Server assigned netmask 255.255.255.255

Hello all,

I have one question I can't answer for a long time. I am sure here I can find my answer

I have 3COM Netserver16 (simple router with 16 built in modems), I use it for leased line connections for my customers. The configuration to be done is very simple so I'll just mention interesting part:

set user test address 192.168.0.1
set user test netmask 255.255.255.255

I tried to find out what does netmask 255.255.255.255 mean (when setting up firewall this netmask means the exact host) but how this works in networking means? It should mean that network address, host address and broadcast address are the same. This is different case and I haven't found any docs about it's logics so maybe someone can point me. One more thing: If I define route like

192.168.0.0 255.255.255.240 <ip of my netserver>

then I have to assign 192.168.0.0/32 address to my user. Is this valid address/mask for standalone host?

Thanks in advance.

Wrath_child,

Good question !

When it comes to IP Assignments in dialups, things are a bit different than narmal LAN ip assignments.
The 32 bit subnet mask you are reffering to is something I have seen many times across dialups and is normal.

As far as the route entry and IP's assigned to the dialup clients, it would be valid depending on what you are trying to do. It is unclear why you would define a route of 192.168.0.0 255.255.255.240 <ip of your netserver> to your workstations, or I might have understood it incorrectly.

Can you provide us with more information on what exactly your trying to do ?

Cheers,

Chris P.

p.s When the ppp protocol topic is covered, be sure to find here on firewall.cx all the information you couldn't locate on the internet.

Hello Chris,

Thanks for your reply.

About routing:

Say I have the following scheme:
_
| |-(router)---(internet)---
|S| -->
|W| <--
|I|-(netserver1)
|T|
|C|-(netserver2)
|H|
|_|

router ip = 10.0.0.1
netserver1 ip = 10.0.0.2
netserver2 ip = 10.0.0.3

pool on netserver1 = 192.168.0.0/28
pool on netserver2 = 192.168.0.16/28

then I'll assign routes on router like this:

ip route 192.168.0.0 255.255.255.240 10.0.0.2
ip route 192.168.0.16 255.255.255.240 10.0.0.3

and default routes on netservers to 10.0.0.1

that all means that broadcast packet make sence only in the same subnet, and any host outside this subnet is unable to send droadcast packet to all hosts in the particular subnet correct?

Thanks [img]images/smiles/icon_smile.gif[/img]

any additional info?

Wrath Child,

All your routes seem to be correctly placed and your subnet boundries are correct.

As far as the boradcasts your talking about, the clients who connect to the netservers should not be able to send broadcasts to the networks they are attached to.

From the client's prospective (he is the one dialing to the netserver), this is what we call a stub network, and shouldn't be required to send any broadcasts to the netserver.

Now, you should also be able to configure the netserver to simply drop any broadcasts it receives from its dial in clients.

The other thing which I am thinking about right now is that if a client dials in and receives an ip address of e.g 192.168.0.10 with a subnet mask of 255.255.255.255, then my guess is that it shouldnt be able to do a "subnet broadcast" on that line, simply because of its configured subnetmask which is 255.255.255.255, though I am not 100% sure on this, its just a logical assumption on my behalf and I would be very interestead in anyone elses opinion.

Let me know what your thoughts are.

Cheers,