Re: adsl route

[Debian EN <deben@fuckaround.org>]

sorry for the mistake :-/

network /30 on both

Pol

On 11/03/2017 11:57 AM, Pascal Hambourg wrote:
> Le 03/11/2017 à 10:32, Debian EN a écrit :
> > Hello to all :-) I've fastweb italian adsl
> >
> > 2 networks interfaces:
> >
> > wan 192.168.0.2/31 --> modem 192.168.0.1/31
> > eth0 192.168.1.0/24
> >
> > everything works but:
>
> Really ? It shouldn't.
> 192.168.0.1/31 and 192.168.0.2/31 are not in the same subnet.
>
> $ ipcalc 192.168.0.1/31
> Address:   192.168.0.1          11000000.10101000.00000000.0000000 1
> Netmask:   255.255.255.254 = 31 11111111.11111111.11111111.1111111 0
> Wildcard:  0.0.0.1              00000000.00000000.00000000.0000000 1
> =>
> Network:   192.168.0.0/31       11000000.10101000.00000000.0000000 0
> HostMin:   192.168.0.0          11000000.10101000.00000000.0000000 0
> HostMax:   192.168.0.1          11000000.10101000.00000000.0000000 1
> Hosts/Net: 2                Class C, Private Internet, PtP Link RFC 3021
>
> $ ipcalc 192.168.0.2/31
> Address:   192.168.0.2          11000000.10101000.00000000.0000001 0
> Netmask:   255.255.255.254 = 31 11111111.11111111.11111111.1111111 0
> Wildcard:  0.0.0.1              00000000.00000000.00000000.0000000 1
> =>
> Network:   192.168.0.2/31       11000000.10101000.00000000.0000001 0
> HostMin:   192.168.0.2          11000000.10101000.00000000.0000001 0
> HostMax:   192.168.0.3          11000000.10101000.00000000.0000001 1
> Hosts/Net: 2                Class C, Private Internet, PtP Link RFC 3021
>
> If the prefix length on the modem is really /31, then the only other 
> address in the same subnet is 192.168.0.0, not 192.168.0.2.
>
> At first glance it may look odd because this address is usually reserved 
> as the network address, but /31 is an exception per RFC 3021 : the two 
> addresses are usable as host addresses on a point-to-point link, there 
> are neither reserved network nor directed broadcast addresses. Otherwise 
> a /31 subnet would be useless, as it would contain only the reserved 
> network and broadcast addresses, leaving no room for host addresses.
>
> But are you sure the prefix length on the modem is /31 and not /30 ?
> With /30, 192.168.0.1 and 192.168.0.2 would be the two host addresses in 
> the subnet.
>
> $ ipcalc 192.168.0.1/30
> Address:   192.168.0.1          11000000.10101000.00000000.000000 01
> Netmask:   255.255.255.252 = 30 11111111.11111111.11111111.111111 00
> Wildcard:  0.0.0.3              00000000.00000000.00000000.000000 11
> =>
> Network:   192.168.0.0/30       11000000.10101000.00000000.000000 00
> HostMin:   192.168.0.1          11000000.10101000.00000000.000000 01
> HostMax:   192.168.0.2          11000000.10101000.00000000.000000 10
> Broadcast: 192.168.0.3          11000000.10101000.00000000.000000 11
> Hosts/Net: 2                     Class C, Private Internet

--
Pol