Re: multihomed connections
Date: Tue, 8 Jun 2004 11:38:05 -0700
On Tue, Jun 08, 2004 at 08:18:40PM +0200, Gisle Vanem wrote:
> The other "bug" in libcurl is not a bug at all, but rather inconsitent
> behaviour depending on which resolver is used.
> Without C-ares (i.e. USE_THREADING_GETADDRINFO):
> >set CURL_TRACE=1
> >curl -v4 http://ubr4-ca5-0-sec.landg1.lb.home.nl
> * Couldn't find host ubr4-ca5-0-sec.landg1.lb.home.nl in the .netrc file, using defaults
> 416: not yet
> 139: dump_addrinfo:
> fam 2, CNAME <none>, 10.221.110.1
> fam 2, CNAME <none>, 126.96.36.199
> fam 2, CNAME <none>, 10.243.112.1
> fam 2, CNAME <none>, 188.8.131.52
> fam 2, CNAME <none>, 184.108.40.206
> fam 2, CNAME <none>, 220.127.116.11
> fam 2, CNAME <none>, 18.104.22.168
> 353: getaddrinfo_thread() status 0, thread retval 0, 361: elapsed 15 ms
> * About to connect() to ubr4-ca5-0-sec.landg1.lb.home.nl port 80
> * Connect failed; Connection refused
> * Closing connection #0
> curl: (7) Connect failed; Connection refused
> Okay, the "refused" came from the last IP. Using tcpdump, I see curl
> tries the addresses in the above order. But with a C-ares version, the
> result is "timed out". Since the last IP it tried was 10.221.110.1.
> It would be nice if libcurl could tell us all the IP it tried and the result of
> each failed attempt.
> I.e. C-ares returns a completely different IP-order compared to what getaddrinfo()
> says. It looks like the DNS for this host is misconfigured too. Isn't addresses
> supposed to be listed in *prefered* order?
If the DNS server is configured for round-robin, then the "preferred"
order is to balance requests evenly over the various addresses. The
preferred address could be different each time.
> BTW. try "adig www.cnn.com" and watch the IP-order changes constantly.
> Whereas the dig or host programs gives a more stable list of IPs.
I'll bet adig does a new DNS request each time, whereas dig and host return
a cached result.
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