Win 11 Cygwin dns-utils "dig" and "host": Option -6 causes command to timeout
Brian Inglis
Brian.Inglis@SystematicSW.ab.ca
Fri Feb 16 15:34:51 GMT 2024
On 2024-02-15 10:56, Jim Garrison via Cygwin wrote:
> On 2/14/2024 17:08, Brian Inglis via Cygwin wrote:
>> On 2024-02-14 16:28, Jim Garrison via Cygwin wrote:
>>> Win 11 Cygwin "dig" and "host": Option -6 causes command to hang
>> Ditto!
>>
>> Without IPv6 nameservers in /etc/resolv.conf I get:
>>
>> $ host -6 google.com
>> ;; connection timed out; no servers could be reached
>> Failing assertion due to probable leaked memory in context 0xa00020be0 ("dig")
>> (stats[4].gets == 1).
>> mem.c:1121: INSIST(ctx->stats[i].gets == 0U) failed.
>>
>> but with IPv6 nameservers in /etc/resolv.conf I get:
>>
>> $ host -6 google.com
>> google.com has address 142.251.211.238
>> google.com has IPv6 address 2607:f8b0:400a:804::200e
>> google.com mail is handled by 10 smtp.google.com.
>> I added a Cygwin postinstall script:
>>
>> /etc/postinstall/0p_l_etc_resolv_conf.dash
>>
>> to create resolv.conf from `ipconfig /all` DNS servers, an internal list of
>> open public DNS servers, and search domains, update:
>>
>> /var/run/resolvconf/resolv.conf
>>
>> when changed, and `ln -frsvt /etc/`, also run from a Scheduled Task on System
>> Restart.
> Unfortunately, this is only a partial solution because your delegated prefix can
> change if your ISP changes it. The firewall knows how to track this, and will
> issue a new LAN IP address at the next lease expiration. But, the firewall is
> also providing name resolution, and after its LAN prefix changes (and the grace
> period expires) Cygwin's name resolultion would be left pointing to a
> non-existent address.
That is why I run the resolv.conf postinstall script to check and change
/etc/resolv.conf near the start of Cygwin Setup postinstall, and after Windows
restart.
You can set up the cron daemon or Scheduled Tasks to do this whenever you need,
or if you run a change detection script, it could do so: it only changes the
installed file if the generated file contents differ.
> Also, IPv4 resolution does not seem to depend on resolv.conf, and Windows
> clearly does not depend on resolv.conf for either IPv4 or IPv6. Maybe Cygwin
> should just ask Windows for the name servers?
That's what my resolv.conf setup script does with Windows `ipconfig /all` output.
> As a counterpoint I note that on dual stack Linux one DOES need an extra daemon
> (resolvconf or systemd-resolved) to manage merging of IPv4 and IPv6 DHCP
> configurations. Without one of those, the IPv6 client overwrites the
> resolv.conf created by the IPv4 client.
That's why I create /var/run/resolvconf/resolv.conf for compatibility then
symlink to /etc/resolv.conf (and my /var/run is a compatibility symlink to /run/).
> Maybe Cygwin needs the equivalent of resolvconf? I found references to a file
> called resolvconf in the sources/devel packages for unbound, but unbound itself
> doesn't seem to contain anything with that name. Also unbound seems to be
> currently unmaintained.
Windows does not discriminate between IP v4 and v6 DNS name servers, but
unfortunately Cygwin does not support a/hosts/v4/v6 enumeration.
Have a look at the attached scripts, try them out on your system, and adapt them
to do what you want with them: treat them as Public Domain; they have some
tweaks to support some open public DNS name servers as backups for my ISP's, and
tweaks for that ISP and my preferences, but unsure if "search" list suffixes
work or affect anything?
