Re: PM2-10 w/5-BRI

John Storms (jstorms@livingston.com)
Fri, 13 Sep 1996 09:04:31 -0700

At 04:12 PM 9/11/96 -0700, you wrote:
> I have a PM2-10 with the 5 ISDN module inserted, and have a question
>about routing. I'm about install a Portmaster OR ISDN, at a customers site.
>They've requested 10 IP addresses (1 for the router 9 for the workstations)
>from us, and I don't see it being a problem. The only question I have, is
>do I HAVE to subnet

To receive full functionality, Yes.

>... from what I understand about subnetting I'll loose a
>substantial amount of my measly class 'C'. Does anybody have the same sort
>of thing in place or a suggestion?

The two choices in a situation like this are:
1) Host routing (Yuck!)
2) Subnetting (**heavenly chorus**)

(1) HOST ROUTING:
With host routing you route each ip address over to the remote LAN individually.
PRO:
* Easy, no brainer,
* no subnetting, you don't have to chop your Class C.
CON:
* RADIUS can only have about 8 Framed-Route's which are used to add routes
to the Portmaster when the user connects. This limitation comes from the
limit on the RADIUS packet size.
* Lots of messy routes cluttering your routing table and thus your network
* BIG CON: The remote LAN (with exception of the router) will not be able to
see anything on the host LAN, but will be able to see the Internet.
Since the remote LAN will have the same network address and netmask of your
original network those hosts on the remote network will communicate using
ARP. When the remote LAN tries to communicate to the host LAN it cannot
because it will have no way to distinguish its own LAN from the host LAN and
instead of routing the packets to the host LAN the remote LAN will try
(unsuccessfully) to arp for the host.

(2) SUB-NETTING:
PRO:
* Its really cool and your friends and co-workers will be impressed.
* The remote LAN will be able to see the host LAN
* Less network traffic and smaller routing tables.
CON:
You have to chop the class C.

The closest thing you're going to get to a 10 ip address subnet is a 14 ip
address subnet using a netmask of 255.255.255.240.

Subnet Mask: 255.255.255.240 Hex Mask: 0xfffffff0
Subnet Bits: 28 Host Bits: 4
Number of Subnets: 16 Hosts per Subnet: 14

Network Address IP Range Broadcast Address
.0 .1-.14 .15
.16 .17-.30 .31
.32 .33-.46 .47
.48 .49-.62 .63
.64 .65-.78 .79
.80 .81-.94 .95
.96 .97-.110 .111
.112 .113-.126 .127
.128 .129-.158 .159
.160 .161-.174 .175
.176 .177-.190 .191
.192 .193-.206 .207
.208 .209-.222 .223
.224 .225-.238 .239
.240 .241-.254 .255

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jstorms@livingston.com
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