quick question?

Thu Sep 17 15:23:17 UTC 1998

At 9:42 PM -0600 9/16/98, Kyle D. Smith wrote:
>First of all, i know that this is not the best place to ask this quesiton,
>but it is the only place that can quickly come to mind...
>
>I have a customer who has a block of 62 ip addresses (206.206.162.130 ->
>206.206.162.190 and one for network/brodcast). They are current expanding
>their network, and need around 30 more ip addresses. I went ahead and
>allocated them the following IP address pool (207.66.81.144 ->
>207.66.81.174 with network/brodcast address.) I attempted to use the new
>address on a Apple Macintosh (PowerMac 6500/75) and it erturned an error
>message saying that the router was not on the subnet, and that it could
>not use the new address. I know I should remember how to fix that, but I
>am not sure what to do.... Any help or guidence would be greatly
>appreciated. Thank you very much.
>

For a quick reference, download ftp://ftp.isi.edu/in-notes/rfc1878.txt
This will give you some templates for VLSM subnets.  Here are some relevant
sections:

255.255.255.192 4 nets       N.N.N.0     N.N.N.1-62       N.N.N.63
2 bit Class C   62           N.N.N.64    N.N.N.65-126     N.N.N.127
10 bit Class B               N.N.N.128   N.N.N.129-190    N.N.N.191
                             N.N.N.192   N.N.N.193-254    N.N.N.255

255.255.255.224 8 nets       N.N.N.0     N.N.N.1-30       N.N.N.31
3 bit Class C   30           N.N.N.32    N.N.N.33-62      N.N.N.63
11 bit Class B               N.N.N.64    N.N.N.65-94      N.N.N.95
                             N.N.N.96    N.N.N.97-126     N.N.N.127
                             N.N.N.128   N.N.N.129-158    N.N.N.159
                             N.N.N.160   N.N.N.161-190    N.N.N.191
                             N.N.N.192   N.N.N.193-222    N.N.N.223
                             N.N.N.224   N.N.N.225-254    N.N.N.255

As you see, the first block you assigned is fully in the third /26 range.
The second block, starting with 144, is off somehow. I am a little unclear
if you wanted to give them a /26 or /27 block.

In addition, you need to make sure your router interface is visible on
both subnets.  I'm assuming your configuration is something like this:

                R1
                 |
                 |
    ----------------------------
     with the Macs addressed either in 206.206.162.130
                                    or 207.66.81.144

The router interface needs to have an address in both subnets.  On Cisco,
this is a secondary address, while on Bay, it would be a multinet addresss.

Strategically, encourage your customer to use DHCP address assignment.  If
he does this, you can create a single block on the DHCP server for his
future address needs, and the workstations simply need to reboot to get new
addresses.

As a shameless commercial plug, I have a book on addressing coming out in
November from Macmillan.