Network mask 255.255.255.255

Network mask 255.255.255.255

Post by Mishk » Thu, 24 Jul 2003 02:39:27



Greetings!

Anybody knows what is a meaning of netmask 0xffffffff?
Is it have an any sense?

Lets assume we have configured some (and single) network interface:
IP - 192.168.1.1, netmask - 255.255.255.255.

So my questions are:
1) can I access any host via network interface configured in such manner?
2) can I create (and how) the route entry to, for examle, 172.16.1.0 LAN?
3) it is possible create any route entry VIA 172.16.0.1 host?
4) are all above will works in real life?

Any ideas would be appreciated.

--
TIA, Mishka.

P.S. Excuse me for possible offtopic and crossposts.

 
 
 

Network mask 255.255.255.255

Post by Rob MacGrego » Thu, 24 Jul 2003 03:01:05



> Greetings!

Hmmm, crossposted to half the universe.  Sure you couldn't have found a
few more groups?

Quote:> Anybody knows what is a meaning of netmask 0xffffffff?
> Is it have an any sense?

Nope, it says that every bit is the network address and there is no host
address.  The longest usable netmask is a /30, giving 2 IPs (plus the
network address and broadcast address).

Quote:> Lets assume we have configured some (and single) network interface:
> IP - 192.168.1.1, netmask - 255.255.255.255.

Then lets assume you don't have a network :-)

Quote:> So my questions are:
> 1) can I access any host via network interface configured in such manner?

I'd hope not, or you've got a broken OS (IMHO).

Quote:> 2) can I create (and how) the route entry to, for examle, 172.16.1.0 LAN?

Nope.

Quote:> 3) it is possible create any route entry VIA 172.16.0.1 host?

Nope.

Quote:> 4) are all above will works in real life?

Nope.

--
   Rob MacGregor (BOFH)        Oh my God! They killed init! You bastards!
       The light at the end of the tunnel is an oncoming dragon.

 
 
 

Network mask 255.255.255.255

Post by Barry Margoli » Thu, 24 Jul 2003 03:47:14




>Anybody knows what is a meaning of netmask 0xffffffff?
>Is it have an any sense?

It's the mask for a host-specific route, rather than a subnet.

Quote:>Lets assume we have configured some (and single) network interface:
>IP - 192.168.1.1, netmask - 255.255.255.255.

This is typically only meaningful on loopback or point-to-point
interfaces.  It can also be OK for alias addresses.

Quote:>So my questions are:
>1) can I access any host via network interface configured in such manner?

You can have routes that point to the interface.  If it's a point-to-point
interface (e.g. a tunnel, a serial line) the packets will simply be sent to
the device at the other end.

--

Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

 
 
 

Network mask 255.255.255.255

Post by Andreas Wies » Fri, 25 Jul 2003 00:19:00




>> Greetings!

> Hmmm, crossposted to half the universe.  Sure you couldn't have found a
> few more groups?

>> Anybody knows what is a meaning of netmask 0xffffffff?
>> Is it have an any sense?

> Nope, it says that every bit is the network address and there is no host
> address.  The longest usable netmask is a /30, giving 2 IPs (plus the
> network address and broadcast address).

... for the case you don't run Windoze. There you can also select a
network mask of /31 without getting an error message...

[snip...]

Regards,

awiese
--
Ich koennte mir durchaus vorstellen, dass ein IE oder aehnlicher Browser
einer SuSE-Distribution in Zukunft beiliegen koennte. Wuerde mein Bild
von dieser Distribution vervollstaendigen.
  -- Kim Huebel in de.comp.os.unix.linux.misc

 
 
 

Network mask 255.255.255.255

Post by Mish » Fri, 25 Jul 2003 00:53:46





> >Anybody knows what is a meaning of netmask 0xffffffff?
> >Is it have an any sense?

> It's the mask for a host-specific route, rather than a subnet.

Yup. And seems to be impossible use it as source address, isn't it?
However...

Quote:

> >Lets assume we have configured some (and single) network interface:
> >IP - 192.168.1.1, netmask - 255.255.255.255.

