Gated

So we have regional and campus networks talking RIP amongthemselves, the NSFnet backbone talking Hello, and the DDN speaking EGP. How do they interoperate? In the beginning there was static routing, assembled into the Fuzzball software configured for each site. The problem with doing static routing in the middle of the network is that it is broadcast to the Internet whether it is usable or not. Therefore, if a net becomes unreachable and you try to get there, dynamic routing will immediately issue a net unreachable to you. Under static

routing the routers would think the net could be reached and would continue trying until the application gave up (in 2 or more minutes). Mark Fedor of Cornell (fedor@devvax.tn.cornell.edu) attempted to solve these problems with a replacement for "routed" called "gated".

"Gated" talks RIP to RIP speaking hosts, EGP to EGP speakers, and Hello to Hello'ers. These speakers frequently all live on one Ethernet, but luckily (or unluckily) cannot understand each others ruminations. In addition, under configuration file control it can filter the conversion. For example, one can produce a configuration saying announce RIP nets via Hello only if they are specified in a list and are reachable by way of a RIP broadcast as well. This means that if a rogue network appears in your local site's RIP space, it won't be passed through to the Hello side of the world. There are also configuration options to do static routing and name trusted gateways.

This may sound like the greatest thing since sliced bread, but there is a catch called metric conversion. You have RIP measuring in hops, Hello measuring in milliseconds, and EGP using arbitrary small numbers. The big questions is how many hops to a millisecond, how many milliseconds in the EGP number 3.... Also, remember that infinity (unreachability) is 16 to RIP, 30000 or so to Hello, and 8 to the DDN with EGP. Getting all these metrics to work well together is no small feat. If done incorrectly and you translate an RIP of 16 into an EGP of 6, everyone in the ARPAnet will still think your gateway can reach the unreachable and will send every packet in the world your way. For these reasons, Mark requests that you consult closely with him when configuring and using "gated".