Date: Thu, 27 Feb 2020 22:45:30 -0800 From: Doug Hardie <bc979@lafn.org> To: Dewayne Geraghty <dewayne@heuristicsystems.com.au> Cc: freebsd-questions@freebsd.org Subject: Re: DNS resolution Message-ID: <16E91023-D8C4-4A40-9EBA-183443D610B2@mail.sermon-archive.info> In-Reply-To: <028a9ca5-b935-3de1-5edd-adb959c1116a@heuristicsystems.com.au> References: <93893C00-93BD-4C71-943E-8751DF2854FE@mail.sermon-archive.info> <028a9ca5-b935-3de1-5edd-adb959c1116a@heuristicsystems.com.au>
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> On 27 February 2020, at 22:22, Dewayne Geraghty = <dewayne@heuristicsystems.com.au> wrote: >=20 > On 28/02/2020 11:34 am, Doug Hardie wrote: >> I have encountered an inconsistent result in DNS resolution that I am = unable to explain. The situation is three servers with completely = different IP addresses on three different internet connections. All = three are via different companies. In the DNS records for the domain I = have an A record for each server with the name A.domain, B.domain, and = C.domain. Each points to the appropriate IP address. The name = www.domain (and also just domain) have 3 A records: one for each of the = 3 servers. The goal is to have a fail over such that A is the primary = server, and if it fails, then try B, and finally C. Load balancing is = not desirable because the web transactions require numerous exchanges = and need to all use the same server. >>=20 >> On Frontier, Spectrum, and Charter connections, host www.domain lists = the 3 servers in the order they are defined in the DNS records. Every = time I run host I get the same result. However, there is one PC running = windows 10 that connects via the charter supplied modem and is = configured for DNS at the modem address that gets the addresses in = random order. It appears to be trying to do load balancing. When I use = Charter's official DNS servers, I don't see that. But if I use the = modem then even FreeBSD 11.1 gets the random results. >>=20 >> The spectrum interface has the same issue. The official DNS servers = are consistent, the modem as a DNS server is random. I thought the TTL = for the domain would be honored by the DNS servers. That doesn't always = appear to be the case, or the modem DNS servers are rotating their = responses from their cache. However, shouldn't the client computers = cache the DNS response? Windows does not appear to be doing that. >>=20 >>=20 > Yes, Windows boxes cache the results, to check, open cmd prompt > ipconfig /displaydns >=20 > I'd suggest that the modem isn't caching and rotating dns responses as > expected. I can't see what DNS servers the modem is using, but I suspect they are = the "official" ones per the ISP. When I use those directly, there is no = rotating. When I go to the modem with either windows or FreeBSD then I = get rotation. I don't see where else the rotation could be occurring. =20= -- Doug
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