SLIP and Dynamic IP

Timothy Mulkey (
Sun, 27 Nov 1994 18:52:21 -0500

This is the third attempt to send this message to the list during the past 3
days (no, there hasn't been any returns or undeliverable messages and I have
been receiving other messages from the list, although from the dates on
messages some of them appear to take serveral days to get through the
listserver). Hopefully, the third time will be a charm. I apologize to anyone
who receives it multiple copies.



>From the current thread of messages from users who are having problems with
CUSM over SLIP lines, I beleive your problem is the dynamic addressing of
the SLIP line IP.

Assigning an alias (hostname) for IP addresses has been standard in the
Internet world since the beginning. Only in the recent past (since the
introduction of bootP servers and the introduction of commercial Internet
providers) there has been an attempt to drop the assignment of aliases for
IP addresses ... I will not comment on the advantages or disadvantages of

Many applications such as Mosaic and gopher are designed to run without an
alias for the host machine; but if you will note, you use the alias of the
server you are contacting in the http of the url. Finger, ping, telnet, and
other applications can also run without the host possessing an alias; but
you contact a server by its IP or its alias.

The Cornell development team have stated several times that they are
planning to remove the requirement for a hostname so please be patient.
Remember, CUSM is beta software; it is still under development and should
NOT be considered to be a software program for the "everyday" user. The
users of CUSM are beta testers of a program which is still under development.

The problem that people are experiencing with CUSM over dynamically
addressed SLIP lines does not appear to be a problem with CUSM. It is a
problem with your SLIP provider (specifically the dynamic addressing IP).

Changing the HOSTS file IP and alias AFTER you have made the SLIP
connection will not provide a solution is you are using the Trumpet Winsock.
Any change in the setup and host file requires that you to restart the
winsock for the changes to be recognized (the configuration file and the
host file are only read when you start tcpman.exe). Restarting the winsock
would log you off the SLIP server and log you back onto the SLIP server ...
there is no guarentee that you will be assigned the same IP when you log
back into the SLIP server.

There are two possible solutions to this problem. The first is to wait
until the CUSM development team has enough time to rewrite the code to
remove the hostname requirement (this may sound simple but remember that the
reflectors to which you connect are UNIX based systems and UNIX systems have
a preference for the alias/hostnames). I do not know how high this change
is on the development team's list of features to implement; from the
messages on the list from the Cornell group, sound for the PC and
compatability with some of the video digitizer boards (such as the QuickCam)
has higher priority.

The second solution is to contact you SLIP service provider. They should
be able to assign aliases for the IP addresses which they use (this involves
registering aliases on DNS; a relatively simple process which many SLIP
providers have already done). You do not have to know what alias is
assigned to a given IP; everything will be "automatic". If your SLIP
provider will not do this, try to get a list of IP addresses which they
dynamically assign. You can then make a host file which lists all possible
IP addresses which you could be assigned with different hostnames for each
IP. No matter what IP you are assigned, a host name will exist in your
HOSTS file. But make sure that you do not have a HOSTS file with
aliases/hostnames assigned for IP addresses if your SLIP provider has
already registered aliases on DNS; this will cause problems with your

One last consideration: Jay Nelson pointed out yesterday that you should
check with your slip provider to make sure that they allow you to access UDP
port 7650 (and port 3456 for Maven). Slip providers can control your access
to certain types of services by blocking your access to specific ports; if
they do not want you to use Mosaic or gopher they can block ports 70 and 80.
Depending upon the type of line (56k, T1, T3) which connects your Internet
service provider to the Internet (not you to your provider), your provider
may have blocked access to certain ports to conserve bandwidth on their link
to Internet (their line has to service you AND the rest of their
subscribers). Again, this is a potential problem with your SLIP provider,
not CUSM.

I hope this is of some help.


Tim Mulkey
Indiana State University