Providing IPv6 DNS resolver data with radvd

One nagging issue I had with IPv6 was how to distribute DNS server addresses and search lists to my clients. It took a little research to find the solution. On IPv4 I had been using DHCP to do this, but DHCP didn’t seem to be the right approach for IPv6. radvd can be used to distribute both types of data. This article covers setup on Ubuntu and OpenWRT. The Ubuntu (Debian) examples below should work with any distribution using/etc/radvd.conf to configure radvd.

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Detecting Email Server Forgery

Most of the spam I received has been sent by servers forging or otherwise obscuring their server identity. RFC2505 states that the server identity and sender address are easily forged. Of these, it is easiest to identify server forgery. Very little, if any, of the personal email has a forged server identity. Unfortunately, legitimate bulk and automated email often show signs of server identity. If you deliver either of these types of emails, this article will provide information on fixing the situation.

The rules here apply to emails originating from the Internet only. Mail User Agents submitting email are expected to violate these rules. MUAs should use an authenticated encrypted connection to the Submission port (576). Relay servers should not apply these rules to connections originating from the local network.

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Securing your Email Reputation with SPF

SPF (Server Policy Framework) is a simple means to limit the ability of others to forge your identity in email. I first implemented it after a forged identity under my domain was used to send Spam. Once SPF was configured,  the bounce messages quickly dropped off.

Although not as frequently implemented as sender address checks, SPF can be used to prevent forgery of the HELO identity. My mail server uses SPF to check the Identity of the server. This is easier to configure and more reliable than checking the domain in the Mail from address. Even though I treat Neutral and Softfail policies as a Fail policy, I have not detected any false negatives. I verify both the address returned by the PTR record for the host and the address in the HELO command. This is primarily because the PTR record is more likely to have a valid domain.

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Setting Up BackupPC on Windows

My original intent in setting up BackupPC was to be able to backup my laptops. They mainly run Windows and have a lot of shared files. Therefore I wanted a backup solution that handled de-duplication. BackupPC was just what I needed. I have already posted an article about Setting Up BackupPC on Ubuntu that includes setting up a server.

This article covers setting up BackupPC on Windows using rsyncd as the protocol. (I tried using Samba, but didn’t like the results with Windows Home editions.) This is done with an extremely minimal cygwin install available from the BackupPC site on SourceForge. The backups described here are not designed for bare metal recovery. They should include all the user’s files and some of the configuration data for installed applications.

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Setting Up BackupPC on Ubuntu

I recently started to do regular backups of all my systems using BackupPC. It uses the rsync protocol to limit the amount of data transferred during backups. Once the initial backup is done, future backups only need to copy incremental changes. This requires far fewer resources than other software I have used

This article covers setting up the server on Ubuntu and configuring backups for Ubuntu and OpenWRT. A future article will cover backing up Windows systems using an rsyncd daemon process.

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Email Logins for Dovecot and Exim

While I was cleaning up my Ubuntu Email server configuration, I consolidated my login security. My SMTP server is Exim and my IMAP server is Dovecot.  Mail User Agents (MUAs) use authentication over TLS encrypted connections to access IMAP and SMTP. Both programs had their own password configuration.

Exim includes Dovecot in its supported authentication mechanisms. This enables one authentication mechanism to be used for both SMTP and IMAP (or POP3). This post also includes configuration details for forced authentication over the Submission port.

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Implementing IPv6 Part 2

We are quickly running out of IPv4 addresses. Are you ready for World IPv6 Day on June 8th, 2011? I have prepared my configuration on OpenWRT and Ubuntu. This includes configuring DNS using bind, email using Exim, and a Squid web proxy.

Having verified that I could establish IPv6 connectivity, I chose to improve my connectivity. This started with getting a tunnel from Hurricane Electric and updating my configuration. I then updated my bind server and Exim mail server support IPv6 addresses. This posting updates and continues from my post on Implementing IPv6 6to4 on OpenWRT.   Review it for information on creating a tunnel and running radvd on OpenWRT.

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Blocking Spam with Exim

Recent reports indicate that spam is increasing again. I have been using Exim to filter spam for several years. Some recent tuning I have done has decreased the percent of spam that reaches my spam filters. This article provides a discussion of the techniques used and provides implementation examples. Spambots tend to be simple programs that don’t handle slow servers very well. Using a greylist is an effective method of blocking them as they usually don’t retry. My latest changes use delays to cause many spambots to abandon their attempt. Greylisting is used only for poorly configured servers that make it to the Recipient command.

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Email Policy actively discourages Spam and email sent from incorrectly configured servers. A legitimate email from correctly configured servers should have little problem being delivered. We believe we are relatively compliant with  RFC 2505 – Anti-Spam Recommendations for SMTP MTAs and other RFCs mentioned at the end of this document.

This article covers our policy implementation for incoming and outgoing email.  These policies apply to all email destined to or originating from,, and other domains for which we may handle email.

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Transparent Squid Proxy

Over the holidays, I had a user experience and attempted browser hijacking. It appeared to have bypassed my squid proxy. My updated configuration now sends all web access via squid. The old firewall rules, that allowed direct access to the Internet, have been replaced with a transparent Squid proxy. This runs on my existing Squid Proxy using another port.

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