Ed Krol

“ One word of warning, it is only with extreme caution that one should use static routes in the middle of a network which is also using dynamic routing. The routers passing dynamic information are sometimes confused by conflicting dynamic and static routes. If your host is on an ethernet with multiple routers to other networks on it and the routers are doing dynamic routing among themselves, it is usually better to take part in the dynamic routing than to use static routes. ”

“ It is probably the most reliable, easiest to implement, and least likely to get one into trouble for a small network or a leaf on the Internet. This is, also, the only method available on some CPU-operating system combinations. If a host is connected to an Ethernet which has only one gateway off of it, one should make that the default gateway for the host and do no other routing. ”

“ If a router connects connects two net- works directly, a machine on the other side of the router is one hop away.... As the routing information is passed through a gateway, the gateway adds one to the hop counts to keep them consistent across the net- work. The diameter of a network is defined as the largest hop-count possible within a network. ”

“ The NIC is a facility available to all Internet users which provides information to the community. There are three means of NIC contact: network, telephone, and mail. The network accesses are the most prevalent. Interactive access is frequently used to do queries of NIC service overviews, look up user and host names, and scan lists of NIC documents. ”

“ RIP RIP is a routing protocol based on XNS (Xerox Network System) adapted for IP networks. It is used by many routers (Proteon, cisco, UB...) and many BSD Unix systems BSD systems typically run a program called "routed" to exchange information with other systems running RIP. RIP works best for nets of small diameter where the links are of equal speed. The reason for this is that the metric used to determine which path is best is the hop-count. A hop is a traversal across a gateway. So, all machines on the same Ethernet are zero hops away. ”

“ These inconsistencies can cause circular routes (called routing loops) where once a packet enters it is routed in a closed path until its time to live (TTL) field expires and it is discarded.
Other algorithms may know about only a subset of the network. To prevent loops in these protocols, they are usually used in a hierarchical network. They know completely about their own area, but to leave that area they go to one particular place (the default gateway) . Typically these are used in smaller networks (campus, regional...) ”

“ If you consider the problem of measuring delay on a link for the metric, you find that it is not an easy thing to do. You cannot measure round trip time since the return link may be more congested, of a different speed, or even not there. It is not really feasible for each node on the network to have a builtin WWV (nationwide radio time standard) receiver. So, you must design an algorithm to pass around time between nodes over the network links where the delay in transmission can only be approximated. ”

“ The only requirements are that the requestor have two machines reachable from the Internet, which will act as name servers for that domain. Those servers could also act as servers for subdomains or other servers could be designated as such. Note that the servers need not be located in any particular place, as long as they are reach- able for name resolution. (U of I could ask Michigan State to act on its behalf and that would be fine) . The biggest problem is that someone must do maintenance on the database. If the machine is not convenient, that might not be done in a timely fashion. ”

“ Many times in larger networks where various parts of the network are under different administrative controls, you would like to pass on through RIP only nets which you receive from RIP and you know are reasonable. This prevents people from adding IP addresses to the network which may be illegal and you being responsible for passing them on to the Internet. ”

“ There are two ways in which a campus could spread the news and not cause these messages to inundate the wide area networks. One is to re-reflect the message on the campus. That is, set up a reflector on a local machine which forwards the message to a campus distribution list. The other is to create an alias on a campus machine which places the messages into a notesfile on the topic. Campus users who want the information could access the notesfile and see the messages that have been sent since their last access. ”

“ Congestion can be viewed as a decrease in the efficacy of a link. So, as a link gets more congested, RIP will still know it is the best hop-count route and congest it even more by throwing more packets on the queue for that link. ”

“ In addition, they all should have some knowledge of what is happening to the Internet in total. If a problem comes up, it is suggested that a campus network liaison should contact the network operator to which he is directly connected. ”

“ For people without network access, or if the number of documents is large, many of the NIC documents are available in printed form for a small charge. One frequently ordered document for starting sites is a compendium of major RFCs. Telephone access is used primarily for questions or problems with network access. (See appendix B for mail/telephone contact numbers) . ”

“ It is available by using
%telnet sri-nic.arpa
on a BSD system and following the directions provided by a user friendly prompter. From poking around in the databases provided one might decide that a document named NETINFO:NUG.DOC (The Users Guide to the ARPAnet) would be worth having. It could be retrieved via an anonymous FTP. An anonymous FTP would proceed something like the following. (The dialogue may vary slightly depending on the implementation of FTP you are using) . ”