On Mon, Sep 27, 1999 at 10:29:58PM -0400, Bob Chiodini wrote:
> Tom Reinertson wrote:
> When I initially setup Linux and pppd to my ISP, they (my ISP) told me that the
>netmask
> would be 255.255.255.252. This mask allows a subnet with two hosts, you and your
>ISP.
> I really do not understand a subnet mask of 255.255.255.255, this would imply zero
>hosts
> (invalid?). Maybe someone else could enlighten me.
The netmask is used to determine the network number from the IP address,
using a binary 'and' operation. A netmask of 255.255.255.255, when anded with
an IP address yields a network number which is the same as the IP address; a
single host network. On a point to point link like ppp this and the
default netmask of 0.0.0.0 are the only reasonable netmask values.
A netmask of 255.255.255.252 does not mean that you and the ISP share a
subnet but rather that the associated IP address belongs to a network with a
maximum of 251 hosts. This is not important, however, for a dialup client
where the default route points to the ppp link. Such a client only needs use
255.255.255.255 for the link IP network mask and 0.0.0.0 for the default
route network mask.
--
Gyepi Sam --+-- Designer/Programmer --+-- Network/System Administrator
[EMAIL PROTECTED] --+-- http://www.praxis-sw.com/gyepi
The universe is all a spin-off of the Big Bang.
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