2.6 Release: Network Topological Mirror Selection

Fri, 13 Feb 2009

MirrorBrain 2.6 has been released, with a major new feature. Through the Apache module mod_asn, it uses BGP routing data to introduce two additional mirror selection criteria: network prefix and autonomous system number (AS). This network-topological knowledge supplements the country-based mirror selection (which relies on the GeoIP database). They work on a pretty much lower level and don't replace the latter. The country lookup is still needed for many requests, because there are many more ASs than mirrors — but for a subpopulation of users the change has a significant impact.

I owe a big "thank you" to Björn Metzdorf who approached me with this idea, nearly a year ago. Also, Christian Deckelmann, Simon Leinen and Marko Jung have provided very fruitful discussion, insight and support.

The change has a number of important implications:

  • It increases the likelihood to select the fastest mirror for a client. (See below.)

  • Traffic from clients of, for instance, a large university network can be sent to their local mirror automatically, with full-featured fallback to external mirrors if the internal one doesn't have what's requested yet. Such a local mirror is highly likely to be the fastest one. This has the potential to save large amounts of needless traffic between organizations.

    Due to the further narrowing on subnet prefix, this works also for huge "hypertrophic" autonomous systems like the German AS680 which contains the majority of the universities.

  • This can be interesting for corporations / organizations which desire to run a mirror and have only their clients sent to it. The point is: the new criteria can effectively be used not only for mirror selection, but also to limit mirror selection to a certain client population, based on network topology. The option to set up a "private" mirror can spare the organization external traffic.

  • And this should be helpful for regions with thin or costly Internet bandwidth, enabling them to establish new mirrors. They can receive normal redirects from MirrorBrain, but have the requests restricted to those from clients in the vicinity of the mirror (same network). Thus, traffic to clients would primarily be local traffic, and the need for outgoing bandwidth would be small compared to what a "traditional" public mirror would have to expect.

    This might hopefully lower the bar to find mirrors in many countries. Please spread the word!

The change is up and running on download.opensuse.org and also on the other MirrorBrain instances.

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