As you’ll be aware by now, EdLAN is changing, though rather more slowly than was originally anticipated for various reasons, and the way that Informatics connects to it has to change too.

Under the old EdLAN, the Informatics network in the central area (Forum, Appleton Tower, Bayes and Wilkie) had a 10Gbps connection to the EdLAN AT router, which carried our “bridged” traffic and most of our “routed” traffic to and from the rest of the University and beyond, and a 1Gbps connection to the EdLAN Old College router, which carried the rest of the “routed” traffic and acted as a hot-spare for the “bridged” traffic.

Under the new EdLAN we now have a 20Gbps connection to the Appeton Tower distribution router carrying “routed” traffic for AT and Wilkie, a separate 20Gbps connection to the AT distribution router which currently carries all of our “bridged” traffic, and a 20Gbps connection to the Forum distribution router which carries our Forum and Bayes “routed” traffic.  There is also a separate 20Gbps connection to the Forum distribution router, intended for “bridged” traffic which is currently mostly idle.

What we now need to do is to transfer the “bridged” traffic originating in the Forum and Bayes, which currently traverses our internal network before making use of our AT connection, so that it uses the Forum “bridged” connection instead.  There are a couple of reasons for this.  The first is that it will make the Forum/Bayes part of our network more independent of the Appleton Tower part of our network, as well as balancing the load across the various links better.

The second reason is that as EdLAN develops, and in particular as the edge roll-out takes place, anticipated to begin later this year, a fast direct path between our Forum core and the EdLAN Forum distribution router for “bridged” traffic will be a necessary part of that transition.

Making the change can’t be done completely transparently, though.  In order to avoid creating forwarding loops, which at 20Gbps would completely break the rest of our network, we need to reconfigure the traffic which is carried on our internal links first before bringing up the new “bridged” connection.  This will cause a break of a few seconds to the Forum traffic which currently transits through Appleton Tower, and in particular wireless and phones.  Only once that has been done will it be safe to patch in the new connection and bring it into service.

We’ll monitor the network after the change, of course, and our configuration system has had some additional constraints added which should mean that loops can’t be set up by accident in future.

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