Re: nscd and DNS cache
On 05/16/2012 10:39 AM, Ed Greshko wrote:
On 05/17/2012 12:28 AM, Greg Woods wrote:On Thu, 2012-05-17 at 00:13 +0800, Ed Greshko wrote:when you do a look up on www.cnn.com it will return 4 IP addresses. Now, since bind would have that in its cache it wouldn't have to send out a query. What I don't know is if an application would make a request would the list be returned in the same order every time to the requesting application? In other words, if the TTL is not set low, would that defeat the round robin technique.Unfortunately, there is no guarantee that a client resolver will actually use the IP addresses in the order they are presented by the DNS server. Nothing in the DNS spec requires them to do so.Yeah.... I know there is no spec... I'm just expecting the clients to be "dumb" and take the first one in the stack. :-) :-)Interesting things to investigate.....if I really had the time.My experience says that DNS round robining is actually a poor method of load balancing. I'm surprised to see a large site like CNN resorting to this (if that's really what they are doing this for). Perhaps in combination with a low TTL and a modified DNS server, they can send out a completely different set of IPs every few minutes, and achieve a sort of crude load balancing that way, but I think load balancing works better if you just send out a single IP and use a load balancer that you can control, such as LVS (Linux Virtual Server) that can farm out incoming connections to a single virtual address out to multiple real addresses.Yes... I suppose one also has to ask if the load balancing is meant to be server or network balancing.
Well, after running dnsmasq with the configuration I just emailed,I see the following behavior of firefox vs. running nslookup on command line.
FF, even after resolving google.com only a minute ago, is still spinning saying:
lookup up www.google.com whereas , on the command line, I run nslookup www.google.com and almost instantly, I get Server: 127.0.0.1 Address: 127.0.0.1#53 Non-authoritative answer: Name: google.com Address: 184.108.40.206 Name: google.com Address: 220.127.116.11 Name: google.com Address: 18.104.22.168 Name: google.com Address: 22.214.171.124 Name: google.com Address: 126.96.36.199 Name: google.com Address: 188.8.131.52 Name: google.com Address: 184.108.40.206 Name: google.com Address: 220.127.116.11 Name: google.com Address: 18.104.22.168 Name: google.com Address: 22.214.171.124 Name: google.com Address: 126.96.36.199 and FF is still spinning waiting for the resolution. Does anyone see this discrepancy? -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
[Older Fedora Users] [Fedora Announce] [Fedora Package Announce] [EPEL Announce] [Fedora News] [Fedora Cloud] [Fedora Advisory Board] [Fedora Education] [Fedora Security] [Fedora Scitech] [Fedora Robotics] [Fedora Maintainers] [Fedora Infrastructure] [Fedora Websites] [Anaconda Devel] [Fedora Devel Java] [Fedora Legacy] [Fedora Desktop] [Fedora Fonts] [ATA RAID] [Fedora Marketing] [Fedora Management Tools] [Fedora Mentors] [SSH] [Find Someone Special] [Fedora Package Review] [Fedora R Devel] [Fedora PHP Devel] [Kickstart] [Fedora Music] [Fedora Packaging] [Centos] [Fedora SELinux] [Fedora Legal] [Fedora Kernel] [Fedora QA] [Fedora Triage] [Fedora OCaml] [Coolkey] [Virtualization Tools] [ET Management Tools] [Yum Users] [Tux] [Yosemite News] [Yosemite Photos] [Linux Apps] [Maemo Users] [Gnome Users] [KDE Users] [Fedora Tools] [Fedora Art] [Fedora Docs] [Maemo Users] [Asterisk PBX] [Fedora Sparc] [Fedora Universal Network Connector] [Libvirt Users] [Fedora ARM]