# What are Some Popular Networks?

Over the last 25 years or so, a number of networks and network protocols have been defined and used. We're going to look at two of these networks, both of which are public'' networks. Anyone can connect to either of these networks, or they can use types of networks to connect their ownÂ hostsÂ (computers) together, without connecting to the public networks. Each type takes a very different approach to providing network services.

UUCP

UUCPÂ (Unix-to-Unix CoPy) was originally developed to connect Unix (surprise!) hosts together. UUCP has since been ported to many different architectures, including PCs, Macs, Amigas, Apple IIs, VMS hosts, everything else you can name, and even some things you can't. Additionally, a number of systems have been developed around the same principles as UUCP.

BATCH-ORIENTED PROCESSING.

UUCP and similar systems areÂ batch-orientedÂ systems: everything that they have to do is added to a queue, and then at some specified time, everything in the queue is processed.

## Implementation Environment

UUCP networks are commonly built using dial-up (modem) connections. This doesn't have to be the case though: UUCP can be used over any sort of connection between two computers, including an Internet connection.
Building a UUCP network is a simple matter of configuring two hosts to recognize each other, and know how to get in touch with each other. Adding on to the network is simple; if hosts called A and B have a UUCP network between them, and C would like to join the network, then it must be configured to talk to A and/or B. Naturally, anything that C talks to must be made aware of C's existence before any connections will work. Now, to connect D to the network, a connection must be established with at least one of the hosts on the network, and so on. Figure shows a sample UUCP network.

A Sample UUCP Network

In a UUCP network, users are identified in the format
host!userid. The !'' character (pronounced "bang'' in networking circles) is used to separate hosts and users. A bangpath is a string of host(s) and a userid likeA!cmcurtin or C!B!A!cmcurtin. If I am a user on host A and you are a user on host E, I might be known as A!cmcurtin and you as E!you. Because there is no direct link between your host (E) and mine (A), in order for us to communicate, we need to do so through a host (or hosts!) that has connectivity to both E and A. In our sample network, C has the connectivity we need. So, to send me a file, or piece of email, you would address it to C!A!cmcurtin. Or, if you feel like taking the long way around, you can address me as C!B!A!cmcurtin.

The "public'' UUCP network is simply a huge worldwide network of hosts connected to each other.

## Popularity

The public UUCP network has been shrinking in size over the years, with the rise of the availability of inexpensive Internet connections. Additionally, since UUCP connections are typically made hourly, daily, or weekly, there is a fair bit of delay in getting data from one user on a UUCP network to a user on the other end of the network. UUCP isn't very flexible, as it's used for simply copying files (which can be netnews, email, documents, etc.) Interactive protocols (that make applications such as the World Wide Web possible) have become much more the norm, and are preferred in most cases.

However, there are still many people whose needs for email and netnews are served quite well by UUCP, and its integration into the Internet has greatly reduced the amount of cumbersome addressing that had to be accomplished in times past.

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## Security

UUCP, like any other application, has security tradeoffs. Some strong points for its security is that it is fairly limited in what it can do, and it's therefore more difficult to trick into doing something it shouldn't; it's been around a long time, and most its bugs have been discovered, analyzed, and fixed; and because UUCP networks are made up of occasional connections to other hosts, it isn't possible for someone on host E to directly make contact with host B, and take advantage of that connection to do something naughty.

On the other hand, UUCP typically works by having a system-wide UUCP user account and password. Any system that has a UUCP connection with another must know the appropriate password for the
uucp or nuucpaccount. Identifying a host beyond that point has traditionally been little more than a matter of trusting that the host is who it claims to be, and that a connection is allowed at that time. More recently, there has been an additional layer of authentication, whereby both hosts must have the same sequence number , that is a number that is incremented each time a connection is made.

Hence, if I run host B, I know the uucp password on host A. If, though, I want to impersonate host C, I'll need to connect, identify myself as C, hope that I've done so at a time that A will allow it, and try to guess the correct sequence number for the session. While this might not be a trivial attack, it isn't considered very secure.