Electrical computers and digital processing systems: multicomput – Computer network managing – Network resource allocating
Reexamination Certificate
1998-12-08
2002-07-30
Winder, Patrice (Department: 2155)
Electrical computers and digital processing systems: multicomput
Computer network managing
Network resource allocating
C709S228000
Reexamination Certificate
active
06427170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to management of data communications networks. More particularly, the present invention relates to an IP (Internet Protocol) address management system and method for managing IP addresses on a data communications network utilizing dynamic IP address assignment.
2. The Background
Data communications networks are widespread and there are many different types of networks, including LANs (Local Area Networks), MANs (Metropolitan Area Networks), and WANs (Wide Area Networks). They are used for providing numerous services, both for companies and for individuals. They provide a powerful communication mechanism and allow access to various kinds of remote information. Two or more networks connected together form an internetwork (or internet). The “Internet” is a worldwide internet widely used to connect universities, government offices, companies, and private individuals. Every host (or end-user's machine running user applications) and router interface on the Internet has an IP address, which encodes its network number and host number. The combination is unique and no two machines have the same IP address. IP addresses are typically 32 bits long and are used in the source address and destination address fields of IP packets. The Source Address is the ultimate source of the IP packet; the Destination Address is the ultimate destination of the IP packet.
FIG. 1
illustrates IP address formats well known to those of ordinary skill in the art. The IP address formats are divided into five classes. The class A format, which begins with a “0” bit for indicating the class and has a 7-bit network address field and a 24-bit host address field, allows up to 126 networks with 16 million hosts each. The class B format beginning with the bit pattern “10” allows 16382 networks with up to 64K hosts each. The class C format beginning with the bit pattern “110” allows 2 million networks (e.g., LANS) with up to 254 hosts each. The class D format beginning with “1110” is for multicast in which a packet is directed to multiple hosts. Finally, the Class E format beginning with the bit pattern “11110” is reserved for future use. Network numbers are assigned by the InterNIC (Internet Network Information Center) or another administrative body in order to avoid conflicts.
These binary IP addresses are, however, rarely used by computer programs and humans to refer to hosts, mailboxes (for email), and other resources. Instead of binary numbers, ASCII strings, such as “company.com” are used. In order to avoid host name conflicts, these names are managed by the Domain Name System (DNS) (central to a domain), the Internet's official naming system. The DNS provides a hierarchical, domain-based naming scheme and a distributed database system for implementing this naming scheme. That is, conceptually, the Internet is divided into several hundred top-level domains, where each domain covers many hosts. Each domain is partitioned into subdomains, which are further partitioned, and so on.
In the hierarchical scheme, each domain controls how it allocates its subdomains (i.e., the domains under it). To create a new domain, permission is required of the domain in which it will be included. Once a new domain has been created and registered, it can create subdomains without permission from any higher domain, and keep track of all of its own subdomains. The DNS is primarily used for mapping host names to IP addresses, but it can be used for other purposes.
Every domain, whether it represents a single host or is a top-level domain, can have a set of resource records associated with it. A resource record is, for example, a five-tuple including the fields of Domain_name, Time_to_live, Class, Type, and Value. The Domain_name field tells the domain to which the record applied, and thus the primary search key used to satisfy queries. When a query is made about a domain, all the matching records of the class requested are returned by the DNS. The Time_to_live field gives an indication of how stable the record is. Information that is highly stable is assigned a large value, such as 86400 (the number of seconds in one day). Information that is highly volatile is assigned a small value, such as 60 (one minute). For Internet information, the Class field is always “IN”. The Type field tells what kind of record this is. The important types are, for example, SOA (Start of Authority), A (Address), MX (Mail exchange), NS (Name Server), PTR (Pointer), HINFO (Host information), TXT (Text), and the like. Finally, the Value field provides an actual value for the record. For example, an SOA record provides the name of the primary source of information about the name server's zone (described below), and its value is parameters of this zone. The most important record type is the A (Address) record. It holds a 32-bit IP address for a certain host. Every Internet host must have at least one IP address, so that other machines can communicate with it. Some hosts have two or more network connections (through different interfaces), in which case they will have one type A resource record (e.g., IP address) per network connection.
The naming scheme of the DNS is implemented as a corresponding hierarchical database system. The DNS name space is divided up into non-overlapping zones. Each zone contains name servers holding the authoritative information about the zone. Normally, a zone has one primary name server and one or more secondary name servers. The primary server gets its information from a file on its disk, and secondary servers get their information from the primary name server.
To obtain resource records for a domain name, for example, to get the IP address for a host name, an application program calls a library procedure called the resolver, passing it the domain name as a parameter. The resolver sends a UDP (User Datagram Protocol) packet to one of the local name servers. For example, to map a host name onto an IP address, a resolver can send a query about the host name to a local name server. If the local name server has resource records for the domain (that is, the local name server has jurisdiction over the host name being sought), it returns the authoritative resource records. The “authoritative” record is one that comes from the authority that manages the record and thus is always correct.
If, however, the domain is remote and no information about the requested domain is available locally, the name server sends a query message to the top-level name server for the domain requested. For example, when a user (DNS client) in San Francisco (SF) makes a query about John.rd.company.com for a local name server in SF, which does not have records for the host, the SF name server sends a UDP packet to the server for corn given in its database, com-server.net. It is unlikely that the com-server.net knows John.rd.company.com or rd.company.com, but it definitely knows company.com that is one of its own subdomains. Thus, com-server.net forwards the inquiry to company.com. In turn, company.com forwards the request to rd.company.com, which must have the authoritative resource records. The resource records requested are sent backward from rd.company.com to the SF name server.
Once these records get back to the SF name server, they will be entered into a cache there (local cache), in case they are needed later. However, this information is not authoritative, since changes made at rd.company.com will not be propagated to all the caches of local name servers that may know about it. For this reason, entries in a local cache should not live too long (i.e., the Time_to_live field is set to a small value).
The above query method is recursive, since each server that does not have the requested information goes and finds it somewhere, then reports back. Alternatively, when one local name server fails to find the desired records, it may return the name of the next local name server along the line to try. For example, SF name server may give the name of the San Jose name ser
Bhasham Sampath Kumar Sthothra
Dos Santos Maria Alice
Lou Shuxian
Sitaraman Aravind
Zhang Shujin
Cisco Technology Inc.
Ritchie David B.
Winder Patrice
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