They are mathematically produced and allocated by the Internet Assigned Numbers Authority (IANA), a division of the Internet Corporation for Assigned Names and Numbers (ICANN). Each number in the set can range from 0 to 255. IP addresses are expressed as a set of four numbers - an example address might be 192.158.1.38. IP addresses provide a way of doing so and form an essential part of how the internet works.Īn IP address is a string of numbers separated by periods. The internet needs a way to differentiate between different computers, routers, and websites. In essence, IP addresses are the identifier that allows information to be sent between devices on a network: they contain location information and make devices accessible for communication. IP stands for "Internet Protocol," which is the set of rules governing the format of data sent via the internet or local network. Not just pull the first IP address off the list.Īdvanced DNS Round Robin and Destination IP address selection on Windows Clients.An IP address is a unique address that identifies a device on the internet or a local network. There is a change in behavior when IPv6 is installed, so the OS does The longest match is used, not just the first IP address off the list. Similarly, ifĬommonPrefixLen(DA, Source(DA)) < CommonPrefixLen(DB, Source(DB)), When DA and DB belong to the same address family (both are IPv6 orīoth are IPv4): If CommonPrefixLen(DA, Source(DA)) >ĬommonPrefixLen(DB, Source(DB)), then prefer DA. There are 10 rules, but rule 9 should be considered : Rule 9: Use longest matching prefix. Only act as tie-breakers for earlier rules. Result then the remaining rules are ignored, as subsequent rules The pair-wise comparison of destination addresses consists of ten TheĪlgorithm sorts together both IPv6 and IPv4 addresses. It is specified here in terms of the pair-wise comparison of addressesĭA and DB, where DA appears before DB in the original list. The destination address selection algorithm takes a list ofĭestination addresses and sorts the addresses to produce a new list. IPv6 introduces a change in this behavior per What address the client will use by putting it at the top of the list. This works well with DNS Round Robin as it lets the Server decide RFC 1794 - DNS Support for Load Balancing.įor IPv4, destination address selection is fairly simple and usuallyĭone by selecting the first IP address returned by the DNS server. Only moving to the next if the previous one failed. When receiving a list of IPs, will just pick up the first one, This is based on the fact the most applications, It will attempt a round-robin method for reordering the list on each When a DNS server returns a a list of IP addresses for a DNS query, IP address is for determining the closest result. Netmask ordering is another mechanism for further optimizing which.IP address from the list returned by a DNS server, so that not allĬlients get the same IP address every time. DNS Round Robin is the main mechanism for choosing an.In a nutshell there are two main mechanisms : Such programs generally do not support anything but IPv4. Very old programs might only attempt the "first" IPv4 address (which address is "first" is unpredictable), as the older OS-provided "hostname lookup" functions couldn't return more than one. Some programs (mainly web browsers) try both types in parallel, while others merge both into a single list which is sorted into broad categories (native global IPv6 addresses, then native IPv4, then private IPv6, etc). There are really two lists at DNS level – one for IPv4 addresses (A records) and another for IPv6 (AAAA). The program will usually use whatever order it gets from the OS, but the OS might shuffle the list again before returning it (just in case the DNS server did not). ¹ (There are a few reasons why even a single server having multiple addresses may perform better than the exact same setup with just one address.) This might be done both by the authoritative server and/or by your local resolver. Often the answer is deliberately shuffled to provide some basic load-balancing¹. Values in DNS do not have an inherent order (and the A record itself has no priority field), so the DNS server might return the A records in any order the expectation is that all addresses listed for a given name will be providing identical service. Usually programs try all addresses in the list until one responds. There is no strict rule, as all addresses are equivalent and the program can use them in any order.
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