DELL SOLUTION STATION

Tuesday, November 20, 2007

DHCP NOTES

· What is DHCP?
· DHCP stands for "Dynamic Host Configuration Protocol".
· 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 most significant piece of information distributed in this manner is the IP address.
· 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 network addresses.
· Who Created It? How Was It Created?
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 is recorded 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)
· 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't support other parameters and using it, a server can only serve a single LAN. DHCP and BOOTP are designed so they can be routed.
· 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 in common (easing moves of networked computers), VLANs represent a more revolutionary change to a LAN than DHCP. A DHCP server and forwarding 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 be given 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 (as well 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 IP address 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 the client is moved to.
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 VLANs requires 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 are being 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 the same 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 already configured, which precludes the use of network to get the configuration information from a DHCP or BOOTP server.
· What protocol and port does DHCP use?
DHCP, like BOOTP runs over UDP, utilizing ports 67 and 68.
· 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.
· 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.
· 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.
· 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.
· 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 be configured to do this for IP. However, this method of IP address assignment has disadvantages.
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.
A network might be temporarily divided into two non-communicating networks while a network component is not functioning. During this time, two different client-machines might end up claiming the same IP number. When the network comes back, they start malfunctioning.
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 lead both 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.
· 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.
· 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".
· Can a BOOTP client boot from a DHCP server?
Only if the DHCP server is specifically written to also handle BOOTP queries.
· 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.
· 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 goals for 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.
· 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 the BOOTP server is acceptable to the DHCP client." (section 3). The word "MAY" indicates such support, however useful, is left as an option.
· 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 updated dynamically. 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 and DHCP servers that accomplish this through proprietary means.
· 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 from the other server.
However, without communication between the two servers to share their information on current leases, when one server is down, any client with a lease 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 this issue with their own proprietary server-to-server communication.
· 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".
· Is there a DHCP mailing list?
There are several:
List Purpose
dhcp-v4@bucknell.edu General discussion: a good list for server administrators.
dhcp-bake@bucknell.edu DHCP bakeoffs
dhcp-impl@bucknell.edu Implementations
dhcp-serve@bucknell.edu Server to server protocol
dhcp-dns@bucknell.edu DNS-DHCP issues
dhcp-v6@bucknell.edu DHCP for IPv6

The lists are run by listserv@bucknell.edu which can be used to subscribe and sign off. Archives for the dhcp-v4 list (which used to be called the host-conf list) are stored at ftp://ftp.bucknell.edu/pub/dhcp/.
· 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.
· 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 the same 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 single interface. 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:
Dynamic allocation supported on secondary subnet numbers on the LAN to which the server is attached.
Dynamic allocation supported on secondary subnet numbers 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 server must 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 of these cases, but not all of them. See section below listing the capabilities of some servers.
· If a physical LAN has more than one logical subnet, how can different groups of clients be allocated addresses on different subnets?
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 class option to be preconfigured and the server software must support its use to control which pool a client's address is allocated from.
· Where is DHCP defined?
§ In Internet RFCs.
RFC 2131
R. 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 2132
S. 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
· 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 other parameters. Such a communications server may support the use of DHCP to acquire the IP addresses it gives out. This is sometimes called doing DHCP 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 an IP 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 IP address, but many communications servers support non-standard ways of doing 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 device without 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 use something 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 MAC address, 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 to use a different "client ID type" for your hardware address. Client ID type 1 means you're using MAC addresses. However, client ID type 0 means an ASCII string.
· Can a client have a home address and still float?
There is nothing in the protocol to keep a client that already has a leased or 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.
· 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.
· 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 to support 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:
§ Find a server that is administered like your BOOTP server only that also serves DHCP. For example, one popular BOOTP server, the CMU server, has been patched so that it will answer DHCP queries.
§ Run both a DHCP and a BOOTP server. It would be good if I could find out the gotcha's of such a setup.
§ Adapt your site's administration to one of the available DHCP/BOOTP servers.
§ 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-BOOTP clients at your site.
· 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 be designed to implement such a requirement, presumably as an option to the server administrator. See section below on servers that implement this.
· Is there an SNMP MIB for DHCP?
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.
· 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 a connecting Windows 95 computer, with the intention of giving it an IP number during its connection process.
· 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 DHCP server.
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, the client 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 new leases, 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 client configuration 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 of 15 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 some particular 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 lines over which the DHCP packets will be run?
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 to watch 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 is avoided.
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 clients are 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 to them 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 permanent addresses. 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 as long 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 minutes
To 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 days
Long enough that a weekend server outage that gets fixed on Monday will not result in leases terminating.
4 months
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 year
If 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.
· 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 extra work.
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.
· 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 out nor can it distinguish between a computer's permanent MAC address and one set by the computer's user. DHCP can impose no restrictions on what IP address can use a particular port nor control the IP address used by any client.
· 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" nodes ending 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 via tftp being directed to a different file (possibly on a different server), thus allowing the perpetrator to take over the client. 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 IP address 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 practical terms, 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 on for 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 the subnet 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 has multiple network (or subnet) numbers. When the router is relaying requests from such a LAN to the DHCP server, it must pass along as 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 handle such 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 for identifying 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 such methods. 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 moved around (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 the home site and receives an address from one of the two serves. 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 for the 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 that holds 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 on the 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 consume more 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 being used 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 use DHCP.
§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: one workaround is to fool with the client computer's clock).
B. Info on Implementations
· What features or restrictions can a DHCP server have?
While the DHCP server protocol is designed to support dynamic management 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:
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 a configuration 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's administrator 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 dynamic addresses.
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 allocated dynamically. 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 a BOOTP relay for an interface which has addresses for more than one IP network or subnet.
§ Ability to configure groups of clients based upon client-supplied user 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.
§ 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 entire configuration 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

