nd: message containing all or part of its routing table* 3 - traceon: Obsolete. Ignore these messages* 4 - traceoff: Obsolete. Ignore these messages* 5 - reserved: Used by Sun MicrosystemsThe rest of the datagram consists of a list of destination with information about each. The maximum size of the datagram is 512 octets.PROTOCOL LIMITATIONS:There are a number of limitations of the protocol. It is limited to networks with no more than 15 hops as its longest path. This is to limit the use to moderate sized networks.Gateways and lines fail and come back up. To handle this we need to update the routes and distribute it throughout the network. The process of establishing routes is called convergence. Propagation of routing through the network takes time, so convergence doesn't happen instantaneously. "Counting to infinity" is a method to help speed-up the convergence of the network. This comes into play when the network system consists of several hundred networks, in which a routing table would involve all of them. The concern is that it would take too much bandwidth and time to build the routing table. This is a concern only for slow lines.Split horizons derive from the premise that it is never useful to send information about a route back in the direction from which it came. The following illustrates the split-horizon rule:N1 ---- R1 ---- N2 ---- R2 -----Where: R1 & R2 are routers N1 & N2 are networksRouter 1 (R1) initially broadcasts that it has a route to Network 1 (N1). There is no reason for Router 2 (R2) to include this route in its update back to R1 because R1 is closer to N1. The split-horizon rule says that R2 should exclude this route from any updates it sends to R1. The split-horizon rule helps prevent routing loops. Consider, for example, the case where R1's connection to N1 goes down. R2 continues to inform R1 that it can get to N1 (through R1). If R1 does not have sufficient intelligence, it actuall...
