Dhcp Faq.doc

8/8/2019 Dhcp Faq.doc

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Questions

A. General

1. What is DHCP?2. What is DHCP's purpose?

3. Who Created It? How Was It Created?4. Can DHCP work with Appletalk or IPX?5. How is it different than BOOTP or RARP?

6. How is it different than VLANs?

7. What protocol and port does DHCP use?

8. What is an IP address?9. What is a MAC address?

10. What is a DHCP lease?

11. What is a Client ID?12. Why shouldn't clients assign IP numbers without the use of a server?

13. Can DHCP support statically defined addresses?

14. How does DHCP and BOOTP handle other subnets?15. Can a BOOTP client boot from a DHCP server?

16. Can a DHCP client boot from a BOOTP server?

17. Is a DHCP server "supposed to" be able to support a BOOTP client?18. Is a DHCP client "supposed to" be able to use a BOOTP server?

19. Can a DHCP client or server make a DNS server update the client's DNS

entry to match the client's dynamically assigned address?

20. Can a DHCP server back up another DHCP server?21. When will the server to server protocol be defined?

22. Is there a DHCP mailing list?

23. In a subnetted environment, how does the DHCP server discover what

subnet a request has come from?24. If a single LAN has more than one subnet number, how can addresses be

served on subnets other than the primary one?25. If a physical LAN has more than one logical subnet, how can different

groups of clients be allocated addresses on different subnets?

26. Where is DHCP defined?

27. What other sources of information are available?28. Can DHCP support remote access?

29. Can a client have a home address and still float?

30. How can I relay DHCP if my router does not support it?31. How do I migrate my site from BOOTP to DHCP?

32. Can you limit which MAC addresses are allowed to roam?33. Is there an SNMP MIB for DHCP?34. What is DHCP Spoofing?

35. How long should a lease be?

36. How can I control which clients get leases from my server?37. How can I prevent unauthorized laptops from using a network that uses

DHCP for dynamic addressing?

38. What are the Gotcha's?
http://www.dhcp-handbook.com/dhcp_faq.html#generehttp://www.dhcp-handbook.com/dhcp_faq.html#widxxhttp://www.dhcp-handbook.com/dhcp_faq.html#widpxhttp://www.dhcp-handbook.com/dhcp_faq.html#wcihwhttp://www.dhcp-handbook.com/dhcp_faq.html#cdwwahttp://www.dhcp-handbook.com/dhcp_faq.html#hiidthttp://www.dhcp-handbook.com/dhcp_faq.html#hiidvhttp://www.dhcp-handbook.com/dhcp_faq.html#wppddhttp://www.dhcp-handbook.com/dhcp_faq.html#wiaiahttp://www.dhcp-handbook.com/dhcp_faq.html#wiamahttp://www.dhcp-handbook.com/dhcp_faq.html#wiadlhttp://www.dhcp-handbook.com/dhcp_faq.html#wiacihttp://www.dhcp-handbook.com/dhcp_faq.html#wscaihttp://www.dhcp-handbook.com/dhcp_faq.html#cdssdhttp://www.dhcp-handbook.com/dhcp_faq.html#hddhshttp://www.dhcp-handbook.com/dhcp_faq.html#cabcbhttp://www.dhcp-handbook.com/dhcp_faq.html#cadcbhttp://www.dhcp-handbook.com/dhcp_faq.html#iadsshttp://www.dhcp-handbook.com/dhcp_faq.html#iadcshttp://www.dhcp-handbook.com/dhcp_faq.html#cadcohttp://www.dhcp-handbook.com/dhcp_faq.html#cadcohttp://www.dhcp-handbook.com/dhcp_faq.html#cdsbehttp://www.dhcp-handbook.com/dhcp_faq.html#wwtsthttp://www.dhcp-handbook.com/dhcp_faq.html#istadhttp://www.dhcp-handbook.com/dhcp_faq.html#iasehhttp://www.dhcp-handbook.com/dhcp_faq.html#iasehhttp://www.dhcp-handbook.com/dhcp_faq.html#iasehhttp://www.dhcp-handbook.com/dhcp_faq.html#iaslhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaslhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaplhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaplhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaplhhttp://www.dhcp-handbook.com/dhcp_faq.html#widdxhttp://www.dhcp-handbook.com/dhcp_faq.html#wosoihttp://www.dhcp-handbook.com/dhcp_faq.html#cdsrahttp://www.dhcp-handbook.com/dhcp_faq.html#cachahttp://www.dhcp-handbook.com/dhcp_faq.html#hcirdhttp://www.dhcp-handbook.com/dhcp_faq.html#hcimfhttp://www.dhcp-handbook.com/dhcp_faq.html#cylwmhttp://www.dhcp-handbook.com/dhcp_faq.html#itasmhttp://www.dhcp-handbook.com/dhcp_faq.html#widsxhttp://www.dhcp-handbook.com/dhcp_faq.html#hlsalhttp://www.dhcp-handbook.com/dhcp_faq.html#hcicwhttp://www.dhcp-handbook.com/dhcp_faq.html#hciplhttp://www.dhcp-handbook.com/dhcp_faq.html#hciplhttp://www.dhcp-handbook.com/dhcp_faq.html#watgxhttp://www.dhcp-handbook.com/dhcp_faq.html#watgxhttp://www.dhcp-handbook.com/dhcp_faq.html#watgxhttp://www.dhcp-handbook.com/dhcp_faq.html#generehttp://www.dhcp-handbook.com/dhcp_faq.html#widxxhttp://www.dhcp-handbook.com/dhcp_faq.html#widpxhttp://www.dhcp-handbook.com/dhcp_faq.html#wcihwhttp://www.dhcp-handbook.com/dhcp_faq.html#cdwwahttp://www.dhcp-handbook.com/dhcp_faq.html#hiidthttp://www.dhcp-handbook.com/dhcp_faq.html#hiidvhttp://www.dhcp-handbook.com/dhcp_faq.html#wppddhttp://www.dhcp-handbook.com/dhcp_faq.html#wiaiahttp://www.dhcp-handbook.com/dhcp_faq.html#wiamahttp://www.dhcp-handbook.com/dhcp_faq.html#wiadlhttp://www.dhcp-handbook.com/dhcp_faq.html#wiacihttp://www.dhcp-handbook.com/dhcp_faq.html#wscaihttp://www.dhcp-handbook.com/dhcp_faq.html#cdssdhttp://www.dhcp-handbook.com/dhcp_faq.html#hddhshttp://www.dhcp-handbook.com/dhcp_faq.html#cabcbhttp://www.dhcp-handbook.com/dhcp_faq.html#cadcbhttp://www.dhcp-handbook.com/dhcp_faq.html#iadsshttp://www.dhcp-handbook.com/dhcp_faq.html#iadcshttp://www.dhcp-handbook.com/dhcp_faq.html#cadcohttp://www.dhcp-handbook.com/dhcp_faq.html#cadcohttp://www.dhcp-handbook.com/dhcp_faq.html#cdsbehttp://www.dhcp-handbook.com/dhcp_faq.html#wwtsthttp://www.dhcp-handbook.com/dhcp_faq.html#istadhttp://www.dhcp-handbook.com/dhcp_faq.html#iasehhttp://www.dhcp-handbook.com/dhcp_faq.html#iasehhttp://www.dhcp-handbook.com/dhcp_faq.html#iaslhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaslhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaplhhttp://www.dhcp-handbook.com/dhcp_faq.html#iaplhhttp://www.dhcp-handbook.com/dhcp_faq.html#widdxhttp://www.dhcp-handbook.com/dhcp_faq.html#wosoihttp://www.dhcp-handbook.com/dhcp_faq.html#cdsrahttp://www.dhcp-handbook.com/dhcp_faq.html#cachahttp://www.dhcp-handbook.com/dhcp_faq.html#hcirdhttp://www.dhcp-handbook.com/dhcp_faq.html#hcimfhttp://www.dhcp-handbook.com/dhcp_faq.html#cylwmhttp://www.dhcp-handbook.com/dhcp_faq.html#itasmhttp://www.dhcp-handbook.com/dhcp_faq.html#widsxhttp://www.dhcp-handbook.com/dhcp_faq.html#hlsalhttp://www.dhcp-handbook.com/dhcp_faq.html#hcicwhttp://www.dhcp-handbook.com/dhcp_faq.html#hciplhttp://www.dhcp-handbook.com/dhcp_faq.html#hciplhttp://www.dhcp-handbook.com/dhcp_faq.html#watgx


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B. Info on Implementations

1. What features or restrictions can a DHCP server have?

2. What freeware DHCP servers are available?3. What commercial DHCP servers are available?

4. What freeware DHCP clients are available?

5. Which vendors of client software currently support DHCP?6. What are the DHCP plans of major client-software vendors?

7. What Routers forward DHCP requests?

8. What Routers include DHCP servers?9. What Routers use DHCP to configure their IP addresses?

10. What Servers forward DHCP requests?

11. Which implementations support or require the broadcast flag?

12. What servers support secondary subnet numbers?13. What servers support RFC-based dynamic DNS update?

14. How can I run Windows 95 without a DHCP server?

15. Do any servers limit the MAC addresses that may roam?

16. What analyzers decode DHCP?17. What administration tools administer DHCP configurations?

18. How do I make a client give up its lease?19. What are the Gotcha's specific to various implementations?

Answers

A. General1. What is DHCP?

DHCP stands for "Dynamic Host Configuration Protocol".

2. What is DHCP's purpose?

DHCP's purpose is to enable individual computers on an IP network to

extract their configurations from a server (the 'DHCP server') or servers, in particular, servers that have no exact information about the individual

computers until they request the information. The overall purpose of this is

to reduce the work necessary to administer a large IP network. The mostsignificant piece of information distributed in this manner is the IP

address.