> This is typically only meaningful on loopback or point-to-point
> interfaces.  It can also be OK for alias addresses.

How about single Ethernet interface, configured in that way as primary
single IP? This is possible on Windows boxes! But on my NetBSD i can't
use it.

Quote:

> >So my questions are:
> >1) can I access any host via network interface configured in such manner?

> You can have routes that point to the interface.  If it's a point-to-point
> interface (e.g. a tunnel, a serial line) the packets will simply be sent to
> the device at the other end.

Yes, in this case netmask value just ignored. Only two hosts may be
linked in P2P networks and it must be always two.

Maybe Windows machines define this config as virtual point-to-point?

Thanks a lot for you very helpful answer!

--
Best regards,
Mishka.

 
 
 

Network mask 255.255.255.255

Post by Mish » Fri, 25 Jul 2003 01:02:30




> > Greetings!

> Hmmm, crossposted to half the universe.  Sure you couldn't have found a
> few more groups?

> > Anybody knows what is a meaning of netmask 0xffffffff?
> > Is it have an any sense?

> Nope, it says that every bit is the network address and there is no host
> address.  The longest usable netmask is a /30, giving 2 IPs (plus the
> network address and broadcast address).

For point-to-point it is possible, but for other - ? Maybe you are
right.

Quote:

> > Lets assume we have configured some (and single) network interface:
> > IP - 192.168.1.1, netmask - 255.255.255.255.

> Then lets assume you don't have a network :-)

No. It's usual Ethernet.

Quote:

> > So my questions are:
> > 1) can I access any host via network interface configured in such manner?

> I'd hope not, or you've got a broken OS (IMHO).

Yes, if it is Windows. The answers to my other questions (at least 3
and 4) will be "yes" in case if Windows use. But my other question: Is
it correct? My ISP offers me such config via him DHCP service. Thus,
my NetBSD box is convinced :(

Anyway, thank you for you things.

--
BR, Mishka.

 
 
 

Network mask 255.255.255.255

Post by Barry Margoli » Fri, 25 Jul 2003 03:16:35








>> >Anybody knows what is a meaning of netmask 0xffffffff?
>> >Is it have an any sense?

>> It's the mask for a host-specific route, rather than a subnet.

>Yup. And seems to be impossible use it as source address, isn't it?
>However...

If the recipient has a route back to it, it should work OK.  For instance,
if it's the address of your serial port, the ISP should be able to route it
down your serial line.

Quote:>> >Lets assume we have configured some (and single) network interface:
>> >IP - 192.168.1.1, netmask - 255.255.255.255.

>> This is typically only meaningful on loopback or point-to-point
>> interfaces.  It can also be OK for alias addresses.

>How about single Ethernet interface, configured in that way as primary
>single IP? This is possible on Windows boxes! But on my NetBSD i can't
>use it.

Windows is pretty simplistic about its routing.  It associates the default
route with an adaptor, so it sends traffic to the default gateway through
that adaptor regardless of whether the gateway is in the same subnet as the
interface's address.  Most other operating systems determine which
interface to use by looking for the one whose subnet includes the gateway
address, so a network mask that doesn't identify the correct subnet is
pretty useless.

--

Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

 
 
 

Network mask 255.255.255.255

Post by Mishk » Fri, 25 Jul 2003 04:16:23





>>How about single Ethernet interface, configured in that way as primary
>>single IP? This is possible on Windows boxes! But on my NetBSD i can't
>>use it.

> Windows is pretty simplistic about its routing.  It associates the default
> route with an adaptor, so it sends traffic to the default gateway through
> that adaptor regardless of whether the gateway is in the same subnet as the
> interface's address.  Most other operating systems determine which
> interface to use by looking for the one whose subnet includes the gateway
> address, so a network mask that doesn't identify the correct subnet is
> pretty useless.

If this so, it is very interesting what Windows will do when it
will have two (or even more) interfaces configured as, for example,
192.168.1.1/255.255.255.255 and 192.168.2.1/255.255.255.255, and
attached into two independent LANs, and now we need add a route to
host 172.16.1.1? What's interface will be used in such case?
First choosen?

--
Mishka.