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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: .ORG problems this evening
On Thu, 18 Sep 2003, just me wrote: : If you're still confused, have a read here: : : http://www.ultradns.com/support/managed_dns_faq.cfm : : "Q. I read that your service is supposed to make use of several : servers all over the world, but you only give users two server : addresses to provide to their registrar. How do I make use of all the : other servers?" "I know what anycast does." See the other sister thread. The problem is that their answer is frankly *wrong*: A. The two server addresses you supply your registrar when you set up a domain on the UltraDNS system are actually 'virtual' addresses that will route to the best possible server on our network, based on a number of factors. This highly intelligent mechanism allows you to achieve full redundancy and reliability with only two name server addresses actually listed. In fact, if the registrar would allow you to do so, you could achieve the same level of reliability with only one name server address. Anycast is *NOT* a "redundancy and reliability" system when dealing with application-based services like DNS. Rather, anycast is a geographically biased traffic distribution system. There is a subtle but important difference here: DNS site A advertises anycast networks 1.2.3.0/24 and 1.2.4.0/24. DNS site B advertises anycast networks 1.2.3.0/24 and 1.2.4.0/24. Host site C attempts to use DNS servers from DNS sites A or B based on best anycast route selection. Host site C's router happens to pick DNS site A as best route for both 1.2.3.0/24 and 1.2.4.0/24. DNS site A goes down, but its BGP advertisements are still in effect. (Their firewall still appears to be up, but DNS requests fail.) Host site C cannot resolve ANYTHING from DNS site A, even though DNS site B is still up and running. But host site C cannot see DNS site B! Get the picture yet? -- -- Todd Vierling <[email protected]> <[email protected]>
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