Abstract:
One embodiment of the present invention provides a system for looking up location-specific configuration information for a network node or a subnet. During system operation, a network node creates a query message containing a key that comprises an Internet Protocol (IP) prefix and a string, wherein the IP prefix identifies the network node or the subnet, and the string specifies the type of configuration information. The network node then sends the query message to a name server, which is part of a distributed system that provides a global naming service, wherein the name server additionally stores configuration information. Finally, the network node receives a response message from the name server, wherein the response message contains the requested configuration information.

Description:
RELATED APPLICATION 
       [0001]    The present patent is a continuation of, and hereby claims priority under 35 U.S. §120 to, pending U.S. patent application Ser. No. 10/877,401, entitled “Method and Apparatus for Looking up Configuration Information for a Network Node,” by inventor Stuart D. Cheshire, filed on 25 Jun. 2004 (Attorney Docket No. APL-P3398). 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the process of looking up configuration information for a network node. More specifically, the present invention relates to the process of looking up configuration information for a network node by sending a query message to a name server, which is part of a distributed system that provides a global naming service. 
         [0004]    2. Related Art 
         [0005]    The Internet is permeating more and more aspects of our lives—from buying cameras to buying real estate, and from reading a newspaper to watching a movie. 
         [0006]    Due to the Internet&#39;s complexity, a network node, such as a computer, that wants to participate in the Internet needs to lookup a large amount of configuration information. For example, a network node typically needs to look up the name of an e-mail server, before it can send or receive e-mail. 
         [0007]    The configuration information that a network node needs to lookup tends to be location specific. For example, the name of an e-mail server for a network node in an organization can be different from the name of an e-mail server for another network node within the same organization. Furthermore, it is cumbersome to ask the user to lookup the configuration information. Hence, there is a strong need for a mechanism that allows a network node to automatically lookup configuration information on its own. 
         [0008]    DHCP (Dynamic Host Configuration Protocol) is a commonly-used protocol that was designed to automatically assign IP addresses to network nodes. It has subsequently been extended to allow a network node to lookup configuration information. Today, many network nodes use DHCP for looking up configuration information. 
         [0009]    Unfortunately, there are many drawbacks in using DHCP for looking up configuration information. Since DHCP is typically used only once during system boot, the network node gets only one chance to lookup configuration information. This is a severe limitation, because it forces the network node to guess what kind of configuration information it is going to need in the future. For example, if the network node does not lookup the NetBIOS (Network Basic Input Output System) name server during system boot, the network node may not be able to provide this information to an application that requires this information during normal system operation, thereby preventing the application from running properly. 
         [0010]    Furthermore, since configuration information can change over time, the configuration information that was obtained using DHCP during system boot can be out of date. 
         [0011]    Note that, although it is possible to use DHCP to lookup configuration information during normal system operation, such lookup operations may not be supported by all DHCP servers. Moreover, performing a lookup during normal system operation may cause the DHCP server to assign a new IP address to the network node, which can cause many applications to malfunction. 
         [0012]    Furthermore, DHCP can only support up to 255 types of configuration information, which places a hard limit on the types of configuration information that can be looked up using DHCP. 
         [0013]    In addition, one of the benefits of IPv6 is that it allows a network node to configure IPv6 addresses for its interfaces without requiring a DHCP server. This is beneficial because it reduces the burden on network operators by reducing the number of servers they need to maintain. However, if network operators have to continue using DHCP servers even after upgrading to IPv6, one of the important advantages of using IPv6 will be eliminated. 
         [0014]    Hence, what is needed is a method and apparatus for looking up a wide range of location-specific configuration information for a network node, wherein the method and apparatus does not have the drawbacks described above. 
       SUMMARY 
       [0015]    One embodiment of the present invention provides a system for looking up location-specific configuration information for a network node or a subnet. During system operation, a network node creates a query message containing a key that comprises an Internet Protocol (IP) prefix and a string, wherein the IP prefix identifies the network node or the subnet, and the string specifies the type of configuration information. The network node then sends the query message to a name server, which is part of a distributed system that provides a global naming service, wherein the name server additionally stores configuration information. Finally, the network node receives a response message from the name server, wherein the response message contains the requested configuration information. 
         [0016]    In a variation on this embodiment, a name server receives a query message from a network node, wherein the query message contains a key that comprises an IP prefix and a string, wherein the IP prefix identifies a network node or a subnet, and the string specifies the type of configuration information. The name server then looks up the configuration information in a configuration database using the key. Finally, the name server sends a response message to the network node, wherein the response message contains the configuration information. 
         [0017]    In a variation on this embodiment, the IP prefix can include all of the bits of an IP address. 
         [0018]    In a variation on this embodiment, the key is created by first reversing the bytes of the IP prefix, and representing the reversed bytes of the IP prefix as a string. Next, a string that specifies the type of configuration information is prepended to the reversed-IP-prefix string. Finally, the string “.in-addr.arpa.” is appended to the resulting string to form the entire key. 
