Cover V03, I03


Questions and Answers

Bjorn Satdeva


The UniForum trade show took place in San Francisco, March 21th to 25th. Because of the size of the show, it is impossible to visit every stand on the show floor. This year I had decided to look for system administration tools designed to provide overall, site-wide support to the system administration team -- what the marketing people like to call enterprise system management.

General System Administration Tools

So far I have found only two products, both of which have been around for some time, that actually qualify for this category: Tivoli Systems and Computer Associates' CA-Unicenter. The Tivoli demonstration was very surprising to me, but not in the good sense of the word. Like most of the other vendors, they had a small circus going on in one corner of the stand, giving what was supposed to be a technical demonstration. However, in the best tradition of such marketing shows, that presentation did not have much technical content. I was surprised to learn that the user administration package, which made up the original base of the product, is still presented as an important feature. In my experience, user administration has never been a significant part of the total system administration work load.

I had quite a bit of difficulty finding someone who could provide a more in-depth demonstration of the system (I had to return three times), but after seeing the demonstration, I felt that there was good reason for this, as the product seems to me to have very little of practical value implemented at this time. The exception to this is their file distribution system, which is implemented using a subscription-oriented strategy. While it will not solve all file distribution problems, I know of no other product which solves this specific kind of file distribution problem (which is not an easy one to solve). However, overall, the current product does not have much appeal to me, as it appears not to provide enough benefits to justify the complication of supporting a new product.

The second product is Computer Associates' UniCenter. This is actually an existing product which was originally written for the mainframe environment and later ported to UNIX. When I first encountered the UniCenter, it seemed that everybody involved with the product believed that what was good for the business-oriented mainframe would be good for the rest of the world. What I saw at UniForum convinced me that the people behind UniCenter have since learned that much of the UNIX world is different because of the very large installed base of systems used for scientific and engineering applications. For such installations, many of the solutions in the original UniCenter were aimed at nonexistent problems. Now, however, UniCenter has evolved in a direction where it can provide a useful contribution to the system administration team, whether the site is business or scientific/engineering oriented.

In comparing the two products, I believe that UniCenter may soon arrive, while Tivoli is still more of a promise than an actuality. If I were to install either product, I would most certainly require the vendor to allow for an extended evaluation period, during which the product could be tested on my machines by my administrators, to see if it would deliver as promised. As part of the evaluation, I would take into account the fact that Computer Associates certainly has the financial muscle to develop a good product. Whether either company has the vision to develop a truly efficient system administration tool that can be used to administer a large number of hosts in a networked environment still remains to be seen.

Bellcore Pingware

One of the fun things at a show like UniForum is to visit the small, inexpensive booths located at the edge of the show floor. It is very often here that you will find the new and exciting technology, which will make the headlines in the future. However, this year, I did not see anything of particular interest for us system administrators, as the main topic seemed to be object-oriented technology.

At the Bellcore booth I did find one completely new product which looked interesting -- a security analysis tool called Pingware. This tool is designed to scan a network for connected systems, make a security audit of each system, and create a report on system vulnerabilities. It appears to be a useful and much needed tool for legitimate use by system administrators, but can also be abused by crackers. When I asked about this very touchy and controversial issue, I got the impression that the company is struggling, as so many of us are, to come to a reasonable and balanced solution. I think it is very good that the UNIX community is finally moving away from the old paradigm of not disclosing security vulnerabilities, even though the process of disclosure is painful because we do not yet have any good idea of how this should be done. The black hats have had this kind of information easily available for for years; only by also making it available to the people who have a legitimate use for it will we be able to establish any kind of reasonable balance.

To BSDI or Not to BSDI

One last thing: I had very much looked forward to this year's UniForum conference as an opportunity to ask the vendors of UNIX SVr4 for the PC platform about their thoughts on the resolution of AT&T's lawsuit against BSDI (the suit was settled out of court, and the case was sealed, but as BSDI is still in business, it is a fairly good guess that they, from a practical point of view, won the case). At UniForum in 1991, when the suit had just been filed, several PC UNIX vendors present at UniForum stated that the BSDI version of UNIX with full source code was no threat to them, as the lawsuit would put BSDI out of business within months. I had therefore planned to ask the the same question again, but to my disappointment, none of those vendors were present.


The Third Conference for System Administration, Networking and Security took place in Washington, D.C. in the first week of April. The conference was highly successful, doubling the number of attendees from last year. It has been very interesting to watch this conference from year to year, as it matures. While it is very different from the LISA conference, which traditionally takes place in the fall, somewhere on the West Coast, it appears to be following the same pattern, with respect both to the increasing quality of the papers presented and the increasing number of attendees. However, while LISA tends to focus on the leading edge of UNIX system administration methods and technology, SANS focuses on the practical usability of the tools and methods presented. And while LISA is oriented towards scientific and engineering sites, SANS has a slant towards the administration of UNIX in a business environment.

It is not possible to describe all the papers in this space, but to give a taste of the conference, I will outline some of them briefly. Marcus Ranum's "A Network Perimeter with Secure External Access" describes an overall strategy for protecting systems from various outside threats. Once again Marcus has successfully treated a very fuzzy topic in a systematic manner. Gene H. Kim and Eugene H. Spafford wrote of practical experiences with tripwire in the paper "Experiences with Tripwire: Using Integrity Checkers for Intrusion Detection." Michael Neuman and Gary Christoph described a special shell providing restricted root access. Hal Pomeranz presented a re-implementation of Paul Anderson's disk caching as a simple but effective method of reducing NFS traffic in "A New Network for the Cost of SCCI Cable"; and Michele D. Crabb outlined an overall strategy used at Ames Research Center in her "Guarding the Fortress, Efficient Methods to Monitor Security on 300 Systems." I also want to mention Matt Bishop's talk on common security problems and Dan Geer's talk on security breaches in some commercial sites he had experienced. Unfortunately, neither talk was accompanied by a paper.

