EdLAN replacement: next steps

The project to replace EdLAN reached another milestone recently, with the completion of the migration of all subnets away from the old EdLAN core routers across to the new EdLAN distribution routers.  There’s now some tidying-up to be done, and the parts which might affect us in Informatics are scheduled for Tuesday 23rd.

Specifically, some static “summary routes” were added at the beginning of the project, the effect of which were to tell new-EdLAN to send any packets which it didn’t otherwise know how to route to old-EdLAN to be handled there, the intention being to make the migration process as straightforward as possible.  That’s no longer required, so these summary routes now need to be removed.

This affects us in Informatics, because we currently rely on those summary routes to arrange that our traffic to the rest of the University flows smoothly.  Back when we were first arranging the networking for the Informatics Forum we set up OSPF peering with the (old) EdLAN routers to allow us to exchange routing information,  That’s still in place, so our traffic to the rest of the University goes via the old-EdLAN routers.  (We have separate BGP peering with the new-EdLAN routers, and traffic to the rest of the world uses that.)

We can’t just drop our OSPF peering, because the summary routes would still cause traffic to us from the rest of the University to go to the old-EdLAN routers, which would drop it because they wouldn’t know how to get it to us.  Likewise, Information Services can’t just remove the summary routes, because our traffic to the rest of the University would still go out through the old-EdLAN routers, but the return traffic would take a different path, and that asymmetry would cause the University firewalls to drop it.

The plan, which we hope to implement on the 23rd, involves IS adding some temporary static subnet routes, which will be used in place of the summary routes.  They’ll allow IS to remove the summary routes and us to remove our OSPF peering with the old-EdLAN routers, while still keeping our traffic flowing.  Once that’s done, the individual subnet routes will be removed, one by one, while we test to ensure that traffic keeps flowing.

Once all this is done, we’ll be detached from old-EdLAN.  We’ll use OSPF internally within Informatics, and BGP to announce our routes to the new-EdLAN routers.

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