Relevant Questions for CUSTOMERS !

Questions to ask the Customer:
1. When did the Problem Begin?
2. What Operating System and Service Packs are installed?
3. Does it work in Safe Mode or DOS?
4. Does the problem only occur in a specific program?
5. Has the problem occurred before?
6. Is the system attached to a network? What Type?
7. If Win9x or Win2k how do affected devices look in device manager?
8. Has any Hardware or Software been added to the system?
9. What BIOS revision are you running? (have you checked BIOS settings, Flashed BIOS)
10. Have we eliminated CRU’s - (Reseat, Swap, Clean contacts on memory/drives)
11. Have the Diagnostics been run (specific like 3com, HDD90/90 or Dell Diags)
12. How long has the system been running? (could the problem be heat related)
13. Can the problem be reproduced? (Try to reproduce the problem)
These questions are commonly used to narrow the scope of the problem. All 13 are not necessarily applicable in every scenario. Using them relevantly will enhance call control and customer experience by: not making the customer repeat questions up front then have to re-answer them when the decision tree asks again in the detailed troubleshooting and keep the customer’s confidence that you are in control. Some questions are irrelevant depending on the particular problem the customer is having. The following examples show times in which particular questions are totally irrelevant:

· “Does it work in Safe Mode or DOS?” Would not be a relevant question if the problem that the customer is experiencing is a no power issue.
· “Does the problem occur in a specific program?” Is not a relevant question if the system is not booting to the Operating System.
· “What BIOS rev are you running?” Would be irrelevant if the system is experiencing no video on any output.
· “What Operating System and Service Packs are installed?” Would be irrelevant if the customer’s problem is the system won’t boot to the CD-Rom drive.
· “Is the system attached to a network?” Isn’t relevant when the customer issue is getting memory errors just after POST.
· “Does the problem occur in a specific program?” Would be irrelevant if the customer is calling for assistance in installing the OS.
· “How long has the system been running?” Is not a relevant question if the customer is experiencing a No POST?

Be aware to carry these steps into DSN so that you don’t ask repetitive questions once inside a DT that you have already established through earlier investigation. Such as:

“Is the system attached to a network?” and the answer is no. Then once you have gotten into a detailed DT it may ask to remove the system from a network. Through your earlier questions this would not be unnecessary and asking the customer to do this will cause the customers experience to be negatively affected, and could also lose the customer confidence in you.

These are only a few examples of situations where all 13 questions may not be relevant there maybe many more instances in which you will need to determine which question may or may not be relevant. In doing this you will be able to keep the call time to a minimum, get better details on the specifics of the customer’s problem, and provide a better customer experience.

Wednesday, November 07, 2007

Networking Protocols

The IP addresses are of two types:

Static IP Address

Dynamic IP Address

DHCP server layout

Static IP Address - Address that is obtained manually. The user / supervisor of the system / network assigns this address. This IP adress is not variable address relatively stays the same at each login to the network.

