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Date: Wed, 14 Feb 2024 15:28:28 -0800
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Subject: Win 11 Cygwin dns-utils "dig" and "host": Option -6 causes command to
 timeout
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From: Jim Garrison via Cygwin <cygwin@cygwin.com>
Reply-To: jhg@acm.org
Cc: Jim Garrison <jhg@jhmg.net>
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Win 11 Cygwin "dig" and "host": Option -6 causes command to hang

TL;DR
-----

It appears "dig" and "host" both depend on the existence of 
/etc/resolv.conf, but only when the -6 option (send queries over IPv6) 
is specified.

/etc/resolv.conf does not exist on either my old Win 10 or relatively 
new Win 11 systems.

I have a vague recollection that at some point, maybe Windows 7 or even 
XP, there was a Cygwin /etc/resolv.conf that was a link to 
C:\windows\system32\drivers\etc\resolv.conf, but I don't think this has 
been true for quite a while if it ever was.  Also resolv.conf does not 
exist in the windows location either.

Details
-------

Sample:

     # Default query over IPv4
     $ host google.com
     google.com has address 74.125.197.102
     google.com has address 74.125.197.100
     google.com has address 74.125.197.138
     google.com has address 74.125.197.101
     google.com has address 74.125.197.139
     google.com has address 74.125.197.113
     google.com has IPv6 address 2607:f8b0:400e:c03::64
     google.com has IPv6 address 2607:f8b0:400e:c03::71
     google.com has IPv6 address 2607:f8b0:400e:c03::65
     google.com has IPv6 address 2607:f8b0:400e:c03::66
     google.com mail is handled by 10 smtp.google.com.


     # Query over IPv6
     $ host -6 google.com
     ;; connection timed out; no servers could be reached

     # Query over IPv6 with explicit DNS server
     $ host -6 google.com 2601:xxx:xxx:xxx:201:2eff:fe70:3bfe
     Using domain server:
     Name: 2601:xxx:xxx:xxx:201:2eff:fe70:3bfe
     Address: 2601:xxx:xxx:xxx:201:2eff:fe70:3bfe#53
     Aliases:

     google.com has address 74.125.197.139
     google.com has address 74.125.197.113
     google.com has address 74.125.197.102
     google.com has address 74.125.197.100
     google.com has address 74.125.197.138
     google.com has address 74.125.197.101
     google.com has IPv6 address 2607:f8b0:400e:c03::71
     google.com has IPv6 address 2607:f8b0:400e:c03::65
     google.com has IPv6 address 2607:f8b0:400e:c03::66
     google.com has IPv6 address 2607:f8b0:400e:c03::64
     google.com mail is handled by 10 smtp.google.com.

I ran the failing command above in strace and saw that it's trying to 
open /etc/resolv.conf

     [...]
       206  515079 [main] host 2426 open: open(/etc/resolv.conf, 0x0)
        58  515137 [main] host 2426 normalize_posix_path: src 
/etc/resolv.conf
        59  515196 [main] host 2426 normalize_posix_path: 
/etc/resolv.conf = normalize_posix_path (/etc/resolv.conf)
        63  515259 [main] host 2426 mount_info::conv_to_win32_path: 
conv_to_win32_path (/etc/resolv.conf)
        68  515327 [main] host 2426 mount_info::cygdrive_win32_path: src 
'/etc/resolv.conf', dst ''
        61  515388 [main] host 2426 mount_info::conv_to_win32_path: 
src_path /etc/resolv.conf, dst C:\cygwin64\etc\resolv.conf, flags 
0x30008, rc 0
        81  515469 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtCreateFile (\??\C:\cygwin64\etc\resolv.conf)
        82  515551 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf)
        90  515641 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtCreateFile (\??\C:\cygwin64\etc\resolv.conf.exe)
        81  515722 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf.exe)
        90  515812 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtCreateFile (\??\C:\cygwin64\etc\resolv.conf.lnk)
        81  515893 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf.lnk)
        88  515981 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtCreateFile (\??\C:\cygwin64\etc\resolv.conf.exe.lnk)
        82  516063 [main] host 2426 symlink_info::check: 0xC0000034 = 
NtQueryInformationFile (\??\C:\cygwin64\etc\resolv.conf.exe.lnk)
        81  516144 [main] host 2426 symlink_info::check: 0 = 
symlink.check(C:\cygwin64\etc\resolv.conf, 0x7FFFFB4B0) (mount_flags 
0x30008, path_flags 0x0)
        64  516208 [main] host 2426 mount_info::conv_to_win32_path: 
conv_to_win32_path (/etc)
        59  516267 [main] host 2426 mount_info::cygdrive_win32_path: src 
'/etc', dst ''
        60  516327 [main] host 2426 mount_info::conv_to_win32_path: 
src_path /etc, dst C:\cygwin64\etc, flags 0x30008, rc 0
        69  516396 [main] host 2426 symlink_info::check: 0x0 = 
NtCreateFile (\??\C:\cygwin64\etc)
       233  516629 [main] host 2426 symlink_info::check: not a symlink
        65  516694 [main] host 2426 symlink_info::check: 0 = 
symlink.check(C:\cygwin64\etc, 0x7FFFFB4B0) (mount_flags 0x30008, 
path_flags 0x0)
        62  516756 [main] host 2426 path_conv::check: 
this->path(C:\cygwin64\etc\resolv.conf), has_acls(1)
        61  516817 [main] host 2426 build_fh_pc: fh 0x80000BE18, dev 
000000C3
        60  516877 [main] host 2426 fhandler_base::open: 
(\??\C:\cygwin64\etc\resolv.conf, 0x0)
        89  516966 [main] host 2426 seterrno_from_nt_status: 
/cygdrive/d/a/scallywag/cygwin/cygwin-3.5.0-1.x86_64/src/newlib-cygwin/winsup/cygwin/fhandler/base.cc:717 
status 0xC0000034 -> windows error 2
        75  517041 [main] host 2426 geterrno_from_win_error: windows 
error 2 == errno 2
        59  517100 [main] host 2426 fhandler_base::open: 0xC0000034 = 
NtCreateFile (0x7FF84CA3A060, 0x80100000, 
\??\C:\cygwin64\etc\resolv.conf, io, NULL, 0x0, 0x7, 0x1, 0x4020, NULL, 0)
        85  517185 [main] host 2426 fhandler_base::open: 0 = 
fhandler_base::open(\??\C:\cygwin64\etc\resolv.conf, 0x0)
        90  517275 [main] host 2426 fhandler_base::open_fs: 0 = 
fhandler_disk_file::open(\??\C:\cygwin64\etc\resolv.conf, 0x0)
        90  517365 [main] host 2426 open: -1 = open(/etc/resolv.conf, 
0x0), errno 2
     [...]

I confirmed this was the problem by creating /etc/resolv.conf (within 
the Cygwin root, not a symlink) and included the search domain and IPv4 
and IPv6 dns servers, after which the -6 option no longer timed out.

-- 
Jim Garrison
jhg@acm.org

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