7. What protocol and port does DHCP use?
DHCP, like BOOTP runs over UDP, utilizing ports 67 and 68.
8. What is an IP address?
An IP address (also called an IP number) is a number (typically written as four
numbers separated by periods, i.e. 107.4.1.3 or 84.2.1.111) which uniquely
identifies a computer that is making use of the Internet. It is analogous to your
telephone number in that the telephone number is used by the telephone
network to direct calls to you. The IP address is used by the Internet to direct
data to your computer, e.g. the data your web browser retrieves and displays
when you surf the net. One task of DHCP is to assist in the problem of getting a
functional and unique IP number into the hands of the computers that make use
of the Internet.
9. What is a MAC address?
A MAC address (also called an Ethernet address or an IEEE MAC address) is a
number (typically written as twelve hexadecimal digits, 0 through 9 and A
through F, or as six hexadecimal numbers separated by periods or colons, i.e.
0080002012ef, 0:80:0:2:20:ef) which uniquely identifes a computer that has an
Ethernet interface. Unlike the IP number, it includes no indication of where your
computer is located. In DHCP's typical use, the server uses a requesting
computer's MAC address to uniquely identify it.
10. What is a DHCP lease?
A DHCP lease is the amount of time that the DHCP server grants to the DHCP
client permission to use a particular IP address. A typical server allows its
administrator to set the lease time.
11. What is a Client ID?
What is termed the Client ID for the purposes of the DHCP protocol is whatever
is used by the protocol to identify the client computer. By default, DHCP
implementations typically employ the client's MAC address for this purpose, but
the DHCP protocol allows other options. Some DHCP implementations have a
setup option to specify the client ID you want. One alternative to the MAC
address is simply a character string of your choice. In any case, in order for
DHCP to function, you must be certain that no other client is using the client ID
you choose, and you must be sure the DHCP server will accept it.
12.Can DHCP support statically defined addresses?
Yes. At least there is nothing in the protocol to preclude this and one expects it
to be a feature of any DHCP server. This is really a server matter and the client
should work either way. The RFC refers to this as manual allocation.
13. How does DHCP and BOOTP handle multiple subnets?
For the situations where there is more than one LAN, each with its own subnet
number, there are two ways. First of all, you can set up a seperate server on
each subnet. Secondly, a feature of some routers known as "BOOTP forwarding"
to forward DHCP or BOOTP requests to a server on another subnet and to
forward the replies back to the client. The part of such a router (or server acting
as a router) that does this is called a "BOOTP forwarding agent". Typically you
have to enable it on the interface to the subnet to be served and have to
configure it with the IP address of the DHCP or BOOTP server. On a Cisco router,
the address is known as the "UDP Helper Address".
14. Can a BOOTP client boot from a DHCP server?
Only if the DHCP server is specifically written to also handle BOOTP queries.
15. Can a DHCP client boot from a BOOTP server?
Only if the DHCP client were specifically written to make use of the answer from
a BOOTP server. It would presumably treat a BOOTP reply as an unending lease
on the IP address.
In particular, the TCP/IP stack included with Windows 95 does not have this
capability.
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