Dynamic IP Address - An address that is obtained from an entity called DHCP Dynamic Host Configuration Protocol server which provides the system loging onto the network with an IP address. This IP address may be variable from each instance of login of the system into the network.

APIPA - (Automatic Private IP Addressing) 169.254.X.X where X is any number from 1 to 254
In case the network does not have a DHCP server , the OS automatically assigns the system with an IP Address. This IP address cannot be used to connect to the internet. This is a Dynamic IP Address

IP Addressing Structures

IP Address Structure : aaa.bbb.ccc.ddd

where :

aaa.bbb is the Network Part of the IP Address
ccc.ddd is the Host Part of the IP Address

NETWORKING

PAN
LAN
WAN
MAN

Network Topology is segregated in to the following types:

Star Topology

_________________________________________________

Bus Topology

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Mesh Topology

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Ring Topology

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These connections are established with either Router Hub or a Switch

HUB - A non-intelligent device that broadcasts the data to all the systems in the network regardless of which system had generated the request.

SWITCH - An Intelligent device, which unicasts the data to specific devices which requested. Switch recognized the systems with the help of a MAC Id which is the unique ID given to the NIC devices. MAC is an acronym for Media Access Controller.MAC is a 12 digit Hexa-decimal Character set which is unique to each of the devices and would be assigned a port number which is responsible to channelize the data transfer to specific systems.

Windows XP Registry

Description of the Registry

The Microsoft Computer Dictionary, Fifth Edition, defines the registry as:

A central hierarchical database used in Microsoft Windows 98, Windows CE, Windows NT, and Windows 2000 used to store information that is necessary to configure the system for one or more users, applications and hardware devices.

The Registry contains information that Windows continually references during operation, such as profiles for each user, the applications installed on the computer and the types of documents that each can create, property sheet settings for folders and application icons, what hardware exists on the system, and the ports that are being used.

The Registry replaces most of the text-based .ini files that are used in Windows 3.x and MS-DOS configuration files, such as the Autoexec.bat and Config.sys. Although the Registry is common to several Windows operating systems, there are some differences among them.

A registry hive is a group of keys, subkeys, and values in the registry that has a set of supporting files that contain backups of its data. The supporting files for all hives except HKEY_CURRENT_USER are in the %SystemRoot%\System32\Config folder on Windows NT 4.0, Windows 2000, Windows XP, Windows Server 2003, and Windows Vista.

The supporting files for HKEY_CURRENT_USER are in the %SystemRoot%\Profiles\Username folder. The file name extensions of the files in these folders indicate the type of data that they contain. Also, the lack of an extension may sometimes indicate the type of data that they contain.

Registry hive Supporting files

HKEY_LOCAL_MACHINE\SAM Sam, Sam.log, Sam.sav

HKEY_LOCAL_MACHINE\Security Security, Security.log, Security.sav

HKEY_LOCAL_MACHINE\Software Software, Software.log, Software.sav

HKEY_LOCAL_MACHINE\System System, System.alt, System.log, System.sav

HKEY_CURRENT_CONFIG System, System.alt, System.log, System.sav, Ntuser.dat, Ntuser.dat.log,

HKEY_USERS\DEFAULT Default, Default.log, Default.sav

In Windows 98, the registry files are named User.dat and System.dat. In Windows Millennium Edition, the registry files are named Classes.dat, User.dat, and System.dat.Note Security features in Windows NT, Windows 2000, Windows XP, Windows Server 2003, and Windows Vista let an administrator control access to registry keys.The following table lists the predefined keys that are used by the system. The maximum size of a key name is 255 characters.

HKEY_CURRENT_USER
Contains the root of the configuration information for the user who is currently logged on. The user's folders, screen colors, and Control Panel settings are stored here. This information is associated with the user's profile. This key is sometimes abbreviated as "HKCU."

HKEY_USERS
Contains all the actively loaded user profiles on the computer. HKEY_CURRENT_USER is a subkey of HKEY_USERS. HKEY_USERS is sometimes abbreviated as "HKU."

HKEY_LOCAL_MACHINE
Contains configuration information particular to the computer (for any user). This key is sometimes abbreviated as "HKLM."