3. Can DHCP work with Appletalk or IPX?

No, it is too tied to IP. Furthermore, they don't need it since they have

always had automated mechanisms for assigning their own networkaddresses.

4. Who Created It? How Was It Created?
http://www.dhcp-handbook.com/dhcp_faq.html#infoohttp://www.dhcp-handbook.com/dhcp_faq.html#wfrcdhttp://www.dhcp-handbook.com/dhcp_faq.html#wfdsahttp://www.dhcp-handbook.com/dhcp_faq.html#wcdsahttp://www.dhcp-handbook.com/dhcp_faq.html#wfdcahttp://www.dhcp-handbook.com/dhcp_faq.html#wvocshttp://www.dhcp-handbook.com/dhcp_faq.html#watdphttp://www.dhcp-handbook.com/dhcp_faq.html#wrfdrhttp://www.dhcp-handbook.com/dhcp_faq.html#wridshttp://www.dhcp-handbook.com/dhcp_faq.html#wrudthttp://www.dhcp-handbook.com/dhcp_faq.html#wsfdrhttp://www.dhcp-handbook.com/dhcp_faq.html#wisrbhttp://www.dhcp-handbook.com/dhcp_faq.html#wsssshttp://www.dhcp-handbook.com/dhcp_faq.html#wssrdhttp://www.dhcp-handbook.com/dhcp_faq.html#hcirwhttp://www.dhcp-handbook.com/dhcp_faq.html#daslmhttp://www.dhcp-handbook.com/dhcp_faq.html#waddxhttp://www.dhcp-handbook.com/dhcp_faq.html#watadhttp://www.dhcp-handbook.com/dhcp_faq.html#hdomahttp://www.dhcp-handbook.com/dhcp_faq.html#watgohttp://www.dhcp-handbook.com/dhcp_faq.html#watgohttp://www.dhcp-handbook.com/dhcp_faq.html#watgohttp://www.dhcp-handbook.com/dhcp_faq.html#infoohttp://www.dhcp-handbook.com/dhcp_faq.html#wfrcdhttp://www.dhcp-handbook.com/dhcp_faq.html#wfdsahttp://www.dhcp-handbook.com/dhcp_faq.html#wcdsahttp://www.dhcp-handbook.com/dhcp_faq.html#wfdcahttp://www.dhcp-handbook.com/dhcp_faq.html#wvocshttp://www.dhcp-handbook.com/dhcp_faq.html#watdphttp://www.dhcp-handbook.com/dhcp_faq.html#wrfdrhttp://www.dhcp-handbook.com/dhcp_faq.html#wridshttp://www.dhcp-handbook.com/dhcp_faq.html#wrudthttp://www.dhcp-handbook.com/dhcp_faq.html#wsfdrhttp://www.dhcp-handbook.com/dhcp_faq.html#wisrbhttp://www.dhcp-handbook.com/dhcp_faq.html#wsssshttp://www.dhcp-handbook.com/dhcp_faq.html#wssrdhttp://www.dhcp-handbook.com/dhcp_faq.html#hcirwhttp://www.dhcp-handbook.com/dhcp_faq.html#daslmhttp://www.dhcp-handbook.com/dhcp_faq.html#waddxhttp://www.dhcp-handbook.com/dhcp_faq.html#watadhttp://www.dhcp-handbook.com/dhcp_faq.html#hdomahttp://www.dhcp-handbook.com/dhcp_faq.html#watgo


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DHCP was created by the Dynamic Host Configuration Working Group of

the Internet Engineering Task Force (IETF; a volunteer organization

which defines protocols for use on the Internet). As such, it's definition isrecorded in an Internet RFC and the Internet Activities Board (IAB) is

asserting its status as to Internet Standardization. As of this writing (June

1998), DHCP is an Internet Draft Standard Protocol and is Elective.BOOTP is an Internet Draft Standard Protocol and is Recommended. For

more information on Internet standardization, see RFC2300 (May 1998)

5. How is it different than BOOTP or RARP?

DHCP is based on BOOTP and maintains some backward compatibility.

The main difference is that BOOTP was designed for manual pre-configuration of the host information in a server database, while DHCP

allows for dynamic allocation of network addresses and configurations to

newly attached hosts. Additionally, DHCP allows for recovery and

reallocation of network addresses through a leasing mechanism.

RARP is a protocol used by Sun and other vendors that allows a computer

to find out its own IP number, which is one of the protocol parameters

typically passed to the client system by DHCP or BOOTP. RARP doesn'tsupport other parameters and using it, a server can only serve a single

LAN. DHCP and BOOTP are designed so they can be routed.

6. How is it different than VLANs?

DHCP and VLANs, which are very different in concept, are sometimes

cited as different solutions to the same problem. While they have a goal incommon (easing moves of networked computers), VLANs represent a

more revolutionary change to a LAN than DHCP. A DHCP server andforwarding agents can allow you to set things up so that you can unplug a

client computer from one network or subnet and plug it into another and

have it come alive immediately, it having been reconfigured

automatically. In conjunction to Dynamic DNS, it could automatically begiven its same name in its new place. VLAN-capable LAN equipment

with dynamic VLAN assignment allows you to configure things so a client

computer can be plugged into any port and have the same IP number (aswell as name) and be on the same subnet. The VLAN-capable network

either has its own configuration that lists which MAC addresses are to

belong to each VLAN, or it makes the determination from the source IPaddress of the IP packets that the client computer sends. Some differences

in the two approaches:

DHCP handles changes by reconfiguring the client while a VLAN-

capable network handles it by reconfiguring the network port theclient is moved to.


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DHCP dynamic reconfiguration requires a DHCP server,

forwarding agent in each router, and DHCP capability in each

client's TCP/IP support. The analogous capability in VLANsrequires that all hubs throughout the network be VLAN-capable,

supporting the same VLAN scheme. To this point VLAN support

is proprietary with no vendor interoperability, but standards arebeing developed.

DHCP can configure a new client computer for you while a

VLAN-capable network can't. DHCP is generally aimed at giving "easy moves" capability to

networks that are divided into subnets on a geographical basis, or

on separate networks. VLANs are generally aimed at allowing you

to set up subnets on some basis other than geographical, e.g.instead of putting everyone in one office on the same subnet,

putting each person on a subnet that has access to the servers that

that person requires.

There is an issue with trying to use DHCP (or BOOTP) and VLANs at thesame time, in particular, with the scheme by which the VLAN-capable

network determines the client's VLAN based upon the client computer's

source IP address. Doing so assumes the client computer is alreadyconfigured, which precludes the use of network to get the configuration

information from a DHCP or BOOTP server.

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 usedby 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 assistin 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 MACaddress) 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


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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 touniquely 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 serverallows 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 stringof 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. Why shouldn't clients assign IP numbers without the use of a server?

It is theoretically possible to develop software for client-machines that

finds an unused address by picking them out of the blue and broadcasting

a request of all the other client machines to see if they are using them.Appletalk is designed around this idea, and Apple's MacTCP can beconfigured to do this for IP. However, this method of IP address

assignment has disadvantages.

11 A computer that needs a permanently-assigned IP number

might be turned off and lose its number to a machine coming up.This has problems both for finding services and for security.

11 A network might be temporarily divided into two non-

communicating networks while a network component is notfunctioning. During this time, two different client-machines might

end up claiming the same IP number. When the network comesback, they start malfunctioning.

11 If such dynamic assignment is to be confined to ranges of

IP addresses, then the ranges are configured in each desktop

machine rather than being centrally administered. This can leadboth to hidden configuration errors and to difficulty in changing

the range. Another problem with the use of such ranges is keeping

it easy to move a computer from one subnet to another.


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2. 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 servermatter and the client should work either way. The RFC refers to this as

manual allocation.

3. 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 seperateserver 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 ofsuch 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 IPaddress of the DHCP or BOOTP server. On a Cisco router, the address is

known as the "UDP Helper Address".

4. Can a BOOTP client boot from a DHCP server?

Only if the DHCP server is specifically written to also handle BOOTP

queries.

5. Can a DHCP client boot from a BOOTP server?

Only if the DHCP client were specifically written to make use of theanswer 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 nothavethis capability.

6. Is a DHCP server "supposed to" be able to support a BOOTP client?

The RFC on such interoperability (1534) is clear: "In summary, a DHCP

server: ... MAY support BOOTP clients," (section 2). The word "MAY"

indicates such support, however useful, is left as an option.

A source of confusion on this point is the following statement in section

1.5 of RFC 1541: "DHCP must provide service to existing BOOTP

clients." However, this statement is one in a list of "general design goalsfor DHCP", i.e. what the designers of the DHCP protocol set as their own

goals. It is not in a list of requirements for DHCP servers.


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7. Is a DHCP client "supposed to" be able to use a BOOTP server?

The RFC on such interoperability (1534) is clear: "A DHCP client MAY

use a reply from a BOOTP server if the configuration returned from theBOOTP server is acceptable to the DHCP client." (section 3). The word

"MAY" indicates such support, however useful, is left as an option.

8. Can a DHCP client or server make a DNS server update the client's DNS

entry to match the client's dynamically assigned address?

RFCs 2136 and 2137 indicate a way in which DNS entries can be updateddynamically. Using this requires a DNS server that supports this feature

and a DHCP server that makes use of it. The RFCs are very recent (as of

5/97) and implementations are few. In the mean time, there are DNS andDHCP servers that accomplish this through proprietary means.

