Linux IPv6 HOWTO (en)
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# 4.5. IPv6-ready client programs (selection)

To run the following shown tests, it's required that your system is IPv6 enabled, and some examples show addresses which only can be reached if a connection to the 6bone is available.

## 4.5.1. Checking DNS for resolving IPv6 addresses

Because of security updates in the last years every Domain Name System (DNS) server should run newer software which already understands the (intermediate) IPv6 address-type AAAA (the newer one named A6 isn't still common at the moment because only supported using BIND9 and newer and also the non-existent support of root domain IP6.ARPA). A simple test whether the used system can resolve IPv6 addresses is

    # host -t AAAA www.join.uni-muenster.de

and should show something like following:

    www.join.uni-muenster.de. is an alias for tolot.join.uni-muenster.de.
    tolot.join.uni-muenster.de. has AAAA address
    ¬ 2001:638:500:101:2e0:81ff:fe24:37c6

## 4.5.2. IPv6-ready telnet clients

IPv6-ready telnet clients are available. A simple test can be done with

    $ telnet 3ffe:400:100::1 80
    Trying 3ffe:400:100::1...
    Connected to 3ffe:400:100::1.
    Escape character is '^]'.
    HEAD / HTTP/1.0

    HTTP/1.1 200 OK
    Date: Sun, 16 Dec 2001 16:07:21
    GMT Server: Apache/2.0.28 (Unix)
    Last-Modified: Wed, 01 Aug 2001 21:34:42 GMT
    ETag: "3f02-a4d-b1b3e080"
    Accept-Ranges: bytes
    Content-Length: 2637
    Connection: close
    Content-Type: text/html; charset=ISO-8859-1

    Connection closed by foreign host.

If the telnet client don't understand the IPv6 address and says something like “cannot resolve hostname”, then it's not IPv6-enabled.

## 4.5.3. IPv6-ready ssh clients

### 4.5.3.1. openssh

Current versions of openssh are IPv6-ready. Depending on configuring before compiling it has two behavior.

- --without-ipv4-default: the client tries an IPv6 connect first automatically and fall back to IPv4 if not working

- --with-ipv4-default: default connection is IPv4, IPv6 connection must be force like following example shows

    $ ssh -6 ::1
    user@::1's password: ******
    [user@ipv6host user]$

If your ssh client doesn't understand the option “-6” then it's not IPv6-enabled, like most ssh version 1 packages.

### 4.5.3.2. ssh.com

SSH.com's SSH client and server is also IPv6 aware now and is free for all Linux and FreeBSD machine regardless if used for personal or commercial use.

## 4.5.4. IPv6-ready web browsers

A current status of IPv6 enabled web browsers is available at IPv6+Linux-status-apps.html#HTTP.

Most of them have unresolved problems at the moment

1. If using an IPv4 only proxy in the settings, IPv6 requests will be sent to the proxy, but the proxy will fail to understand the request and the request fails. Solution: update proxy software (see later).

2. Automatic proxy settings (*.pac) cannot be extended to handle IPv6 requests differently (e.g. don't use proxy) because of their nature (written in Java-script and well hard coded in source like to be seen in Maxilla source code).

Also older versions don't understand an URL with IPv6 encoded addresses like http://[2001:a60:9002:1::186:6]/ (this given URL only works with an IPv6-enabled browser!).

A short test is to try shown URL with a given browser and using no proxy.

### 4.5.4.1. URLs for testing

A good starting point for browsing using IPv6 is http://www.kame.net/. If the turtle on this page is animated, the connection is via IPv6, otherwise the turtle is static.

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