HKEY_CLASSES_ROOT
Is a subkey of HKEY_LOCAL_MACHINE\Software. The information that is stored here makes sure that the correct program opens when you open a file by using Windows Explorer. This key is sometimes abbreviated as "HKCR." Starting with Windows 2000, this information is stored under both the HKEY_LOCAL_MACHINE and HKEY_CURRENT_USER keys. The HKEY_LOCAL_MACHINE\Software\Classes key contains default settings that can apply to all users on the local computer. The HKEY_CURRENT_USER\Software\Classes key contains settings that override the default settings and apply only to the interactive user. The HKEY_CLASSES_ROOT key provides a view of the registry that merges the information from these two sources. HKEY_CLASSES_ROOT also provides this merged view for programs that are designed for earlier versions of Windows. To change the settings for the interactive user, changes must be made under HKEY_CURRENT_USER\Software\Classes instead of under HKEY_CLASSES_ROOT. To change the default settings, changes must be made under HKEY_LOCAL_MACHINE\Software\Classes. If you write keys to a key under HKEY_CLASSES_ROOT, the system stores the information under HKEY_LOCAL_MACHINE\Software\Classes. If you write values to a key under HKEY_CLASSES_ROOT, and the key already exists under HKEY_CURRENT_USER\Software\Classes, the system will store the information there instead of under HKEY_LOCAL_MACHINE\Software\Classes.

HKEY_CURRENT_CONFIG
Contains information about the hardware profile that is used by the local computer at system startup.

Tuesday, November 06, 2007

Audit Form

Handling Customer Objections to Fee Based Support

Isn't this included in the price of the computer? I bought a 3-year warranty…

The standard warranty covers hardware issues that occur on your system, and to keep your operating system functional. Any 3rd party software or peripheral issue requires additional coverage.

I'm willing to pay, but I don't want to be transferred - why can't you help me?

Well this is really an issue of specialized knowledge. I am personally trained in hardware issues, but we have other people who focus on software, virus removal, networking, and so on… there is a lot to know, so it's pretty difficult for one person to do it all.

I bought this part from Dell (E&A) why won't Dell support it?

Dell sells products from many vendors through Software and Peripherals. Dell does not manufacture or install these items. We do not have the technical specifications for this item. I can give you a list of support options including Dell on Call service which can help you with this product.

The last technician helped me with this issue, why won't you?

The last technician may have had specialized knowledge about that product. In general, Dell technicians are experts in troubleshooting Dell hardware. We do not have specific product knowledge or troubleshooting information about other vendor's products. I wouldn't want to make the issue worse by working with hardware that I'm not familiar with.
Dell has a service called Dell on Call, which can assist customers with many issues that are not covered by the Dell hardware warranty. Customers has been asking for a service like this and it's now available.

Why can't you give me more details about how much Dell on Call costs?

Dell often runs specials on the price, so it's difficult for me to say, but I believe the price is $69 for one-incident. There are also multi-incident packages available. I can transfer you to a Dell on Call representative who can tell you the current price and explain the offering in more detail to you."

What if the Dell on Call technician can't fix my issue?

Dell on Call technicians want to make sure that you're completely satisfied with the resolution that they provide. They'll even ask you at the end of the call if you're satisfied with the resolution. Dell on Call is backed by a total Satisfaction Guarantee, and you can request a refund if not satisfied.

Products Supported by Dell-On-Call

Spyware and Virus

Get rid of annoying pop ups.
Improve the performance of your computer.
Activate parental control features.
Arrange your Internet security to block pop ups.

Dell™ Products "How To Usage"

Desktop Computers
Notebook Computers
Modems
CD/DVD Drives
Video Cards
CD/DVD Writers
USB Memory
Key Data Backup
3rd Party Products

"Installation, Setup and Downloading Pictures"

Digital Camera connected to Dell PC
Printers connected to Dell PC
Optical Mouse Wireless Keyboard and Mouse

Office/Home Networking* Setup and Troubleshooting

Wireless Router Setup
Router setup (wired)
Printer Setup

*An office/home network setup is defined as connectivity of two Dell PC's and one printer.