--
Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
La perfection est atteinte Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer but when there is no more to cut
-- Antoine de Saint-Exupéry
-------------- next part --------------
#!/usr/bin/awk -f
# cyg-resolv.awk - create Cygwin resolv.conf from Windows ipconfig /all output
BEGIN {
# ISP domains
isp_domains = "shaw[^.]*[.]|sjrb[.]"
isp = "shaw.ca."
# suffixes
SUF = "ca. uk. org. com. net. edu."
# public name servers Quad 9, Cloudflare, Open DNS, Google, Comodo
NS = "dns.quad9.net. one.one.one.one. " \
"resolver2.opendns.com. resolver1.opendns.com. " \
"google-public-dns-b.google.com. google-public-dns-a.google.com. " \
"ns2.recursive.dnsbycomodo.com. ns1.recursive.dnsbycomodo.com. " \
""
# CleanBrowsing
# "security-filter-dns.cleanbrowsing.org. " \
# "adult-filter-dns.cleanbrowsing.org. " \
# "family-filter-dns.cleanbrowsing.org. " \
# CIRA Canadian Shield Protected+malware+phishing
# "CAshieldProtected" \
# resolv.conf comments
CFHD = "# /etc/resolv.conf"
CFHD = CFHD " - Internet Domain Name System resolver configuration file"
CDS = "# domain suffix"
CSSL = "# suffix search list"
# hosts command
hosts = "/usr/bin/getent ahosts"
# IP v4
# digit patterns: [0-9], [1-9], [6-9], [0-4], [0-5], [0[0]]0-255, .[0[0]]0-255, .[0]16-31
z9 = "[0-9]"
o9 = "[1-9]"
s9 = "[6-9]"
z4 = "[0-4]"
z5 = "[0-5]"
p0_255 = "(0{0,2}" z9 "|0{0,1}" o9 z9 "|1" z9 z9 "|2(" z4 z9 "|5" z5 "))"
d0_255 = "(." p0_255 ")"
d16_31 = ".0?(1" s9 "|2" z9 "|3[01])"
ipv4 = "^" p0_255 d0_255 "{3}$"
# private subnets
# 10.0.0.0-.255.255.255
p10 = "^10" d0_255 "{3}$"
# 169.254.0.0-.255.255 Zeroconf Link-Local (IPv4LL) Automatic Private IP Addressing (APIPA)
p169 = "^169.254" d0_255 "{2}$"
# 172.16.0.0-.31.255.255
p172 = "^172" d16_31 d0_255 "{2}$"
# 192.168.0.0-.255.255
p192 = "^192.168" d0_255 "{2}$"
# IP v6
# hex, id
px = "[0-9A-Fa-f]"
gx = px "{0,4}"
cx = ":" gx
id = "[0-9A-Za-z]"
ipv6 = "^" gx "(" cx "){1,7}" "(%" id "+)?$"
# private subnets
# fc00::/7 fc-fe + ff bit 7 local
pfc00 = "^[Ff][C-Fc-f]" px "{2}:"
# seen to avoid duplication
used["127.0.0.1"] = "127.0.0.1"
}
function nextaddr( addr, name, ns, nameserveraddr, nameserverhostname ,private,n) {
if (DEBUG) print addr, name, ns > DEBUG
# private subnets
if (!(addr in used || addr ~ p10 || addr ~ p169 || addr ~ p172 || addr ~ p192 || addr ~ pfc00)) {
n = ++ns
if (addr) { nameserveraddr[n] = addr }
if (name) { nameserverhostname[n] = name }
if (DEBUG) print addr, name, ns > DEBUG
used[addr] = addr
}
return ns
}
function addrs( NS, nameserveraddr, ns ,c) {
# $ getent ahosts $NS
# 1.0.0.1 STREAM one.one.one.one
# 1.0.0.1 DGRAM one.one.one.one
# 1.1.1.1 STREAM
# 1.1.1.1 DGRAM
# 149.112.112.112 0 dns.quad9.net
# 9.9.9.9 0
# 208.67.220.220 0 resolver2.opendns.com
# 208.67.222.222 0 resolver1.opendns.com
# 8.8.4.4 0 google-public-dns-b.google.com
# 8.8.8.8 0 google-public-dns-a.google.com
# 149.112.122.20 0 CAshieldProtected
# 149.112.121.20 0
c = hosts " " NS