9. Can a DHCP server back up another DHCP server?

You can have two or more servers handing out leases for different

addresses. If each has a dynamic pool accessible to the same clients, then

even if one server is down, one of those clients can lease an address fromthe other server.

However, without communication between the two servers to share their

information on current leases, when one server is down, any client with alease from it will not be able to renew their lease with the other server.

Such communication is the purpose of the "server to server protocol" (see

next question). It is possible that some server vendors have addressed thisissue with their own proprietary server-to-server communication.

10. When will the server to server protocol be defined?

The DHC WG of the IETF is actively investigating the issues in inter-

server communication. The protocol should be defined "soon".

11. Is there a DHCP mailing list?

There are several:

List Purpose---- [email protected] General discussion: a goodlist for

server [email protected] DHCP [email protected] [email protected] Server to server [email protected] DNS-DHCP issues


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[email protected] DHCP for IPv6

The lists are run by [email protected] can be used to subscribeand sign off. Archives for the dhcp-v4 list (which used to be called the

host-conflist) are stored at ftp://ftp.bucknell.edu/pub/dhcp/.

12. In a subnetted environment, how does the DHCP server discover what

subnet a request has come from?

DHCP client messages are sent to off-net servers by DHCP relay agents,

which are often a part of an IP router. The DHCP relay agent records the

subnet from which the message was received in the DHCP message

header for use by the DHCP server.

Note: a DHCP relay agent is the same thing as a BOOTP relay agent, and

technically speaking, the latter phrase is correct.

13. If a single LAN has more than one subnet number, how can addresses be

served on subnets other than the primary one?

A single LAN might have more than one subnet number applicable to thesame set of ports (broadcast domain). Typically, one subnet is designated

as primary, the others as secondary. A site may find it necessary to support

addresses on more than one subnet number associated with a singleinterface. DHCP's scheme for handling this is that the server has to be

configured with the necessary information and has to support such

configuration & allocation. Here are four cases a server might have to

handle:

11 Dynamic allocation supported on secondary subnet

numbers on the LAN to which the server is attached.

11 Dynamic allocation supported on secondary subnetnumbers on a LAN which is handled through a DHCP/BOOTP

Relay. In this case, the DHCP/BOOTP Relay sends the server a

gateway address associated with the primary subnet and the servermust know what to do with it.

The other two cases are the same capabilities during manual allocation. It

is possible that a particular server-implementation can handle some ofthese cases, but not all of them. See section below listing the capabilitiesof some servers.

14. If a physical LAN has more than one logical subnet, how can different

groups of clients be allocated addresses on different subnets?
mailto:[email protected]:[email protected]://ftp.bucknell.edu/pub/dhcp/http://www.dhcp-handbook.com/dhcp_faq.html#wsssshttp://www.dhcp-handbook.com/dhcp_faq.html#wssssmailto:[email protected]://ftp.bucknell.edu/pub/dhcp/http://www.dhcp-handbook.com/dhcp_faq.html#wssss


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One way to do this is to preconfigure each client with information about

what group it belongs to. A DHCP feature designed for this is the user

class option. To do this, the client software must allow the user classoption to be preconfigured and the server software must support its use to

control which pool a client's address is allocated from.

15. Where is DHCP defined?

In Internet RFCs.

RFC 2131R. Droms, "Dynamic Host Configuration Protocol", 3/97. Supersedes RFC 1541

and RFC 1531. [Note that some of the references in this FAQ are to RFC 1541:I'll update them when I get a chance. -- Author]

RFC 1534

R. Droms, "Interoperation Between DHCP and BOOTP", 10/08/1993.

RFC 2132S. Alexander, R. Droms, "DHCP Options and BOOTP Vendor Extensions", 3/97.

Supersedes RFC 1533.

Some websites with copies of RFCs:

http://info.internet.isi.edu/1s/in-notes/rfc/http://www.cis.ohio-state.edu/hypertext/information/rfc.html

http://www.pmg.lcs.mit.edu/rfc.html

16. What other sources of information are available?

See the dhcp-v4 mailing list mentioned above as well as its archives.

DHCP - Dynamic Host Configuration Protocolhttp://www.eg.bucknell.edu/~droms/dhcp/

Problems and Solutions of DHCP: Experiences with DHCPimplementation and Operation

A. Tominaga, O. Nakamura, F. Teraoka, J. Murai.http://info.isoc.org/HMP/PAPER/127/html/paper.html

DHCP Resources

Alan Dobkin. http://NWS.CC.Emory.Edu/WebStaff/Alan/Net-Man/Computing/DHCP/

DHCP Reading RoomEric Hall. http://www.ehsco.com/reading/dhcp.htmlInternet Drafts

Internet drafts are works in progress intended to update the current RFCs or

specify additional functionality, and sometimes there is one or more draft relatedto DHCP. All Internet Drafts are available from various sites: the US East Cost

site is ftp://ds.internic.net/internet-drafts/; a web site is

http://ds.internic.net/ds/dsintdrafts.html. The DHCP-related drafts currently have
http://info.internet.isi.edu/1s/in-notes/rfc/http://info.internet.isi.edu/1s/in-notes/rfc/http://www.cis.ohio-state.edu/hypertext/information/rfc.htmlhttp://www.pmg.lcs.mit.edu/rfc.htmlhttp://www.pmg.lcs.mit.edu/rfc.htmlhttp://www.dhcp-handbook.com/dhcp_faq.html#istadhttp://www.eg.bucknell.edu/~droms/dhcp/http://info.isoc.org/HMP/PAPER/127/html/paper.htmlhttp://nws.cc.emory.edu/WebStaff/Alan/Net-Man/Computing/DHCP/http://nws.cc.emory.edu/WebStaff/Alan/Net-Man/Computing/DHCP/http://www.ehsco.com/reading/dhcp.htmlhttp://www.ehsco.com/reading/dhcp.htmlftp://ds.internic.net/internet-drafts/http://ds.internic.net/ds/dsintdrafts.htmlhttp://info.internet.isi.edu/1s/in-notes/rfc/http://www.cis.ohio-state.edu/hypertext/information/rfc.htmlhttp://www.pmg.lcs.mit.edu/rfc.htmlhttp://www.dhcp-handbook.com/dhcp_faq.html#istadhttp://www.eg.bucknell.edu/~droms/dhcp/http://info.isoc.org/HMP/PAPER/127/html/paper.htmlhttp://nws.cc.emory.edu/WebStaff/Alan/Net-Man/Computing/DHCP/http://nws.cc.emory.edu/WebStaff/Alan/Net-Man/Computing/DHCP/http://www.ehsco.com/reading/dhcp.htmlftp://ds.internic.net/internet-drafts/http://ds.internic.net/ds/dsintdrafts.html


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filenames of the form "draft-ietf-dhc-SOMETHING". These DHCP-related drafts

are also stored at ftp://ftp.bucknell.edu/pub/dhcp/, and are available through

http://www.eg.bucknell.edu/~droms/dhcp/. I cannot be more specific about thedocuments because they are by their nature temporary.

"DHCP Clients: Do They Really Work?"

Eric Hall.Network Computing, Vol. 7, No. 7, May 1, 1996, pp. 114-120. ReviewsDHCP-client-function of some popular Windows IP stacks.

http://www.ehsco.com/reading/19960515ncw2.html

"The Heaven And Hell Of DHCP Servers"Eric Hall. Network Computing, Vol. 7, No. 8, May 15, 1996, pp. 118-121.

Reviews DHCP servers. http://www.ehsco.com/reading/19960515ncw1.html

17. Can DHCP support remote access?

PPP has its own non-DHCP way in which communications servers can

hand clients an IP address called IPCP (IP Control Protocol) but doesn't

have the same flexibility as DHCP or BOOTP in handing out otherparameters. Such a communications server may support the use of DHCP

to acquire the IP addresses it gives out. This is sometimes called doingDHCP by proxy for the client. I know that Windows NT's remote access

support does this.

A feature of DHCP under development (DHCPinform) is a method by

which a DHCP server can supply parameters to a client that already has anIP number. With this, a PPP client could get its IP number using IPCP,

then get the rest of its parameters using this feature of DHCP.

SLIP has no standard way in which a server can hand a client an IPaddress, but many communications servers support non-standard ways ofdoing this that can be utilized by scripts, etc. Thus, like communications

servers supporting PPP, such communications servers could also support

the use of DHCP to acquire the IP addressees to give out.

The DHCP protocol is capable of allocating an IP address to a devicewithout an IEEE-style MAC address, such as a computer attached through

SLIP or PPP, but to do so, it makes use of a feature which may or may not

be supported by the DHCP server: the ability of the server to usesomething other than the MAC address to identify the client.

Communications servers that acquire IP numbers for their clients via

DHCP run into the same roadblock in that they have just one MACaddress, but need to acquire more than one IP address. One way such a

communications server can get around this problem is through the use of a

set of unique pseudo-MAC addresses for the purposes of its

communications with the DHCP server. Another way (used by Shiva) is touse a different "client ID type" for your hardware address. Client ID type 1
ftp://ftp.bucknell.edu/pub/dhcp/http://www.eg.bucknell.edu/~droms/dhcp/http://www.ehsco.com/reading/19960515ncw2.htmlhttp://www.ehsco.com/reading/19960515ncw2.htmlhttp://www.ehsco.com/reading/19960515ncw1.htmlftp://ftp.bucknell.edu/pub/dhcp/http://www.eg.bucknell.edu/~droms/dhcp/http://www.ehsco.com/reading/19960515ncw2.htmlhttp://www.ehsco.com/reading/19960515ncw1.html


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means you're using MAC addresses. However, client ID type 0 means an

ASCII string.

