHCP, or dynamic host configuration protocol, is a technology that enables automatic assignment and collection of IP addresses. DHCP is useful because it greatly simplifies the allocation of IP addresses. DHCP also improves the efficiency of allocating IP addresses.
10. What is network address translation? Why is it useful?
Network address translation refers to changing IP addresses from one IP address block to another. It is useful because it allows computers with RFC 1918 addresses to connect to the Internet. When a packet with a RFC 1918 address reaches the NAT device, its source address is changed to a regular, routable IP address. This allows replies to the packet to reach the NAT device, which is responsible for sending it to the original source
7. What are non-routable IP addresses?
Non-routable IP addresses are addresses from the three blocks defined in RFC 1918. This allows IP address reuse. These addresses are called non-routable addresses because routers and firewalls limit the packets using RFC 1918 addresses to the LANs in which they originate. Packets do not leave any router with an RFC 1918 address in either the source IP address or destination IP address field. Routers also do not advertise routes that include RFC 1918 IP addresses to other routers because they are aware that these addresses are likely to be reused elsewhere on the network.
8. IP addresses are used for routing. Why are non-routable IP addresses useful?
Non-routable addresses are useful because they enable IP address reuse. With the help of non-routable addresses, one IP address may be used to allow hundreds of computers within a network to get Internet connectivity.
Use ipconfig /all at the command prompt of a Windows computer. What is the lease duration of the IP address?
The lease duration from my home router is 24 hours (1 day).
14. Briefly describe the operation of ARP.
When a device has a packet to send to a neighboring device whose IP address is known, it uses ARP to obtain the MAC address of the device. The sender broadcasts an ARP request packet on the network which includes the known IP address. Since the ARP request is broadcast, it is guaranteed to reach the target device. Upon receiving the ARP request, the target device replies with its MAC address. The sender can now use this address in the data link layer to form a packet and send it to the neighboring device over the LAN.
