Re: single host netmask (255.255.255.255)

David D wrote:
I know. but Netengs post you referred to was also talking about broadcast address. 

Please, read Neteng`s post carefully, we are talking about HOST ROUTING.


I can't imagine why you would want to assign a 255.255.255.255 mask to an ethernet interface as you then can't talk to someone (se my drevious post)


It is simple: Imagine, you have router with three interfaces, you are use dynamic routing OSPF protocol. The routes from three interfaces, propagate via OSPF to the rest of network.... You wanna to manage this router remotely, in case the some interface(s) are down.... One way is to remember IP addresses assigned to each interfaces, but more smart solution is to assign to this machine one EXTERNAL LOOPBACK address (single IP with mask 255.255.255.255, in other words SINGLE HOST assigned to Microsoft loopback adapter), and propagate this address (in other words: SINGLE HOST NETWORK) to OSPF. Than you can access this machine by this one IP address, does not care which interfaces are up or down. In the UNIX word, usual thing......

P.L.

BTW: sorry for my horrible english, but I think yo can understand what I mean....


/D

Petr Laznovsky wrote:

David,

we are talking about __MASK__ 255.255.255.255, not the broadcast address!!!

P.L.

David D wrote:

 From RFC919

<snip>
  The address 255.255.255.255 denotes a broadcast on a local hardware
  network, which must not be forwarded.  This address may be used, for
  example, by hosts that do not know their network number and are
  asking some server for it.

  Thus, a host on net 36, for example, may:

     - broadcast to all of its immediate neighbors by using
       255.255.255.255

     - broadcast to all of net 36 by using 36.255.255.255

  (Note that unless the network has been broken up into subnets, these
  two methods have identical effects.)

  If the use of "all ones" in a field of an IP address means
  "broadcast", using "all zeros" could be viewed as meaning
  "unspecified".  There is probably no reason for such addresses to
  appear anywhere but as the source address of an ICMP Information
  Request datagram.  However, as a notational convention, we refer to
  networks (as opposed to hosts) by using addresses with zero fields.
  For example, 36.0.0.0 means "network number 36" while 36.255.255.255
  means "all hosts on network number 36".
</snip>


Petr Laznovsky wrote:




Is single host netmask allowed on ethernet interface in Windows 2000? I need to assign IP 10.1.1.1 with netmask 255.255.255.255 to ETH interface, but i`v got following error message: "Invalid IP or subnet mask address". As I remember, dial-up DHCP requested address come normally with this mask..... Wha is wrong??????

L. 






I think you remember wrong, fresch up your you basic tcp/ip knowledge.

The smallest usable net consists of 4 adresses (netmask 255.255.255.252)

First adress (host part all zero) is the net address.
Then come two addresses for hosts, you use on for your host and one for the default gateway (you want to talk to someone aren't you ?)
Last address is the broadcast address.

/David 





David, please read Neteng`s answer to my question.

P.L. 
.

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