18. Can a client have a home address and still float?

There is nothing in the protocol to keep a client that already has a leasedor permanent IP number from getting a(nother) lease on a temporary basis

on another subnet (i.e., for that laptop which is almost always in one

office, but occasionally is plugged in in a conference room or class room).Thus it is left to the server implementation to support such a feature. I've

heard that Microsoft's NT-based server can do it.

19. How can I relay DHCP if my router does not support it?

A server on a net(subnet) can relay DHCP or BOOTP for that net.

Microsoft has software to make Windows NT do this.

20. How do I migrate my site from BOOTP to DHCP?

I don't have an answer for this, but will offer a little discussion. The

answer depends a lot on what BOOTP server you are using and how you

are maintaining it. If you depend heavily on BOOTP server software tosupport your existing clients, then the demand to support clients that

support DHCP but not BOOTP presents you with problems. In general,

you are faced with the choice:

11 Find a server that is administered like your BOOTP server

only that also serves DHCP. For example, one popular BOOTPserver, the CMU server, has been patched so that it will answer

DHCP queries.

11 Run both a DHCP and a BOOTP server. It would be good

if I could find out the gotcha's of such a setup.

11 Adapt your site's administration to one of the available

DHCP/BOOTP servers.

11 Handle the non-BOOTP clients specially, e.g. turn off

DHCP and configure them statically: not a good solution, but

certainly one that can be done to handle the first few non-BOOTPclients at your site.

21. Can you limit which MAC addresses are allowed to roam?

Sites may choose to require central pre-configuration for all computers

that will be able to acquire a dynamic address. A DHCP server could bedesigned to implement such a requirement, presumably as an option to the

server administrator. See section below on servers that implement this.

22. Is there an SNMP MIB for DHCP?
http://www.dhcp-handbook.com/dhcp_faq.html#daslmhttp://www.dhcp-handbook.com/dhcp_faq.html#daslm


12/31

There is no standard MIB; creating one is on the list of possible activities

of the DHCP working group. It is possible that some servers implement

private MIBs.

23. What is DHCP Spoofing?

Ascend Pipeline ISDN routers (which attach Ethernets to ISDN lines)

incorporate a feature that Ascend calls "DHCP spoofing" which is

essentially a tiny server implementation that hands an IP address to aconnecting Windows 95 computer, with the intention of giving it an IP

number during its connection process.

24. How long should a lease be?

I've asked sites about this and have heard answers ranging from 15

minutes to a year. Most administrators will say it depends upon your

goals, your site's usage patterns, and service arrangements for your DHCPserver.

A very relevant factor is that the client starts trying to renew the lease

when it is halfway through: thus, for example, with a 4 day lease, theclient which has lost access to its DHCP server has 2 days from when it

first tries to renew the lease until the lease expires and the client must stop

using the network. During a 2-day outage, new users cannot get newleases, but no lease will expire for any computer turned on at the time that

the outage commences.

Another factor is that the longer the lease the longer time it takes for clientconfiguration changes controlled by DHCP to propogate.

Some relevant questions in deciding on a lease time:

Do you have more users than addresses?

If so, you want to keep the lease time short so people don't end up sitting on

leases. Naturally, there are degrees. In this situation, I've heard examples cited of15 minutes, 2 hours, and 2 days. Naturally, if you know you will have 20 users

using 10 addresses in within a day, a 2 day lease is not practical.

Are you supporting mobile users?

If so, you may be in the situation of having more users than addresses on someparticular IP number range. See above.

Do you have a typical or minimum amount of time that you are trying to

support?If your typical user is on for an hour at minimum, that suggest a hour lease at

minimum.

How many clients do you have and how fast are the communications linesover which the DHCP packets will be run?


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The shorter the lease, the higher the server and network load. In general, a lease of

at least 2 hours is long enough that the load of even thousands of clients is

negligible. For shorter leases, there may be a point beyond which you will want towatch the load. Note that if you have a communication line down for a long

enough time for the leases to expire, you might see an unusually high load it

returns. If the lease-time is at least double the communication line outage, this isavoided.

How long would it take to bring back up the DHCP server, and to what

extent can your users live without it?If the lease time is at least double the server outage, then running clients who

already have leases will not lose them. If you have a good idea of your longest

likely server outage, you can avoid such problems. For example, if your server-

coverage is likely to recover the server within three hours at any time that clientsare using their addresses, then a six hour lease will handle such an outage. If you

might have a server go down on Friday right after work and may need all

Monday's work-day to fix it, then your maximum outage time is 3 days and a 6-

day lease will handle it.Do you have users who want to tell other users about their IP number?

If your users are setting up their own web servers and telling people how to get tothem either by telling people the IP number or through a permanent DNS entry,

then they are looking for an IP number that won't be changing. While some sites

would manually allocate any address that people expected to remain stable, other

sites want to use DHCP's ability to automate distribution of relatively permanentaddresses. The relevant time is the maximum amount of time that you wish to

allow the user to keep their machine turned off yet keep their address. For

example, in a university, if students might have their computers turned off for aslong as three weeks between semesters, and you wish them to keep their IP

address, then a lease of six weeks or longer would suffice.

Some examples of lease-times that sites have used & their rationals:

15 minutesTo keep the maximum number of addresses free for distribution in cases where

there will be more users than addresses.

6 hours

Long enough to allow the DHCP server to be fixed, e.g. 3 hours.12 hours

If you need to take back an address, then you know that it will only take one night

for the users' lease to expire.3 days

This is apparently Microsoft's default, thus many sites use it.

6 daysLong enough that a weekend server outage that gets fixed on Monday will not

result in leases terminating.

4 months


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Long enough that students can keep their IP address over the summer hiatus. I

believe this rational is workable if the summer hiatus is no more than 2 months.

One yearIf a user has not used their address in six months, then they are likely to be gone.

Allows administrator to recover those addresses after someone has moved on.

25. How can I control which clients get leases from my server?

There is no ideal answer: you have to give something up or do some extrawork.

You can put all your clients on a subnet of your own along with

your own DHCP server.

You can use manual allocation. Perhaps you can find DHCP server software that allows you to list

which MAC addresses the server will accept. DHCP servers that

support roaming machines may be adapted to such use. You can use the user class option assuming your clients and server

support it: it will require you to configure each of your clients with

a user class name. You still depend upon the other clients to

respect your wishes.2. How can I prevent unauthorized laptops from using a network that uses

DHCP for dynamic addressing?

This would have to be done using a mechanism other than DHCP. DHCP

does not prevent other clients from using the addresses it is set to hand outnor can it distinguish between a computer's permanent MAC address and

one set by the computer's user. DHCP can impose no restrictions on whatIP address can use a particular port nor control the IP address used by anyclient.

3. What are the Gotcha's?

A malicious user could make trouble by putting up an unofficial

DHCP server. The immediate problem would be a server passing out

numbers already belonging to some computer yielding the

potential for two or more "innocent bystander" nodesending up with the same IP number. Net result is problems

using the nodes, possibly intermittent of one or the other is

sometimes turned off. A lot of problems are possible if a renegade server manages

to get a client to accept its lease offering, and feeds the

client its own version of other booting parameters. One

scenario is a client that loads its OS over the network viatftp being directed to a different file (possibly on a different

server), thus allowing the perpetrator to take over the client.


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Given that boot parameters are often made to control many

different things about the computers' operation and

communication, many other scenarios are just as serious.

Note that BOOTP has the same vulnerabilities.

The "broadcast flag": DHCP includes a way in which client

implementations unable to receive a packet with a specific IP

address can ask the server or relay agent to use the broadcast IPaddress in the replies (a "flag" set by the client in the requests).

The definition of DHCP states that implementations "should"

honor this flag, but it doesn't say they "must". Some Microsoft

TCP/IP implementations used this flag, which meant in practicalterms, relay agents and servers had to implement it. A number of

BOOTP-relay-agent implementations (e.g. in routers) handled

DHCP just fine except for the need for this feature, thus they

announced new versions stated to handle DHCP. Some of the virtual LAN schemes, i.e., those that use the packet's

IP number to decide which "virtual LAN" a client-computer is onfor the purposes of TCP/IP, don't work when using DHCP to

dynamically assign addresses. DHCP servers and relay agents use

their knowledge of what LAN the client-station is on to select thesubnet number for the client-station's new IP address whereas such

switches use the subnet number sent by the client-station to decide

which (virtual) LAN to put the station on.

Routers are sometimes configured so that one LAN on one port hasmultiple network (or subnet) numbers. When the router is relaying

requests from such a LAN to the DHCP server, it must pass alongas IP number that is associated with one of the network (or subnet)numbers. The only way the DHCP server can allocate addresses on

one of the LAN's other network (or subnet) numbers is if the

DHCP server is specifically written to have a feature to handlesuch cases, and it has a configuration describing the situation.

The knowledge that a particular IP number is associated with a

particular node is often used for various functions. Examples are:

for security purposes, for network management, and even foridentifying resources. Furthermore, if the DNS's names are going

to identify IP numbers, the numbers, the IP numbers have to be

stable. Dynamic configuration of the IP numbers undercuts suchmethods. For this reason, some sites try to keep the continued use

of dynamically allocatable IP numbers to a minimum.

With two or more servers serving a LAN, clients that are movedaround (e.g. mobile clients) can end up with redundant leases.

Consider a home site with two DHCP servers, a remote site with

DHCP services, and a mobile client. The client first connects to thehome site and receives an address from one of the two serves.