The Proceedings from the SANS III conference are available from USENIX, 2560 Ninth St., Ste. 215, Berkeley, CA 94710, (510) 528-8649.

A Few Updates

Before going on to this issue's questions, there are a few items of old business that need to be taken care of.

In the January issue, the explanation of how to do subnetting contained an unfortunate mistake. The correct address for the common network mask is

With respect to the same column, I have been asked if I know of a program which can calculate the various address which must be specified when using subnets. I do not know of any, but if any reader knows of one (or has written one), I will publish it here. I usually use the UNIX utility bc (for Board Calculator). Its ability to convert between base 10 and base 16 makes it adequate, but not necessarily a user-friendly tool for this purpose.

Again on the same subject, a few readers have asked how using netmasks in class B addresses differs from class C. In principle, there is no difference. In each case, the network address part is expanded at the cost of the size of the host's address. The only practical difference is the starting point of where the IP-address is split between network address and host address.

One reader pointed out that with a router which supports separate subnet masks for each interface, it is possible to use different subnet masks on different subnets. I didn't mention this because I wanted to keep a topic which is generally considered to be very confusing as simple as possible.

Finally, I have gotten a number of reminders about RFC 1219, "On the Assignment of Subnet Numbers." The RFC is always a good place to search for information, and I agree with this. However, the purpose of the column was to explain how subnets work, and given the limited space available, I sometimes have to eliminate material that would certainly be included were I covering the same topic in a book. This is an unfortunate fact of life.

Several readers noted that the Trojan horse example described in the March issue will not work on all systems. I hinted at that in the discussion. My goal was not to provide a portable Trojan horse, but rather to give a good explanation of why it is a very bad idea to have the current directory in the search path. I believe I made made my point and rest my case.

 Q [Note: This question has been paraphrased from a very long and very specific one.] Your description of subnets was very useful to us. However, we have three class C addresses here, and two subdomains. How do I manage to split the name server between the various subdomains?

 A I can understand why this question has arisen, as the use of IP-addresses in networks and the name server seems similar. However, while subdomains and subnets may seem similar, they are very different, and should not be confused. named does not understand subnets, and with good reason: it is not a network management tool, but rather an information server, used to map hostnames to IP addresses or the reverse thereof. Unfortunately, this doesn't make it any easier to administer the subnet and subdomains in a reasonable manner. The way I would solve this specific problem would be to specify both the host name and the subdomain for each entry in the name server configuration files. This will work, as long as both subdomains are served by one primary name server.

 Q You have in the past mentioned two software packages which can be used to implement a firewall, SOCKS and the Firewall Tool Kit. Which of the two is the best?

 A It depends on your site and its users. Both packages implement what is usually called a proxy service. SOCKS, the older of the two packages, requires that the client software (for example ftp) be replaced on all inside hosts with a version that understands the SOCKS protocol, which is used to connect to the firewall, which in turn makes the connection to the desired host on the Internet. I believe that SOCKS is the first publicly available software to have implemented this kind of service, and it has worked very well for a number of sites. However, because it requires replacement of the client, it will not work well at sites where a large number of PCs or MacIntoshes are used, as there are no clients available for those machines (at least not that I know of). In comparison, the Firewall Tool Kit is only installed on the firewall; all systems on the inside use their usual clients for ftp or telnet. However, the Firewall Tool Kit is not transparent to users, as it requires them to type slightly different commands than those they would otherwise use. It is of course possible to replace the inside clients which interact with the toolkit, to make this change invisible, but you then have the same software distribution problem you have with SOCKS.

In my opinion, the Firewall Tool Kit is the better of the two packages, as it not only implements a needed service, but does so in a well thought out and very secure manner. In fact, our firewall was originally implemented with SOCKS, but we've redone it with the Firewall Tool Kit, due to what I think is a better design. The Firewall Tool Kit also has the advantage of being able to build on the experiences gained from SOCKS. On the other hand, SOCKS provides support for the very popular Mosaic program, which is not supported by the Firewall Tool Kit. A major negative for SOCKS, however, is that it has recently been used by intruders to open up connections from the outside (pretty ironic, that the very tools which should protect our systems are used to penetrate them). If you are using SOCKS, at least be very sure to run the very latest version of sendmail.

 Q In your Q&A in the March/April 1994 issue of Sys Admin, you answered a question regarding using rdump to a remote tape host without enabling root access from that host. I tried to set this up on my systems, but it did not work. I created an account "operator" on system_1 and gave it Group ID sys so that it would have read access to the disk devices (which are UID root and GID sys on these systems). I created the same account on the tape host: system_2. I can execute any number of remsh <command> type of commands from system_1 to system_2, but rdump fails with a message: "rresvport: bind: Permission Denied." Apparently, only super-user can obtain a socket with a privileged address bound to it. I do not know of any way around this limitation in using rdump, without being root, that is. Do you?

 A Check to see if the dump program is SUID root (some vendors ship it without this). Your conclusion -- that you need to be root in order to access a socket below port 1024 is correct -- which is why it is necessary to make dump and rdump (which are actually the same program, with a link) SUID root. This is less of a problem than opening up general root access between the systems.

About the Author

Bjorn Satdeva is the president of /sys/admin, inc., a consulting firm which specializes in large installation system administration. Bjorn is also co-founder and former president of Bay-LISA, a San Francisco Bay Area user's group for system administrators of large sites. Bjorn can be contacted at /sys/admin, inc., 2787 Moorpark Ave., San Jose, CA 95128; electronically at; or by phone at (408) 241-3111.