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From: tom@wcc.oz.au (Tom Evans)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Setting up a number of Class C Networks - How?
Message-ID: <1816@wcc.oz.au>
Date: 20 Jun 91 01:29:32 GMT
References: <1991Jun13.065802.9433@picasso.cssc-syd.tansu.oz.au>
Organization: Webster Computer Corp, Melbourne, Australia
Lines: 60

In article <1991Jun13.065802.9433@picasso.cssc-syd.tansu.oz.au>, rodney@picasso.cssc-syd.tansu.oz.au (Rodney Campbell) writes:
> We am having a number of problems attempting to set up a number of Class C

I tried to reply by mail, but metro.su.oz has problems and it bounced.
Other responders may be having problems too - you may not get m(any)
replies. So here it is posted.

>Now the problem is that SunOS defaults all of this to a Class B network

The definition of a "default" setting is "As shipped the equipment
will be set up exactly the way you don't want it" :-).

So you have to change it. On all machines. Don't miss any. Don't let
anyone connect new machines onto the network (with the "default"
config) or it may mess up your network.

The Sun Installation manuals probably tell you how to do all this
properly. I'd probably grep for "ifconfig" in /etc/rc*, and change
it there, but what do I know? Address and subnet mask and broadcast too...

>Also the broadcast address on Suns defaults to NET.0 is this right or
>should it be NET.255?

Either is right - as long as it is the same on all machines. Unless
you have something so old on your network that it can't be convinced
to use "NET.255" you should probably use "255".

>      2) Any machine on these nets can talk to any other machine on any
>      other net.

Now it gets interesting. If I read this right you want multiple
separate class c subnets on the same ethernet cable.

Fortunately IP allows this, All good and conforming IP implementations
SHOULD reject all packets not destined to the correct subnet. However,
this is where any "rogue" machines configured wrongly (i.e. configured
as default) may wrongly receive things that they shouldn't, or may ARP
for addresses on the subnet that it isn't on (in which case other
machines won't be able to return packets to it although it can send).

You need to configure an IP router to have multiple LOGICAL IP
interfaces, with different IP addresses, but all connected to the same
physical Ethernet interface. I think Cisco can do this.

>Also if anyone has an Idea about setting up the Webster Multiport Gateway
>to work with this setup?

Set it up as a "normal" IP host with the correct subnetmask and
broadcast address, and let the router connect everything together.

It might be easiest if the router is designated as the "default
router" on all machines - but note that it has a different IP
address on each subnet. You'll probably want all subnets in
/etc/networks, and proper entries in /etc/gateways - not necessary but
it does "document" the network somewhat.

========================
Tom Evans  tom@wcc.oz.au ** ADD ".au" MANUALLY (don't trust "reply") **
Webster Computer Corp P/L, 1270 Ferntree Gully Rd Scoresby, Melbourne 3179
Victoria, Australia 61-3-764-1100  FAX ...764-1179  A.C.N. 004 818 455