Welcome IPv4 user

Email via IPv6 on cPanel

Both the Courier and Dovecot mailservers can be used with cPanel to provide users with POP3 or IMAP access to their mail.

Many older cPanel installations will be running Courier. Interestingly Courier's default config already has IPv6 enabled by default. IPv4 addresses in log files are written in IPv6 compatible format by prepeding them with "::ffff:".

In order to connect to your mail server via IPv6 you can open your favourite mail client (Thunderbird is known to work) and set the server name to your servers IPv6 address. View the log files at "/var/log/maillog" to see your client login via IPv6.

Next step would be to add a DNS entry for your mail server. If you are the only user on your mail domain then you can add the IPv6 address of your server as a AAAA record for mail.yourdomain.co.za. If you have many other users on your domain then you may want to rather add the AAAA for mail6.yourdomain.co.za. Users with broken IPv6 connectivity may experience higher latency or inability to connect if the AAAA is applied directly to the 'mail' hostname.

Dovecot requires one change to enable IPv6: the listen directive needs to be adjusted to include both IPv4 and IPv6. Access the dovecot config template and add the line "listen = *, [::]" and rebuild the config. This should make dovecot IPv6 capable but this has not been tested.


An IPv6 enabled cPanel server

This is the first in a series of posts about getting cPanel ready for IPv6. The developers of cPanel have claimed that IPv6 is on their roadmap but have as yet not even released an ALPHA with IPv6 capabilities. This is surprising since almost all the underlying services that that cPanel manages already have IPv6 support and many of them are trivial to activate.

cPanel uses bind under the hood to provide DNS. Bind has mature IPv6 support and is the ideal candidate for getting going with a dual-stack cPanel environment.

cPanel is capable of loading AAAA DNS records into DNS zones. These AAAA records are the primary IPv6 DNS records for mapping a hostname to an IPv6 address. This can be done via the 'Edit DNS zone' feature that is available in the WebHost Manager but is not available on the simple DNS editor in the cPanel interface.

Serving AAAA responses is one thing but you also want your DNS server to communicate on IPv6. The first step is to make sure that your server has IPv6 connectivity. This can be checked by loging in via ssh and running the command 'ping6 ipv6.google.com'. Once you are happy that you have a working IPv6 connection you can proceed to the next step:

This step requires that you are the root user on the server. You need to open the file '/etc/named.conf' in your favourite terminal text editor. You then need to add the line

listen-on-v6 { any; };

after the line

options {

You can then save the file and restart the nameserver via the web interface. If all goes well your server will be answering IPv6 DNS queries.

You can test this firstly by doing a 'dig www.mydomain.com @::1' where ::1 is the IPv6 equivalent of localhost. If that works correctly then you want to test a DNS query from another IPv6 enabled host. You know have IPv6 capable DNS servers.


One year to go

It passed by without any fanfare. I don't think anyone even noticed.

According to Geoff Huston's mathematical modeling we are now less than one year away from the final depletion of IANA's pool of free IPv4 netblocks.

The current estimate is that this will happen on 10th July 2011. What is going to happen you might ask...

An agreement was reached in the Internet community that as soon as the IANA has only 5 '/8' prefixes remaining in their pool they will all be handed out in one go. One prefix each to the 5 Regional Internet Registries (RIR). The registries are then responsible for distributing those addresses to users in their region.

Most RIRs have put in place policies that limit the maximum allocation size and rate of consumption of the final '/8'. This is intended to prevent a run-on-the-bank type situation and also try and ensure that small blocks of IPv4 addresses are available for critical systems such as DNS for a while.

The reality is that after July next year you are unlikely to be able to get an IPv4 allocation from your local RIR that will be big enough to build an ISP.

Are you ready for that?


IPv6 Spam

I sometimes have mixed feelings for spammers. While I mostly despise them for the time and money they waste in my life - I can't help being a little impressed every now and again.

There has thus far not been any noticeable email spam hitting my mail server on its IPv6 address. This is a relief since the availability of IPv6 RBLs and other spam fighting filters is currently limited.

I was however privileged to receive my first IPv6 comment spam on this blog recently. This means that one of the botnet herders has either included IPv6 support in their code or they are writing good enough code that it is IP version agnostic. Is this a good thing...?

I had hoped that the IPv6 Internet would be free of the evils of the IPv4 Internet. As long as it stays niche there will be no reason for the worst netizens to show their faces on this side of the great IP divide. Then of course we would not be achieving our end goal of moving everyone (including the spammers) to IPv6.


Where does that IP come from?

Due to the size of the IPv6 address space it has been possible to reserve large blocks of addresses for specific purposes and reduce the fragmentation of IP blocks considerably. This leads us to be able to quite easily identify the IPv6 addresses which appear in log files and connection lists:

  • 2001:0:* - This block of addresses is assigned to the Teredo protocol. This tunneling protocol is installed by default on Windows Vista and Windows7 operating systems. It is used by hosts behind NAT gateways to reach IPv6 hosts. Teredo is NOT preferred over IPv4 and will only generally be used when a suitable IPv4 connection can't be made. Teredo is quite popular with torrent clients to reach hosts behind a NAT.
  • 2001:200-A000:* - The first global address allocations were made out of this range of prefixes. Typically these are early adopter networks and many of the major tunnel brokers have prefixes in this range.
  • 2002:* - The 6to4 protocol was assigned this prefix. The 8 digits following the initial sequence are a hexadecimal representation of the public IPv4 address that defines the end of the tunnel. 6to4 thus only functions if the tunnel endpoint is a public IP. In the past 6to4 has been popular for providing IPv6 along side IPv4 on residential gateway/router devices.
  • 240*: - Range that was issued to APNIC for users in the Asia and Pacific regions.
  • 260*: - Range that was issued to ARIN for users in the North American region.
  • 280*: - Range that was issued to LACNIC for user in the Latin American region.
  • 2A0*: - Range that was issued to RIPE NCC for user in the European region.
  • 2C0*: - Range that was issued to AfriNIC for user in the African region.