Operating Systems Support

Help installing, upgrading and setting up XP operating systems not purchased with your Dell PC.
Help with maintenance and "how to" support
RE-installations as needed to resolve Spyware or Virus issues

Software Application Installation and basic "How To" usage

MS Word
MS Works
MS Excel
MS Access
MS Publisher
MS PowerPoint
MS Project
MS Visio
MS Front Page
Adobe Acrobat Reader
Windows Media Player
Roxio Easy CD Creator
Windows XP -
My Music
Dell Jukebox

Internet Access and Email Support

E-Mail Service setup/tutorial
Netscape Navigator
MS Internet Explorer
MS Outlook
MS Outlook Express

Software Installation

Dell On Call can assist you with the basic installation of most 3rd party software.

Items Not Supported by Dell On Call

Dell Hardware Repair or Replacement
Servers and non-home Network Operating Systems
Systems Operated by Windows 2000 and older
Other Manufacturer PC's

What Does "Dell on Call" Support ?

Dell on Call is designed to assist customers with hardware and software support issues that are outside the scope of standard Dell hardware support.
Since the amount of 3rd party products and support issues is huge, neither Dell nor Dell on Call could possibly support them all. The Dell on Call scope of support is anything that is outside the scope of the standard hardware warranty contract, with the following exceptions:

The following items are NOT support by Dell on Call:

Non-Windows operating systems and Microsoft server based operating systems
Home made software or drivers
Pre-Windows 98 operating systems
Data recovery
Database centric troubleshooting or database design
Advanced networking issues
Server Operating Systems
Password recovery
Programming
Issues covered by the standard Dell hardware warranty
Group Policy editor
Bypassing copyright protection
Dell customers with Gold Technical Support (except for company numbers 04 & 12...Dell on Call will support these customers)

Microsoft Windows XP Features

Microsoft Windows XP (XPerience) Operating System

Designed to deliver increased reliability, security, and performance compared to Windows 98SE, Microsoft® Windows® XP Professional is the ultimate Microsoft operating system for your Dell™ PC. It can help boost your productivity, protect your data, get you connected and speed you through whatever you're doing. Because there's never been a better time to Go Pro.

Get Connected, Stay Connected.
Microsoft Windows XP Professional lets you work or play where you're most comfortable. Effortlessly connect to your school's network from the dorm, classroom or off-campus hangout.

Keep Your Schoolwork Secure.
Windows XP Professional helps ensure that valuable research papers, exams and personal documents are safe from system failure and data theft, and helps protect private information while in transit over the Internet.

Work Smarter, Not Harder.
Windows XP Professional is designed to deliver enhanced reliability, increased performance and a more user-friendly interface compared to Windows 98SE. So you can be more productive, no matter what you're working on.

Make The Most Of Digital Media.
Windows XP Professional is an open door to the joys of digital media. It's built to make the most of today's powerful applications for digital music, photography, digital movies and gaming.

Take Mobile Computing Further.
Windows XP Professional is the ultimate operating system for your Dell™ notebook. From Wi-Fi connectivity to battery enhancements, it's designed to help you accomplish as much on the road as you do at home.

What are the new EFS features in Windows XP?

Microsoft Windows 2000 introduced the capability for data recovery with the implementation of Encrypting File System (EFS), and this capability has been enhanced in Windows XP. Microsoft Windows XP provides many enhancements in the area of data protection - especially Encrypting File System (EFS). Windows XP provides significant advancements in data recovery and protection, and private key recovery.
This article provides a technical walkthrough that illustrates how to use important data recovery and protection features in Windows XP. Also included are best practices and the steps you need to take to build an effective data recovery and protection strategy.
In addition to explaining strategies for data recovery and data protection in Windows XP, this article includes many step-by-step examples that illustrate how to set up the data recovery and data protection features you'll want to use when deploying a Windows XP data recovery and protection solution.
Note: EFS is only available on Windows XP Professional; it is not supported on Windows XP Home Edition.
The increased functionality of EFS has significantly enhanced the power of the Windows XP Professional client. Windows XP Professional now provides additional flexibility for corporate users when deploying security solutions based on encrypted data files and folders. These new features include:

Full support for revocation checking on certificates used by the system

Alternate color support (green) for encrypted files

Support for encrypted offline folders

Multi-user support for encrypted files in the shell user interface (UI)

Support for the Microsoft-enhanced cryptographic service provider (CSP)

Additional support for FIPS 140-1 Level 1 compliant symmetric algorithms (3DES [Data Encryption Standard])

End-to-end encryption using EFS over WebDAV

Enhanced recovery policy flexibility

Additional security features for protecting EFS data.

Wednesday, October 31, 2007