Re: tcp-ip terminal servers

Lars J Poulsen (lars@ACC-SB-UNIX.ARPA)
Mon, 31 Oct 88 08:40:58 PST

> Date: 27 Oct 88 06:22:53 GMT
> From: suned1! (Everett F. Batey II)
> Organization: NSWSES, Port Hueneme, CA
> Subject: Re: tcp-ip terminal servers
> References: <337@thor.wright.EDU>, <>, <417@wasatch.UUCP>
> MY QUESTION. We are on a site with a 192... address assigned. That is across
> a MILnet gateway. To use my telnet / rlogin servers, must I consume some of
> those 254 addresses?

A terminal server is a HOST, albeit a somewhat specialized one (i.e. it does
perform all kinds of host services). A host must have an IP address.
If your ethernet has a network number, the host must have an address
with the address space of that network.

Why would you (a) not want that ?
              (b) think this could be otherwise ?

> Is there a network legal way to be on another net number
> in the 255.255.255. upper 24 bits? Which my local hosts can see and still
> get helped NS from my local domain internal name server?

A terminal server does not have to be on the same network as the hosts
it is communicating with. I.e. if your terminal server is on an ethernet
connected to Milnet with a proper gateway, it can communicate with any
host on the combined Internet, i.e. not just with your local machines
but with any machines attached to MILnet, any machines attached to
ARPAnet, any machines attached to NSFnet, any machines attached to
the MIT campus net, etc. This is why we have IP in the first place.

Thus, if you have multiple networks, you can attach terminal servers
to whichever network you want, and they will still get to wherever
you want to get to.

However, it is a feature of IP routing, that when your packets move from
one net to another, they do so at an IP gateway. Thus, you are imposing
a processing load on the gateway node. This is not altogether desirable
if the reason you moved the terminal ports off the bigger host in the
first place was to save processing cycles on the bigger host.

The location of your terminal server with respect to the name server
is a slightly different issue. If the terminal server uses standard
DOMAIN protocol, this runs on top of IP, so you can get name service
from any host on the combined internet that has access to the information
for your domain; however, you will usually (for reasons of performance
and overhead avoidance) want to get it from a host as close to the terminal
server as possible.

> WHAT does every one else with multiple hosts and servers on a local ethernet
> gatewayed to ARPA / Internet do to preserve host addresses with servers?
> ...
> efb@elroy.JPL.Nasa.Gov sun!tsunami!suned1!efb

Numbers are fairly cheap. If you are planning to connect more than 254 hosts
(including PCs an terminal servers) to your local network, then you should
get a class B network instead of a class C network. This is MUCH friendlier
to the world than to have multiple class C networks behind a gateway.

        / Lars Poulsen
          ACC Customer Service
          Advanced Computer Communications

        ("We make advanced computers communicate")

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