Hello,

 

My problem is that curl tries to use ipv6 to resolve DNS entries and my home modem-router doesn't handle ipv6 so curl fails and fallbacks to ipv4. The process lasts 10 to 15 seconds because of this.

 

For example (38s - 23s = 15s to resolve hostname):

 

    $ curl -v --trace-time https://api.owncloud.com
   15:53:23.053958 * Rebuilt URL to: https://api.owncloud.com/
   15:53:23.055233 * Hostname was NOT found in DNS cache
   15:53:38.583565 *   Trying 85.25.74.45...
   15:53:38.803420 * Connected to api.owncloud.com (85.25.74.45) port 443 (#0)

 

And if I add '-4' option (only a few milliseconds):

 

    $ curl -4 -v --trace-time https://api.owncloud.com
   15:54:43.543512 * Rebuilt URL to: https://api.owncloud.com/
   15:54:43.544649 * Hostname was NOT found in DNS cache
   15:54:43.574628 *   Trying 85.25.74.45...
   15:54:43.792575 * Connected to api.owncloud.com (85.25.74.45) port 443 (#0)

 

I try to make curl use ipv4 by default. I changed /etc/gai.conf and uncommented this line:

 

    precedence ::ffff:0:0/96  100

 

But it seems that it is ignored.

 

So I tried to completely disable ipv6 protocol.

 

I added to /etc/sysctl.conf these lines:

 

   net.ipv6.conf.all.disable_ipv6 = 1
   net.ipv6.conf.default.disable_ipv6 = 1
   net.ipv6.conf.lo.disable_ipv6 = 1
   net.ipv6.conf.eth0.disable_ipv6 = 1

 

After reboot, same thing.

 

Then I blacklisted ipv6 in a brand new /etc/modprobe.d/blacklist.conf file:

    blacklist ipv6

 

After reboot, same issue.

 

I deleted all entries in /etc/hosts file relative to ipv6 address.

 

After reboot, same issue.

 

A method consists in disabling ipv6 with /etc/default/grub, but does Armbian uses grub ? update-grub command is not recognized.

 

Though, it seems that ipv6 is really disabled:

 

    $ cat /proc/sys/net/ipv6/conf/all/disable_ipv6
    1

 

    $ man -k ipv6 | egrep gai | wc -l
    0

 

    $ cat /proc/net/if_inet6

    (returns nothing)

 

    $ route -A inet
    Kernel IP routing table
    Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
    default         sagembox.home   0.0.0.0         UG    0      0        0 eth0
    192.168.24.0    *               255.255.255.0   U     0      0        0 eth0

    $ route -A inet6
    Kernel IPv6 routing table
    Destination                    Next Hop                   Flag Met Ref Use If
    ::/0                           ::                         !n   -1  1    63 lo
    ::/0                           ::                         !n   -1  1    63 lo

 

I still have ipv6 connections:

 

    $ netstat -tupvnl | grep -e 'tcp6\|udp6'
    tcp6       0      0 :::41921                :::*                    LISTEN      1575/rpc.mountd
    tcp6       0      0 :::2049                 :::*                    LISTEN      -               
    tcp6       0      0 :::37346                :::*                    LISTEN      1575/rpc.mountd
    tcp6       0      0 :::33253                :::*                    LISTEN      -               
    tcp6       0      0 :::58245                :::*                    LISTEN      1147/rpc.statd  
    tcp6       0      0 :::139                  :::*                    LISTEN      2567/smbd       
    tcp6       0      0 :::111                  :::*                    LISTEN      1119/rpcbind    
    tcp6       0      0 :::44438                :::*                    LISTEN      1575/rpc.mountd
    tcp6       0      0 :::445                  :::*                    LISTEN      2567/smbd       
    udp6       0      0 :::52456                :::*                                1575/rpc.mountd
    udp6       0      0 :::50925                :::*                                1575/rpc.mountd
    udp6       0      0 :::31549                :::*                                1062/dhclient   
    udp6       0      0 :::870                  :::*                                1119/rpcbind    
    udp6       0      0 :::2049                 :::*                                -               
    udp6       0      0 :::39428                :::*                                1147/rpc.statd  
    udp6       0      0 :::111                  :::*                                1119/rpcbind    
    udp6       0      0 :::123                  :::*                                2108/ntpd       
    udp6       0      0 :::42127                :::*                                1575/rpc.mountd
    udp6       0      0 :::42153                :::*                                -

 

I can't find a way to make curl using ipv4 DNS resolving only...

 

Need help...

Why not just using 'alias curl=/usr/bin/curl -4' then?

Why not, I didn't know that. In which file should I write this ?

Is it system wide ?

Does php5-curl calls use this ?

@berturion

If I understood your problem correctly, you already don't have IPv6 address on your network interface, but various application still request both A and AAAA DNS records, and DNS forwarder on your modem/router doesn't handle AAAA requests well.

 

Assuming your router/modem doesn't run OpenWRT now, I would suggest using DNS proxy on your device, i.e. dnsmasq. Configuring it can be a little bit tricky, but in the end is should work.

 

@tkaiser's solution will work, but only for curl.

To be set system wide you could write this to /etc/profile (have a look in there what other files will be read out and where stuff could be defined) 

Thanks for your help.

I added 'alias curl=/usr/bin/curl -4' in /etc/profile, logged out and logged in, but it seems that it is ignored.

I also tried with 'alias curl="/usr/bin/curl -4"', also ignored.

 

Since, my use case is a php-curl call, I am not sure that it can be achieve like that.

 

Dnsmasq was the solution I wanted to avoid because of so much work. But if this is my only option...

Sorry, just checked. dnsmasq is a perfect solution for disabling per-host and per-domain AAAA queries, but there is no option to make it happen for all domains, at least without recompiling it.

 

Since, my use case is a php-curl call, I am not sure that it can be achieve like that.

If php is running as a service, then logging out and back in won't update its environment. 

However, quick googling shows that php-curl has some configurable options:

https://secure.php.net/manual/en/function.curl-setopt.php

Search there for "CURL_IPRESOLVE_V4"

Ok. I re-enabled ipv6 on my machine and simply added these lines to /etc/dhcp/dhclient.conf:

prepend domain-name-servers 79.133.43.124;prepend domain-name-servers 85.25.105.193;

Since then, DNS resolving is done by my local server with opennic nameservers and not my modem-router which fails.

Resolving lasts now 500ms long. Much better.
The real problem was a bad local network configuration. I think my thread isn't so useful.

 

Thanks for your help