         [0019]    In a variation on this embodiment, the name server belongs to the Domain Name System (DNS). 
         [0020]    In a variation on this embodiment, the query message can be a DNS-query message. 
         [0021]    In a variation on this embodiment, the response message can be a DNS-response message. 
         [0022]    In a variation on this embodiment, the IP prefix can be an IP version 4 prefix or an IP version 6 prefix. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0023]      FIG. 1  illustrates a network that is connected to multiple network nodes, namely, a computer, an SMTP (Simple Mail Transfer Protocol) server, an NTP (Network Time Protocol) server, an NetBIOS (Network Basic Input Output System) server, a POP3 (Post Office Protocol 3) server, and a DNS (Domain Name System) name server containing configuration information in accordance with an embodiment of the present invention. 
           [0024]      FIG. 2  illustrates a DNS packet that contains multiple pieces of information that can be used by a network node, such as a computer, to exchange information with a DNS name server in accordance with an embodiment of the present invention. 
           [0025]      FIG. 3  illustrates the structure of a query that makes up the queries field in a DNS packet in accordance with an embodiment of the present invention. 
           [0026]      FIG. 4  illustrates the structure of a resource record that can be used by the DNS name server to provide information in response to a query in accordance with an embodiment of the present invention. 
           [0027]      FIG. 5  presents a flowchart illustrating a process that a network node, such as a computer, can use to lookup configuration information by querying a DNS name server containing configuration information in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
         [0029]    The data structures and code described in this detailed description are typically stored on a computer readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. This includes, but is not limited to, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (Compact Discs) and DVDs (Digital Versatile Discs or Digital Video Discs), and computer instruction signals embodied in a transmission medium (with or without a carrier wave upon which the signals are modulated). For example, the transmission medium may include a communications network, such as the Internet. 
       Network 
       [0030]      FIG. 1  illustrates a network  104  that is connected to multiple network nodes, namely, a computer  102 , an SMTP (Simple Mail Transfer Protocol) server  118 , an NTP (Network Time Protocol) server  120 , an NetBIOS (Network Basic Input Output System) server  122 , a POP3 (Post Office Protocol 3) server  124 , and a DNS (Domain Name System) name server containing configuration information  116  in accordance with an embodiment of the present invention. 
         [0031]    Network  104  can generally include any type of wire or wireless communication channel capable of coupling together network nodes. This includes, but is not limited to, a local area network, a wide area network, or a combination of networks. In one embodiment of the present invention, network  104  includes the Internet. 
         [0032]    A network node, such as a computer  102 , can generally include any type of communication device capable of communicating with other network nodes via a network. This includes, but is not limited to, a computer system based on a microprocessor, a mainframe computer, a server, a printer, a video camera, an external disk drive, a router, a switch, a personal organizer, and a mobile phone. 
         [0033]    Network  104  allows a source network-node, such as a computer  102 , to communicate with a target network-node, such as an SMTP server  118 . 
         [0034]    But, before the communication can take place, the source network-node, computer  102 , needs to know the name or the IP address of the target network-node, SMTP server  118 . Typically, such configuration information can be obtained by computer  102  using DHCP during system boot and can be stored for later use. 
       Configuration Information 
       [0035]      FIG. 1  illustrates a collection of configuration information  106  that can be stored on a computer  102  in accordance with an embodiment of the present invention. This collection of configuration information  106  includes one or more pieces of configuration information, such as, an SMTP server name  108 , an NTP server name  110 , a POP3 server name  112 , and a NetBIOS server name  114 . Among other uses, collection of configuration information  106  allows computer  102  to provide various services to its users. For example, computer  102  can use the SMTP server name  108 , which is part of collection of configuration information  106 , to communicate with the SMTP server  118 , thereby providing e-mail services to its end users. 
       Structure of a DNS Packet 
       [0036]      FIG. 2  illustrates a DNS packet  200  that contains multiple pieces of information that can be used by a network node, such as a computer  102 , to exchange information with a DNS name server  116  in accordance with an embodiment of the present invention. 
         [0037]    DNS-query packets and DNS-response packets both use the same DNS packet format. Specifically, a DNS packet  200  contains an identification field  202 , which allows a network node, such as a computer  102 , to match queries to the corresponding responses. DNS packet  200  also contains a flags field  204 , which among other things, indicates whether the DNS packet  200  is a query or a response. 
         [0038]    Furthermore, DNS packet  200  contains four variable-length fields, namely, queries  214 , response resource-records  216 , authority response-records  218 , and additional information response-records  220 . These variable-length fields are used for exchanging information between a network node, computer  102 , and a DNS name server  116 . 