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He/she then travels to the remote site (without releasing the lease

at the home site) and attempts to use the acquired address. It is of

course NAK'ed and the client receives an address appropriate forthe remote site. The client then returns home and tries to use the

address from the remote site. It is NAK'ed but now the client

broadcasts a DHCPDISCOVER to get a address. The server thatholds the previous lease will offer the address back to the client but

there is no guarantee that the client will accept that address;

consequently, it is possible for the client to acquire an address onthe other server and therefore have two leases within the site. The

problem can be solved by using only one server per subnet/site and

can be mitigated by short lease lengths. But in a very mobile

environment, it is possible for these transient clients to consumemore than their fair share of addresses.

If departments, offices, or individuals run DHCP servers with their

own small address pools on LANs shared by other departments,

offices, or individuals, they can find that their addresses are beingused by anyone on the LAN that happens to set their IP

configuration to use DHCP. An easy mistake to make in setting up a DHCP server is to fail to

set all the necessary global parameters. This can result in some

functions working while others are not, or functions working when

the client is set up manually, but failing to work when set to useDHCP.

Long leases can be disadvantageous in cases where you need to

change a configuration parameter or withdraw an address from use.The length of the lease can mean the difference between having to

go to every affected client and rebooting it, or merely waiting a

certain amount of time for the leases to be renewed. (Note: oneworkaround is to fool with the client computer's clock).

B. Info on Implementations

4. What features or restrictions can a DHCP server have?

While the DHCP server protocol is designed to support dynamicmanagement of IP addresses, there is nothing to stop someone from

implementing a server that uses the DHCP protocol, but does not provide

that kind of support. In particular, the maintainer of a BOOTP server-implementation might find it helpful to enhance their BOOTP server to

allow DHCP clients that cannot speak "BOOTP" to retrieve statically

defined addresses via DHCP. The following terminology has become

common to describe three kinds of IP address allocation/management.These are independent "features": a particular server can offer or not offer

any of them:


17/31

Manual allocation: the server's administrator creates a

configuration for the server that includes the MAC address and IP

address of each DHCP client that will be able to get an address:functionally equivalent to BOOTP though the protocol is

incompatible.

Automatic allocation: the server's administrator creates aconfiguration for the server that includes only IP addresses, which

it gives out to clients. An IP address, once associated with a MAC

address, is permanently associated with it until the server'sadministrator intervenes.

Dynamic allocation: like automatic allocation except that the

server will track leases and give IP addresses whose lease has

expired to other DHCP clients.

Other features which a DHCP server may or may not have:

Support for BOOTP clients. Support for the broadcast bit.

Administrator-settable lease times. Administrator-settable lease times on manually allocated

addresses.

Ability to limit what MAC addresses will be served with dynamicaddresses.

Allows administrator to configure additional DHCP option-types.

Interaction with a DNS server. Note that there are a number of

interactions that one might support and that a standard set &method is in the works.

Interaction with some other type of name server, e.g. NIS. Allows manual allocation of two or more alternative IP numbers to

a single MAC address, whose use depends upon the gateway

address through which the request is relayed.

Ability to define the pool/pools of addresses that can be allocateddynamically. This is pretty obvious, though someone might have a

server that forces the pool to be a whole subnet or network. Ideally,

the server does not force such a pool to consist of contiguous IP

addresses. Ability to associate two or more dynamic address pools on separate

IP networks (or subnets) with a single gateway address. This is the

basic support for "secondary nets", e.g. a router that is acting as aBOOTP relay for an interface which has addresses for more than

one IP network or subnet.

Ability to configure groups of clients based upon client-supplieduser and/or vendor class. Note: this is a feature that might be used

to assign different client-groups on the same physical LAN to

different logical subnets. Administrator-settable T1/T2 lengths.


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Interaction with another DHCP server. Note that there are a

number of interactions that one might support and that a standard

set & method is in the works. Use of PING (ICMP Echo Request) to check an address prior to

dynamically allocating it.

Server grace period on lease times. Ability to force client(s) to get a new address rather than renew.

Following are some features related not to the functions that the server is

capable of carrying out, but to the way that it is administered.

Ability to import files listing manually allocated addresses (as

opposed to a system which requires you to type the entireconfiguration into its own input utility). Even better is the ability to

make the server do this via a command that can be used in a script,

rdist, rsh, etc.

Graphical administration. Central administration of multiple servers.

Ability to import data in the format of legacy configurations, e.g./etc/bootptab as used by the CMU BOOTP daemon.

Ability to make changes while the server is running and leases are

being tracked, i.e. add or take away addressees from a pool,modify parameters.

Ability to make global modifications to parameters, i.e., that apply

to all entries; or ability to make modifications to groups of ports or

pools. Maintenance of a lease audit trail, i.e. a log of the leases granted.

5. What freeware DHCP servers are available?

(This is not necessarily a complete list)

950415 Bootp server:Bootp 2.4.3 (not DHCP, but with the "DHCP patches"

mentionedbelow, can handle DHCP requests)ftp://ftp.mc.com/pub/bootp-2.4.3.tar.Z950425 Bootp server version 2.4.3 with "samba" DHCP patches(does manual allocation of IP addresses)http://www.sghms.ac.uk/~mpreston/bootp_dhcp.tar.Z(within http://www.sghms.ac.uk/~mpreston/tools.htm)

950706 "samba" DHCP patches for bootp server:(does manual allocation of IP addresses) ftp://nimbus.anu.edu.au:/pub/tridge/samba/contributed/DHCP.patch(note: I've heard that the patched server will crash if it

receivesone particular optional packet, the DHCP Release packet)

950711 Patched bootp server supporting DHCP-based"automatic" allocation:(gives addresses dynamically, but never takes them away)
ftp://ftp.mc.com/pub/bootp-2.4.3.tar.Zhttp://www.sghms.ac.uk/~mpreston/bootp_dhcp.tar.Zhttp://www.sghms.ac.uk/~mpreston/tools.htmftp://nimbus.anu.edu.au/pub/tridge/samba/contributed/DHCP.patchftp://nimbus.anu.edu.au/pub/tridge/samba/contributed/DHCP.patchftp://ftp.mc.com/pub/bootp-2.4.3.tar.Zhttp://www.sghms.ac.uk/~mpreston/bootp_dhcp.tar.Zhttp://www.sghms.ac.uk/~mpreston/tools.htmftp://nimbus.anu.edu.au/pub/tridge/samba/contributed/DHCP.patchftp://nimbus.anu.edu.au/pub/tridge/samba/contributed/DHCP.patch


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ftp://ftp.ntplx.net/pub/networking/bootp/bootp-DD2.4.3.tar.gz951219 BOOTP server and patches for DHCP ftp://africa.geomic.uni-oldenburg.de/pub/people/joey/dhcp/bootpd/960112 OS/2 port of BOOTP server with patches for manualDHCP support ftp://ftp.leo.org/pub/comp/os/os2/tcpip/systools/bootpd-243-dhcp.zip960130 Rose-Hulman Institute of Technology "Mondo-DB" LANadministrationproject: modified DHCP server plannedhttp://www.rose-hulman.edu/~allard/Mondo-DB/index.html950630 WIDE Project:mailto:[email protected] ProjectKeio Univ.Japanftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gz

Check Archie for dhcp-1.2.1 because lots of sites

distribute it.Beta version:ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gz960312 Carnegie Mellon University DHCP/BOOTP server (SunOS,dhcp-3.3.7)ftp://ftp.net.cmu.edu/pub/dhcp/dhcp-3.3.7.tar.gz961104 Princeton patches to CMU dhcpd 3.7.7.http://www.princeton.edu/~irwin/dhcpd.html971204 Internet Software Consortium (ISC) DHCP/BOOTP Serverhttp://www.isc.org/dhcp.html

6. What commercial DHCP servers are available?


951010 Wollongong: included in next release of PathWay forOpenVMS which is in

beta951219 Puzzle Systems: WEBserv (NLM(s) that do DHCP, BOOTP,HTTP, and FTP) mailto:[email protected] http://www.puzzle.com/951220 Process Software: server for OpenVMS included inTCPware for OpenVMS http://www.process.com/

960130 Digital: RoamAbout Mobile IP Client/Server NetworkSoftware V2.0 http://www.digital.com/info/Customer-Update/940620001.txt.html960312 Nevod Inc. Proxy IP/DHCP Server (PIP) Beta-1.0 http://www.nevod.com/pip/index.html960327 Xedia: IP/Assist 1.0 feature for their switchesincludes DHCP service. http://www.xedia.com/
ftp://ftp.ntplx.net/pub/networking/bootp/bootp-DD2.4.3.tar.gzftp://ftp.ntplx.net/pub/networking/bootp/bootp-DD2.4.3.tar.gzftp://africa.geomic.uni-oldenburg.de/pub/people/joey/dhcp/bootpd/ftp://africa.geomic.uni-oldenburg.de/pub/people/joey/dhcp/bootpd/ftp://ftp.leo.org/pub/comp/os/os2/tcpip/systools/bootpd-243-dhcp.zipftp://ftp.leo.org/pub/comp/os/os2/tcpip/systools/bootpd-243-dhcp.ziphttp://www.rose-hulman.edu/~allard/Mondo-DB/index.htmlmailto:[email protected]://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gzftp://ftp.net.cmu.edu/pub/dhcp/dhcp-3.3.7.tar.gzhttp://www.princeton.edu/~irwin/dhcpd.htmlhttp://www.isc.org/dhcp.htmlmailto:[email protected]://www.puzzle.com/http://www.process.com/http://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.nevod.com/pip/index.htmlhttp://www.xedia.com/ftp://ftp.ntplx.net/pub/networking/bootp/bootp-DD2.4.3.tar.gzftp://ftp.ntplx.net/pub/networking/bootp/bootp-DD2.4.3.tar.gzftp://africa.geomic.uni-oldenburg.de/pub/people/joey/dhcp/bootpd/ftp://africa.geomic.uni-oldenburg.de/pub/people/joey/dhcp/bootpd/ftp://ftp.leo.org/pub/comp/os/os2/tcpip/systools/bootpd-243-dhcp.zipftp://ftp.leo.org/pub/comp/os/os2/tcpip/systools/bootpd-243-dhcp.ziphttp://www.rose-hulman.edu/~allard/Mondo-DB/index.htmlmailto:[email protected]://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gzftp://ftp.net.cmu.edu/pub/dhcp/dhcp-3.3.7.tar.gzhttp://www.princeton.edu/~irwin/dhcpd.htmlhttp://www.isc.org/dhcp.htmlmailto:[email protected]://www.puzzle.com/http://www.process.com/http://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.nevod.com/pip/index.htmlhttp://www.xedia.com/


