Re: question about net address

[David Christensen <dpchrist@holgerdanske.com>]

On 3/19/23 03:28, coreyh@free.fr wrote:
> On 19/03/2023 18:00, David Christensen wrote:
> > On 3/18/23 16:31, coreyh@free.fr wrote:
> > > On 19/03/2023 06:17, Kushal Kumaran wrote:
> > > > On Sat, Mar 18 2023 at 07:28:23 PM, coreyh@free.fr wrote:
> > > > > Hello
> > > > >
> > > > > I know 192.168.1.0/24 is a valid C range for network address.
> > > > >
> > > > > but what does 192.168.1.1/24 mean?
> > > > >
> > > > > I ask this just for a setting in the SPF:
> > > > >
> > > > > spf.pinoad.se.        300    IN    TXT    "v=spf1 
> > > > > ip4:188.66.63.1/24 -all"
> > > >
> > > > It means the same thing.  192.168.1.1/24 is the same range as
> > > > 192.168.1.0/24, but written by someone not paying too much attention.
> > >
> > >
> > > That's correct. Thanks.
> >
> >
> > AIUI:
> >
> > * 192.168.1.0/24 identifies an IPv4 network with an address of
> > 192.168.1.0 and a network prefix of 24 bits.  The address is within
> > the reserved private block 192.168.0.0/16.  The prefix corresponds to
> > a class C network.
> >
> > * 192.168.1.1/24 identifies an IPv4 network interface with an address
> > of 192.168.1.1 and a network prefix of 24.  The interface is
> > configured to communicate over the 192.168.1.0/24 network.
>
> So for Inleed (a local ISP)'s SPF:
>
> spf.pinoad.se.        300    IN    TXT    "v=spf1 ip4:188.66.63.1/24 -all"
>
>
> They specify only 188.66.63.1 to send email?
>
> But as far as I know their mailserver is 188.66.63.2:
>
> mail.inleed.xyz.    300    IN    A    188.66.63.2
>
>
> Then this mail server should have problems in messages delivery.
>
> Thanks
> Corey

If I correctly understand Sender Policy Framework SPF Record Syntax:

http://www.open-spf.org/SPF_Record_Syntax/


The phrase "ip4:188.66.63.1/24" in the above DNS SPF record states that 
outgoing mail will come from hosts in the address block 188.66.63.1/24.


The address 188.66.63.2 is within the published address block, so the 
ISP is stating that mail sent by that host is legitimate.


On 3/19/23 03:38, coreyh@free.fr wrote:
> So,
>
> * 188.66.63.1/24 is a range, not a single host in SPF
> * why it's not written as 188.66.63.0/24 which is more clear?
>
> Thanks


I agree that "188.66.63.0/24" would be a more conventional way to 
specify a network address block.  Perhaps you should ask the ISP why 
they used "188.66.63.1/24".


David