         [0039]    Additionally, DNS packet  200  contains four other fields, namely, a number of queries field  206 , a number of response resource-records field  208 , a number of authority resource-records field  210 , and a number of additional information resource-records field  212 , which specify the number of entries in the four variable-length fields. 
       Structure of a Query 
       [0040]      FIG. 3  illustrates the structure of a query  300  that makes up the queries field  214  in accordance with an embodiment of the present invention. Query  300  contains a domain name field  302 , which specifies the domain name that is being queried. Furthermore, query  300  includes a query type field  304 , and a query class field  306 , which specifies the type and the class of the query  300 , respectively. 
       Structure of a Resource Record 
       [0041]      FIG. 4  illustrates the structure of a resource record  400  that can be used by a DNS name server  116  to provide information in response to a query in accordance with an embodiment of the present invention. 
         [0042]    Specifically, resource record  400  contains a domain name field  402 , which specifies the domain name under consideration. Resource record  400  also contains a resource-record type field  404  and a resource-record class field  406 , which specifies the type and class of the resource record, respectively. Additionally, resource record  400  includes a time to live field  408 , which specifies the amount of time (in seconds) that the resource record can be cached by a network node, such as a computer  102 . Furthermore, resource record  400  contains a resource data field  412 , which is a variable-length field that can be used by DNS name server  116  to provide information to the network node, computer  102 , in response to a query. Resource record  400  also contains a resource data length field  410 , which specifies the amount of data in the variable-length resource data field  412 . 
       Process of Looking up Configuration Information 
       [0043]      FIG. 5  presents a flowchart illustrating the process that a network node, such as a computer  102 , can use to lookup configuration information by querying a DNS name server containing configuration information  116  in accordance with an embodiment of the present invention. 
         [0044]    First, computer  102  creates a DNS-query packet  200 , which includes a query  300  containing a key (step  502 ). More specifically, the domain name  302  in the query  300  comprises the key, which is created by first reversing the bytes of the IP prefix and representing the reversed IP-prefix as a string. Next, a string that specifies the type of configuration information is prepended to the reversed-IP-prefix string. Finally, the string “.in-addr.arpa.” is appended to the resulting string form the entire key. Note that the string “.in-addr.arpa.” represents a special domain in DNS that is used for address-to-name mappings. 
         [0045]    For example, if the computer  102 , whose IP address is 17.255.12.34 with subnet mask 255.255.0.0, wants to lookup the NTP server name  110 , it would create a query  300  with domain name  302  that contains the key “4.dhcpopt.255.17.in-addr.arpa”, wherein “4.dhcpopt.” is a string that specifies the type of configuration information, “255.17” is a string representation of the reversed IP-prefix, and “.in-addr.arpa.” is the appended string. Note that, the string “4.dhcpopt.” refers to DHCP option 4, which corresponds to the NTP server name, as defined in IETF (Internet Engineering Task Force) RFC (Request for Comments) 2132. It will be readily apparent to one skilled in the art that every DHCP option defined in IETF RFC 2132 can be similarly converted into a string that specifies the type of configuration information. 
         [0046]    Next, the computer sends the DNS-query packet  200  (step  504 ) to a DNS name server containing configuration information  116 . The DNS name server containing configuration information  116  then receives the DNS-query packet  200  (step  506 ). Next, the DNS name server containing configuration information  116  looks up the configuration information in its database using the key in the query (step  508 ), which is contained in the DNS-query packet  200 . The DNS name server containing configuration information  116  then sends a response message containing the configuration information (step  510 ). Finally, computer  102  receives the response message (step  512 ) containing the configuration information, thereby allowing computer  102  to use the configuration information to perform its task. 
         [0047]    Furthermore, a network node, such as a computer  102 , can send multiple queries to the DNS name server containing configuration information  116  to lookup configuration information at different levels of granularity. For example, the network node can send a query containing the key “4.dhcpopt.34.12.255.17.in-addr.arpa” to find host-specific configuration that applies to that host alone. On the other hand, the network node can send a query containing the key “4.dhcpopt.255.17.in-addr.arpa” to find subnet-specific configuration information that applies to all network nodes on that subnet. Moreover, the network node can send a query containing the key “4.dhcpopt.17.in-addr.arpa” to find company-wide configuration information that applies uniformly to all the network nodes in a company. 
         [0048]    Note that DNS was designed so that network nodes could query it during normal system operation. Hence, by using DNS instead of DHCP to store configuration information, the present invention overcomes one of the limitations of DHCP, in which the network node was restricted to lookup configuration information during system boot only. Furthermore, a network node can keep its configuration information up to date by periodically querying a DNS name server containing configuration information. Moreover, in the present invention, the type of configuration information is specified by an arbitrary string, such as “4.dhcpopt.”. Hence, the present invention can potentially support infinite types of configuration information, whereas DHCP can support only up to 255 types of configuration information. 
         [0049]    The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.