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960420 Competitive Automation's JOIN (415-321-4006):SunOS4.x, Solaris2.x,

Digital Unix 3.2, 4.x, HP-UX 9 & 10 DHCP/BOOTPservers. http://www.join.com/960514 SunSoft: Solstice SolarNet PC-Admin 1.5 includes aDHCP/BOOTP server. http://www.sun.com/solstice/Networking-products/PC-Admin.html960514 Microsoft: DHCP server included in Windows NT Server3.51 http://www.microsoft.com/NTServer/ http://www.microsoft.com/BackOffice/techbriefs/tech1000.htm ftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/tcpipimp.doc960514 ON Technology: IPTrack 1.0 is a Novell Server-basedDHCP/BOOTP server (NLM) http://www.on.com/on/onprods/iptrack.html/960514 FTP Software: OnNet Server 2.0 (Services OnNet

Product) http://www.ftp.com/mkt_info/services.html960531 Cisco: server in development. http://www.cisco.com/960620 Farallon: a DHCP server is built into its NetopiaInternet Router http://www.farallon.com/960716 Weird Solutions: BOOTP Server NT supports both BOOTPand statically

allocated DHCP. http://www.mhi.se/960808 Novell: NetWare/IP 2.2 (free upgrade to NetWareservers)

includes a DHCP/BOOTP server; unlike NetWare/IP 2.2itself, this

server will run on NetWare 3.12. ftp://ftp.novell.com/updates/unixconn/nwip22/nip22b.exe http://netware.novell.com/discover/nwip/index.htm960809 Silicon Graphics: 'proclaim' software for SGIworkstations; part

of IRIXpro. http://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.html http://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXprospecs.html960829 Isotro: NetID DHCP Server (BOOTP/DHCP server)

(No longer available from Isotro)960912 Cisco: (announced) DHCP/BOOTP server for Solaris,HP-UX, and

AIX, Windows NT (Alpha & Intel) included in Cisco'sDNS/DHCP

Manager V1.0 and Cisco's Server Suite 1000 V1.0 http://www.cisco.com/960917 SunSoft: (future) DHCP/BOOTP server to be bundledwith Solaris 2.6
http://www.join.com/http://www.sun.com/solstice/Networking-products/PC-Admin.htmlhttp://www.sun.com/solstice/Networking-products/PC-Admin.htmlhttp://www.microsoft.com/NTServer/http://www.microsoft.com/BackOffice/techbriefs/tech1000.htmhttp://www.microsoft.com/BackOffice/techbriefs/tech1000.htmftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/tcpipimp.docftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/tcpipimp.dochttp://www.on.com/on/onprods/iptrack.html/http://www.ftp.com/mkt_info/services.htmlhttp://www.cisco.com/http://www.farallon.com/http://www.mhi.se/ftp://ftp.novell.com/updates/unixconn/nwip22/nip22b.exeftp://ftp.novell.com/updates/unixconn/nwip22/nip22b.exehttp://netware.novell.com/discover/nwip/index.htmhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXprospecs.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXprospecs.htmlhttp://www.cisco.com/http://www.join.com/http://www.sun.com/solstice/Networking-products/PC-Admin.htmlhttp://www.sun.com/solstice/Networking-products/PC-Admin.htmlhttp://www.microsoft.com/NTServer/http://www.microsoft.com/BackOffice/techbriefs/tech1000.htmhttp://www.microsoft.com/BackOffice/techbriefs/tech1000.htmftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/tcpipimp.docftp://ftp.microsoft.com/bussys/winnt/winnt-docs/papers/tcpipimp.dochttp://www.on.com/on/onprods/iptrack.html/http://www.ftp.com/mkt_info/services.htmlhttp://www.cisco.com/http://www.farallon.com/http://www.mhi.se/ftp://ftp.novell.com/updates/unixconn/nwip22/nip22b.exeftp://ftp.novell.com/updates/unixconn/nwip22/nip22b.exehttp://netware.novell.com/discover/nwip/index.htmhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXprospecs.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXprospecs.htmlhttp://www.cisco.com/


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or as hte "Internet Server Supplement" to Solaris2.5.1. http://www.sun.com/961118 Network TeleSystems: Shadow (PC-based) also doesBOOTP http://www.nts.com/NTS/shadow.html961217 Hewlett-Packard: HP-UX 10.10 and subsequent versionsinclude a bootp

server with DHCP extensions.970325 American Internet Corp: Net Registrar (for WindowsNT and Solaris) http://www.american.com/970403 Microsoft: BOOTP/DHCP server in NT 4.0 SP2. http://www.microsoft.com/kb/articles/q161/5/71.htm970415 VICOM: VICOM DHCP Server (runs on Macintosh/MacOS) http://www.vicomtech.com/dhcp.main.html970415 Sonic Systems: Sonic DHCP Internet Server runs onMacintosh/MacOS,

also does BOOTP http://www.sonicsys.com/dhcp.html

970805 Process Software: MultiNet 3.5 for OpenVMS includesDHCP/BOOTP server. http://www.process.com/multinet/971217 Quadritek Systems, Inc.: QDHCP (NT or UNIX), alsodoes BOOTP http://www.quadritek.com/products/qipdhcpserv.html980518 Billiter Consultants: ipLease DHCP server (32bitWindows) http://www.billiter.com/980331 Deerfield Communications: DHCP server included inWingate

Pro (2.1b) "proxy server" http://www.wingate.net/980603 IBM OS/400 Version 3 Release 7 and subsequentversions includes

a DHCP/BOOTP server. http://www.as400.ibm.com/980611 Bay (Xylogics) Remote Annex (RA) and Remote AccessConcentrator

(RAC) communication servers have proxy DHCP clientsince release

13.2, December 1995. http://www.baynetworks.com/980612 IBM: DHCP server included in AIX 4.1.4 and beyond.Includes

BOOTP service. http://www.rs6000.ibm.com/

980612 IBM: TCP/IP Version 4.1 for OS/2 Warp includes DHCP,BOOTP and

DDNS and java-based administration. http://www.software.ibm.com/os/warp-server

7. What freeware DHCP clients are available?

http://www.sun.com/http://www.nts.com/NTS/shadow.htmlhttp://www.american.com/http://www.microsoft.com/kb/articles/q161/5/71.htmhttp://www.vicomtech.com/dhcp.main.htmlhttp://www.sonicsys.com/dhcp.htmlhttp://www.process.com/multinet/http://www.quadritek.com/products/qipdhcpserv.htmlhttp://www.billiter.com/http://www.wingate.net/http://www.as400.ibm.com/http://www.baynetworks.com/http://www.rs6000.ibm.com/http://www.software.ibm.com/os/warp-serverhttp://www.sun.com/http://www.nts.com/NTS/shadow.htmlhttp://www.american.com/http://www.microsoft.com/kb/articles/q161/5/71.htmhttp://www.vicomtech.com/dhcp.main.htmlhttp://www.sonicsys.com/dhcp.htmlhttp://www.process.com/multinet/http://www.quadritek.com/products/qipdhcpserv.htmlhttp://www.billiter.com/http://www.wingate.net/http://www.as400.ibm.com/http://www.baynetworks.com/http://www.rs6000.ibm.com/http://www.software.ibm.com/os/warp-server


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960809 WIDE Project includes a client for BSD and SunOSsystems: mailto:[email protected]

WIDE ProjectKeio Univ.Japan

ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gz

Check Archie for dhcp-1.2.1 because lots of sitesdistribute it.

Beta version: ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gz960904 Linux bootp client: bootpc; DHCP being added overtime. ftp://ftp.damtp.cam.ac.uk/pub/linux/bootpc/970415 dhcpcd (for Linux 1.2.xx, 1.3.xx, 2.0.x) ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/

version 0.4a:

ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.4a.tar.gz

version 0.5: ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5.tar.gz

version 0.5-p1: ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5-p1.tar.gz

version 0.6: ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.6.tar.gz971204 Internet Software Consortium (ISC) DHCP/BOOTP Server

Distribution includes a client. See ISC server insection above

on "Freeware Servers".