while ((c | getline) > 0) {
ns = nextaddr( $1, $3, ns, nameserveraddr, nameserverhostname)
}
close( c )
return ns
}
/\r/ { sub( /\r/, "", $NF) } # trim \r
# collect DNS domain suffixes
/D[Nn][Ss]\sSuffix[^:]*:\s\S/ {
last = $NF
if (last ~ /\./ && last !~ /\.$/) last = last "."; # add root dot
if (!(last in domain)) {
domain[last] = last
domains = domains " " last
}
while (last ~ /\..+\..+/) { # strip labels if more than two for domain
sub(/^[^.]+./, "", last)
if (last ~ /\./ && last !~ /\.$/) last = last "."; # add root dot
if (!(last in domain)) {
domain[last] = last
domains = domains " " last
}
}
}
# collect DNS search suffixes
/Search\sList[^:]*:\s\S/ {
for (d in domain) {
if (!(d in search)) search[d] = d
if (d ~ isp_domains) {
last = isp
if (!(last in search)) {
search[last] = last
domains = domains " " last
}
}
}
last = $NF
if (last ~ /\./ && last !~ /\.$/) last = last "."; # add root dot
if (!(last in search)) {
search[last] = last
domains = domains " " last
}
while (last ~ /\..+\..+/) { # strip labels if more than two for domain
sub(/^[^.]+./, "", last)
if (last ~ /\./ && last !~ /\.$/) last = last "."; # add root dot
if (!(last in search)) {
search[last] = last
domains = domains " " last
}
}
ns = split( SUF, sa)
for (s = 1; s <= ns; ++s) {
last = sa[s]
if (last ~ /\./ && last !~ /\.$/) last = last "."; # add root dot
if (!(last in search)) {
search[last] = last
domains = domains " " last
}
}
}
# collect DNS server IP addresses
/DNS\sServers[^:]*:\s\S/ { dns = 1 } # start - enable
dns && ($NF ~ ipv4 || $NF ~ ipv6) { # collect IP addrs
ns = nextaddr( $NF, last, ns, nameserveraddr, nameserverhostname)
last = ""
}
dns && $NF !~ ipv6 && $NF !~ ipv4 { dns = 0 } # non-IP disable
# output unique resolv.conf entries
END {
print CFHD
ns = addrs( NS, nameserveraddr, ns)
for (n = 0; n <= ns; ++n) {
if (n in nameserverhostname && nameserverhostname[n]) {
print "#", nameserverhostname[n]
}
if (n in nameserveraddr && nameserveraddr[n]) {
print "nameserver", nameserveraddr[n]
}
}
print CDS
for (d in domain) { print "domain " d }
print CSSL
if (domains) print "search" domains
}
-------------- next part --------------
#!/bin/dash
# 0p_l_etc_resolv_conf.dash - update /etc/resolv.conf if changed
r=resolv
cr=/usr/local/bin/cyg-$r.awk
run=/var/run/${r}conf
rrc=$run/$r.conf
SYSCONFDIR=${SYSCONFDIR:-/etc}
conf=$SYSCONFDIR/$r.conf
/bin/mkdir -pv -- $run/ && \
ip=$(/usr/bin/which -- ipconfig) && \
tmp=$(/bin/mktemp -t -- .XXXXXXXX.) && \
$ip /all | $cr > $tmp && \
[ -s $tmp ] && \
[ -w $rrc ] || : > $rrc
if ! /usr/bin/cmp -s -- $tmp $rrc; then
/bin/cp -fv -- $tmp $rrc
/bin/ln -frsTv -- $rrc $conf
fi
/bin/rm -f -- $tmp
More information about the Cygwin
mailing list