2013/08/06 - Scheduled Maintenance: Proxy Servers
During the Tuesday, August 6th maintenance window, the caching proxy servers that provide access to the web will be replaced, starting at 5.30PM.

This work should not have any noticeable impact on users who make use of the recommended proxy settings. However, as with any change of this nature, there is a risk that our testing has not picked up every conceivable problem. If there's a major issue, you may be unable to browse the web until the problem is resolved.

The proxy servers provide web access, optimise Internet bandwidth, and provide privacy. The current cluster of five proxy servers were installed between 2005-2007, and were due to be replaced some time ago. As a result of the uncertainty around SANReN, this work was postponed several times and is now well overdue.

The existing proxy servers will be replaced with two new ones, each with substantially more capacity than the previous five combined. This involves both physically replacing the servers with newer ones, and using updated versions of the proxy software and operating system. As such, the change is fairly complex and, whilst we've extensively tested the new proxies in isolation, it is not entirely possible to predict what will happen when they're exposed to real traffic.

The new proxy servers will, for the first time, support IPv6 and will prefer the use of IPv6 over IPv4. This may cause unexpected behaviour when trying to access web sites with incorrectly configured IPv6. Our testing shows that the major IPv6-enabled sites (such as Google & Facebook) all work correctly.

This maintenance work is being undertaken in the ITSC-approved scheduled maintenance window, and should be completed before midnight. More information about maintenance windows and maintenance periods.. Note that this is not the only work to be undertaken during this maintenance window.
The currently recommended proxy settings are as follows:

Web browsers that support automatic configuration (IE, Firefox, Chrome, Safari, etc) should be configured to either automatically detect the proxy settings from the network, and/or use the automatic configuration script located at Users who'd prefer us not to do advert blocking (i.e. who wish to see adverts) should disable automatic detection and use as their proxy auto-configuation script.

Software that does not support automatic configuration should be configured to use a proxy address of port 3128. Where possible, sites ending in should bypass the proxy servers. does advert blocking.

No other proxy configurations are supported, and certain configurations may cease to work after this change. Anyone making use of any other proxy settings is strongly advised to update their settings before the scheduled maintenance. Instructions for configuring most major browsers are available at

Note that whilst it is now possible to access many web sites directly and without configuring a proxy, this is neither recommended nor supported. The preferred way to configure a web browser will always be to make use of proxy auto-configuration as above. There are a number of good reasons to make use of the proxy-autoconfiguration script, including:
  • some site-licensed web sites and resources are only accessible via the proxies;
  • by default, the proxies do some degree of advert blocking. This both saves Internet bandwidth (quota!), and provides a more pleasant browsing experience;
  • you benefit from what others are doing -- stuff that's served from the caches is faster, and does not count to quotas;
  • proxies provide a degree of privacy and anonymity on the Internet;
  • the new proxies support IPv6; the Student Network and public labs do not;
  • the proxy auto-configuration scripts are location aware, and optimise settings depending on which part of the network you connect from;
  • using the proxy auto-configuration script allows us to make configuration changes as needed, without requiring you to make changes (for instance, to completely change the proxy servers in this instance);
  • proxy auto-configuration will be required to benefit from any redundant or secondary Internet connection the University purchases.
One of the two new proxy servers is crashing for reasons as yet unknown. We'll continue to try and determine the cause for the duration of the maintenance window, and revert later this evening if necessary. However, this problem will cause intermittent connection failed errors when trying to browse the web.
The cause of the earlier crashes has been identified, and a workaround has been put in place. Since this was done, the new proxies appear to be working stably. However, the normal night-time load on them has significantly decreased as we've got later into the evening, and so this may not be a fair test.

At this stage we cannot rule out rolling back to the previous proxies. We'll monitor them during the course of tomorrow morning (once normal load resumes), and if there's any sign of the problem we saw earlier this evening, we'll make a decision on whether to revert.