8. Which vendors of client software currently support DHCP?


950417 Shiva: proxy client for remote users (in Lanroversand Netmodems)950425 Hewlett-Packard950502 NetManage: Chameleon 4.5

950630 Beame & Whiteside Software: resells Dirk KoeppenEDV-Beratungs-GmbH's

TCP/IP BOOT-PROM950705 Microsoft: MS-TCP/IP 3.11a & MS-TCP/IP 3.11b950711 Microsoft: Windows NT 3.5950711 Microsoft: Windows for Workgroups 3.11a950711 Frontier Technologies(800-929-3054): in SuperTCP forWindows http:www.frontiertech.com
mailto:[email protected]://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gzftp://ftp.damtp.cam.ac.uk/pub/linux/bootpc/ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.4a.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.4a.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5-p1.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5-p1.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.6.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.6.tar.gzhttp://www.dhcp-handbook.com/dhcp_faq.html#wfdsahttp://www.frontiertech.com/mailto:[email protected]://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gzftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gzftp://ftp.damtp.cam.ac.uk/pub/linux/bootpc/ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.4a.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.4a.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5-p1.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.5-p1.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.6.tar.gzftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp/dhcpcd-0.6.tar.gzhttp://www.dhcp-handbook.com/dhcp_faq.html#wfdsahttp://www.frontiertech.com/


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[email protected] Beame & Whiteside(800-720-7151): BW-Connect NFS forDOS & Windows950802 Wollongong: PathWay Access ver 3.2 (Windows) http://www.twg.com/950802 WRQ: Reflection Network Series products (version 5)for Windows http://www.wrq.com/950814 Competitive Automation(415-321-4006): SunOS4.x,Solaris2.x and

DECOSF3.x,4.x clients950915 Stampede: included in Remote Office Gold951113 Persoft(800-368-5283): TCP Addition and Portable TCP http://www.persoft.com/951207 Dirk Koeppen EDV-Beratungs-GmbH: TCP/IP DHCP BootROMs (TCP/IP

BOOT-PROM) www.dunkel.de/dksoft951220 Attachmate: IRMA TCP Suite Version 3.1960130 Digital: RoamAbout Mobile IP Client/Server NetworkSoftware V2.0

http://www.digital.com/info/Customer-Update/940620001.txt.html960209 FTP Software: included in OnNet 2.0 (Windows) http://www.ftp.com/960209 FTP Software: PC/TCP 4.0 (DOS) http://www.ftp.com/960312 Core Systems: Internet-Connect for Windows 95Version 2.1 has DHCP

proxy client. http://ns1.win.net/~core/Coresys/homepage.html960313 Apple: Open Transport 1.1 included with System 7.5.3& runs on

68030, 68040, and PowerPC Macintoshes.960314 Apple: Open Transport 1.1 shrink wrap version willbe offered.960408 IBM: Client DHCP software for Windows 3.x.960408 IBM: Client DHCP software for MS/PC-DOS.960501 SunSoft: included in PC-NFS Pro 2.0 for Windows960501 NetManage: included in ChameleonNFS 4.6960503 FTP Software: included in OnNet32, Version 1.0(Windows 95 and NT) http://www.ftp.com/960514 Novell: Client32 for DOS/Windows 3.1 (beta) will useeither DHCP

or BOOTP to get IP parameters.960514 Novell: NetWare/IP for DOS, Windows 3.1, Windows 95,and

Windows NT uses DHCP to obtain IP parameters.960514 Novell: NetWare/IP servers can use DHCP to auto-configure their

IP parameters.960809 Silicon Graphics: included in IRIX since version 5.3. http://www.sgi.com/Products/software/IRIX6.2/IRIX62DS.html http://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.html960917 Sun: Solaris 2.6.
mailto:[email protected]://www.twg.com/http://www.wrq.com/http://www.persoft.com/http://www.dunkel.de/dksofthttp://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.ftp.com/http://www.ftp.com/http://ns1.win.net/~core/Coresys/homepage.htmlhttp://www.ftp.com/http://www.sgi.com/Products/software/IRIX6.2/IRIX62DS.htmlhttp://www.sgi.com/Products/software/IRIX6.2/IRIX62DS.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlmailto:[email protected]://www.twg.com/http://www.wrq.com/http://www.persoft.com/http://www.dunkel.de/dksofthttp://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.digital.com/info/Customer-Update/940620001.txt.htmlhttp://www.ftp.com/http://www.ftp.com/http://ns1.win.net/~core/Coresys/homepage.htmlhttp://www.ftp.com/http://www.sgi.com/Products/software/IRIX6.2/IRIX62DS.htmlhttp://www.sgi.com/Products/software/IRIX6.2/IRIX62DS.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.htmlhttp://www.sgi.com/Products/hardware/challenge/IRIXpro/IRIXpro.html


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http://www.sun.com/961118 Network TeleSystems TCP Pro 3.0 for Windows http://www.nts.com/NTS/tcp_pro.html970805 Cisco: DHCP & BOOTP for Windows 3.1 included inCisco TCP/IP

Suite 100 for Windows (formerly MultiNet forWindows) V2.0

For Windows 95, uses the native support. http://www.cisco.com/980331 Deerfield Communications: DHCP server included inWingate

Pro (2.1b) "proxy server" http://www.wingate.net/980611 IBM: OS/2 WARP Version 4 (Merlin) has DHCP clientcapability in the

basic package. http://www.software.ibm.com/os/warp-client980612 IBM's DOS/Windows LAN Services (for IBM PC-DOS,Microsoft

MS-DOS, and/or Microsoft Windows 3.x)

980612 IBM's line of NetworkStations are all DHCP clients(or BOOTP) http://www.as400.ibm.com/networkstation/980612 IBM: AIX 4.1.4 client and server packages include aDHCP client. http://www.rs6000.ibm.com/

9. What are the DHCP plans of major client-software vendors?

Apple MacOS

MacTCP's successor, Open Transport, supports DHCP. Open Transport 1.1 ships

with System 7.5 Update 2.0 (which updates MacOS to version 7.5.3, releasedMarch 11, 1996) and supports any 68030, 68040, or PowerPC Macintosh. A

shrink wrap version of Open Transport is planned.Microsoft Windows95

supports it and does not support BOOTP. I heard a rumor that BOOTP support

will be added.

Novell LAN Workplace for DOSFor supporting DOS/Windows 3.1, Client32 for DOS/Windows, due in June

1996, will provide the TCP/IP stack functions and will support DHCP and

BOOTP. For Windows 95 and Windows NT, the native stack will be used so thatDHCP is supported.

IBM OS/2 Warpsupports it.

10. What Routers forward DHCP requests?

(This is not necessarily a complete list).
http://www.sun.com/http://www.nts.com/NTS/tcp_pro.htmlhttp://www.cisco.com/http://www.wingate.net/http://www.software.ibm.com/os/warp-clienthttp://www.as400.ibm.com/networkstation/http://www.rs6000.ibm.com/http://www.sun.com/http://www.nts.com/NTS/tcp_pro.htmlhttp://www.cisco.com/http://www.wingate.net/http://www.software.ibm.com/os/warp-clienthttp://www.as400.ibm.com/networkstation/http://www.rs6000.ibm.com/


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Note that in general, these routers probably already had BOOTP

forwarding, but lacked the support for the BOOTP broadcast flag (see

"broadcast flag" under What are the Gotcha's? above). It is likely thatmany other routers also support BOOTP forwarding.

Cisco(from Cisco FAQ) Routers running GSYS version 9.21(4) and 10.0(3) as well as

later releases.Wellfleet/Bay

(from Wellfleet FAQ) DHCP is supported by enabling BOOTP support (with

transmission and/or reception as needed). Starting with version 9.00 of theirrouting software BayRs.

3Com Netbuilder

Version 7.2 software can support DHCP relaying through the use of its genericUDP Helper service. Version 8.0 and later officially supports DHCP.

Xyplex

Version 5.5 of their routing software supports DHCP.ALANTECThe switches' "router" function has have been handling BOOTP forwarding since

around 1993. Support for the broadcast flag introduced in a maintenance release

of 2.5 of their software and is in version 2.6 and later.IBM 2210

I've confirmed that Version 1 Release 2 has a BOOTP relay agent. I haven't found

out anything about support for the broadcast flag.ACC

Version 7.2 (about 1994) and later support DHCP relaying.

Proteon/Digital

I'm not sure what is the first version that has this support.Novell MPR

The same as for their server.

IBM 6611Supports BOOTP forwarding.

11. What Routers include DHCP servers?

DHCP requires disk storage (or some other form of reliable non-volatile

storage), making the task of DHCP service more compatible with serversthan with dedicated routers. The large-scale routers (i.e., those of Cisco,

Bay, Fore) don't an will probably never will have a DHCP server function.

But there are a number of types of servers that can be configured to route

and serve DHCP. This includes Novell servers and computers runningUnix. There are also units designed to handle two or more aspects of your

Internet connection, e.g. routing between a LAN and a leased line as well

as doing other functions to allow computers on the LAN to reach theInternet (or corporate intranet as the case may be). One example is
http://www.dhcp-handbook.com/dhcp_faq.html#watgxhttp://www.dhcp-handbook.com/dhcp_faq.html#watgxhttp://www.dhcp-handbook.com/dhcp_faq.html#watgxhttp://www.dhcp-handbook.com/dhcp_faq.html#watgx


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Farallon's Netopia Internet Router mentioned above under commercial

servers.

12. What Routers use DHCP to configure their IP addresses?

The DHCP RFC specifically says that DHCP is not intended for use inconfiguring routers. The reason is that in maintaining and troubleshooting

routers, it is important to know its exact configuration rather than leaving

that to be automatically done, and also that you do not want your router'soperation to depend upon the working of yet another server.

It may be possible to configure some types of more general-purpose

computers or servers to get their addresses from DHCP and to act as

routers. Also, there are remote access servers, often which are usually nottrue routers, which use DHCP to acquire addresses to hand out to their

clients.

13. What Servers forward DHCP requests?

Windows NT's 3.51 Service Pack 3 (and 4) includes a BOOTP (&DHCP) relay agent as part of "Multi Protocol Router". 3.51).

For Novell servers, there are NLMs that forward BOOTP requests,

thus DHCP requests. The "BOOTPFWD NLM" is included inNetWare 4.1. You can get this support in NetWare 3.11 and 3.12

also by applying the TCPN01.EXE patch which is located at

ftp://ftp.novell.com/updates/inet/mpr211/tcpn01.exe and on

Netwire. Two other such NLMs (possibly old versions of thesame) that are available online:

ftp://netlab2.usu.edu/misc/bootpfd.zip(unsupported Novellsoftware, 1993) ftp://netlab2.usu.edu/misc/bootp311.zip(unsupported

Novell software, 1991)

Also for Novell servers, the DHCP server that comes withNetWare/IP 2.2 can be configured to be just a BOOTP/DHCP

forwarding agent.

AIX, through its dhcprd daemon. Warp Server Version 4.

14. Which implementations support or require the broadcast flag?

The broadcast flag is an optional element of DHCP, but a client which sets

it works only with a server or relay that supports it.

Clients

Microsoft Windows NT
ftp://ftp.novell.com/updates/inet/mpr211/tcpn01.exeftp://netlab2.usu.edu/misc/bootpfd.zipftp://netlab2.usu.edu/misc/bootp311.zipftp://ftp.novell.com/updates/inet/mpr211/tcpn01.exeftp://netlab2.usu.edu/misc/bootpfd.zipftp://netlab2.usu.edu/misc/bootp311.zip


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DHCP client support added with version 3.5 sets the broadcast flag. Version 3.51

and later no longer set it. The exception is in the remote access support: it sets the

flag when it uses DHCP to acquire addresses to hand out to its PPP clients.tcp/ip-32 for Microsoft Windows for Workgroups (WFW)

Version 3.11a sets it, but version 3.11B doesn't.

Microsoft Windows 95Does not set the broadcast flag.

15. What servers support secondary subnet numbers?

(These are not complete lists) The following servers can handle dynamic

allocation on secondary subnet numbers:

IPTrack version 2.0 ISC

JOIN

SGI's DHCP Server under IRIX 6.2 Cisco (previously TGV)

NetID

Microsoft Windows NT 4.0 (since service pack 2)

Sonic QDHCP

ipLease

IBM Warp Server Version 4 IBM AIX

The following can serve manually allocated addresses on secondary

subnet numbers:

IPTrack version 2.0 ISC

JOIN

QDHCP

The following cannot support secondary subnet numbers:

Microsoft Windows NT 3.51 and 4.0 (through RC1) WIDE

Sonic DHCP Server16. What servers support RFC-based dynamic DNS update?

The following DHCP servers include the ability to make use of the RFC2136/2137 DNS feature to make dynamic updates to the DNS. To make

use of this ability, you need a DNS server that supports this feature. A

likely use is to create temporary DNS records that associate a fullyqualified DNS name derived from the client's netbios name with the


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client's leased IP number. Another use might be to associate DNS names

with MAC addresses. These products might support one or both of these

uses.

American Internet Corp Net Registrar

QDHCP IBM's Warp Server (version 4 and after)

IBM's AIX server (version 4.1 and after)17. How can I run Windows 95 without a DHCP server?

Not really a DHCP question, but it has been asked a lot, particularly by

sites for which changing from BOOTP represents a lot of work. Some

choices:

Use no server at all for the Windows 95 clients: set the addresses

in each client's setup.

Install a non-Microsoft TCP/IP stack for Windows 95 that supportsBOOTP.

Switch from your current BOOTP server to one that supports both

BOOTP and DHCP.

The 'billgPC' program uses BOOTP (instead of DHCP) toconfigure Windows 95's native IP stack:

http://www.panix.com/~perin/ (note: it also works with Windows

NT).

A Document that addresses this question is the Windows 95tm Networking FAQ, http://www-

leland.stanford.edu/~llurch/win95netbugs/faq.html

18. Do any servers limit the MAC addresses that may roam? IBM's AIX and OS/2 WARP DHCP servers.

ISC.

19. What analyzers decode DHCP?

Release 5.0 of Network General Corporation's Sniffer software. I believe one of the free Unix implementations has included in its

distribution a program that captures and decodes BOOTP and

DHCP negotiations. Microsoft's SMS includes a protocol analyzer called "Network

Monitor" that decodes DHCP. All NT software includes a remote

agent for it. NetXRay, software that runs under Windows NT adn 95.

http://ngcwebgate.ngc.com/product_info/netxray/netxray.html

PacketView (LAN), SerialView (PPP and SLIP), and ISDNView

(PPP over ISDN) all are DOS programs that fully decode DHCPpackets. href="http://www.klos.com/

20. What administration tools administer DHCP configurations?
http://www.panix.com/~perin/http://www-leland.stanford.edu/~llurch/win95netbugs/faq.htmlhttp://www-leland.stanford.edu/~llurch/win95netbugs/faq.htmlhttp://www-leland.stanford.edu/~llurch/win95netbugs/faq.htmlhttp://ngcwebgate.ngc.com/product_info/netxray/netxray.htmlhttp://www.klos.com/http://www.panix.com/~perin/http://www-leland.stanford.edu/~llurch/win95netbugs/faq.htmlhttp://www-leland.stanford.edu/~llurch/win95netbugs/faq.htmlhttp://ngcwebgate.ngc.com/product_info/netxray/netxray.htmlhttp://www.klos.com/


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Quadritek's QIP network administration product includes an

interface to Competitive Automation's JOIN DHCP server and

IBM's DHCP server and their own server.21. How do I make a client give up its lease?

This is a general question, but the answer is of necessity specific to theclient-implementation. Naturally, one way to avoid the problem is to keep

leases short enough that you are not obliged to do this.

One method mentioned is to temporarily change the clock on the

client.

For a Win95 client, the winipcfg.exe program can do it.

22. What are the Gotcha's specific to various implementations?

In many cases, new releases have solved the problems that have been

identified with various DHCP implementations.

An extra server feature is required to handle the allocation of

addresses on the secondary IP addresses associated with a routerport. You may find out after the fact that you have such secondary

addresses

There have been servers that are inflexible as to the list ofconfiguration parameters they were able to serve. If your client

requires certain parameters, you could find such a server unusable.

I hate to cast wide suspicions, but I've heard occasional word on

client DHCP implementations that do not implement the entireprotocol. Doing so requires that the software module be able to

wake up again after a specified period of time and "renew thelease", i.e., ask to continue using the IP number. This is at least onefeature of DHCP that is very hard to implement in some simpler

systems.

A specific complaint about Microsoft's Windows 95 dhcp client: ittimes out its requests much more quickly than the times specified

by RFC1541 section 4.1. Among the circumstances that can turn

this into a practical problem are the latencies due to relay agentsand a server's use of ICMP echo to doublecheck the address. While

it works with Microsoft's own NT-based server, the problem

prevents interoperation with some other DHCP servers under some

conditions. Microsoft is rumored to have developed an updaternamed VDHCPUPD.EXE to patch this problem, once available

through the following patch: File: Vdhcp.386

File Last Modified Date: 02/12/96

File Size: 27,985 bytes

File Version Information: 4.00.951
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It consists of 2 files, vdhcpupd.exe and vdhcpupd.txt. I've since

been told that a newer version is 4.00.954. I've also been told that

the exe file is on the net athttp://www.halcyon.com/cerelli/software/vdhcpupd.exe

There are a number of issues regarding the patched bootp servers.These have been reported to re DD2.4.3:

'When run from inetd, I had problems with "Could not bindport" and DHCP request failure. I don't know why, and the

problem went away when bootpd is run as a daemon.'

'Unless you set "dl" to some value in the bootptab file, theDHCP lease time, renewal time and prebinding time will be

rubbish, which will cause occasional renewal problems.'

One symptom you might see is Microsoft DHCPimplementations using 5-minute leases, which is their

default. Other implementations may not run at all.

Early Microsoft DHCP client implementations required thebroadcast bit. Current ones do not. I have heard a vague complaints about the Microsoft

implementations of DHCP: that it does not follow the standards. I

could use details. Early Apple Open Transport implementations did not always fill

out packets to BOOTP's 300-byte minimum, thus BOOTP

forwarding agents that follow the BOOTP RFC and discard suchpackets end up discarding such DHCP packets, causing some of

the functions to fail. Open Transport 1.1 fixes this.

Pre 1.1 versions of Open Transport experienced interoperability

problems with the Microsoft NT DHCP server. The very first announced release of Carnegie Mellon's server,

dhcp-3.3.6, circa March 1996 has shown signs of needing to be

shaken out to be more easily compiled outside of its developmentenvironment.

Windows NT server v3.51 allows the administrator to specify

addresses within its assignment range to be excluded, but does notalways exclude them.

Report: Novell's NetwareIP 2.2 server refuses to hand out dynamic

bootp assignments to hosts mentioned in the local /etc/hosts file,even if configured to do so.

I've heard a report that some combinations of versions of Unix &

the ISC server will transmit packets to the subnet broadcast address

rather than the default broadcast address (255.255.255.255), whichimpedes interoperability with some clients.

Windows 95 DHCP client answers pings from an IP address even

after the the client's lease has expired. Thus a server that uses pingto check to see that an IP number is unused before reassigning it

may find that it is still in use.
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Windows 95 DHCP client cannot handle a lease renewal offered

by a different server.

Some clients have no way to configure a class option, which canbe a showstopper if you need to use the class option to help decide

what pool of addresses the client uses.

I've heard reports that Windows 95, or at least some versions willuse an address after the lease has expired under some

circumstances, even when renewal requests have been turned

down. With properly behaving clients, an IP administrator cansafely make the following statement: "As long as all the clients are

set to get their addresses through DHCP, I can tell which addresses

are not being used by the clients simply by checking the server to

see which IP addresses have no outstanding leases." The reportssuggest that Windows 95 implementations won't allow this

statement to be assumed.

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