Re: Possibly dangerous interpretation of address/prefix pair in -s option

[Gordon Fisher <gordfisherman@gmail.com>]

On 6/8/2022 7:34 AM, Stefan Riha wrote:
>> The mask is unconditionally applied to the IP address.
> Yes. Note again that it is unconditionally applied by other programs too, yet they do not discard the full ip address. When I use 10.0.0.2/24 in the "Address=" keywork of a systemd-networkd configuration, then the the mask is used to compute a prefix route (which is automatically added if not otherwise declared). Yet the full Ip address is kept, and assigned to the nic.

This is a different context and meaning than the usage in `iptables`.

In `systemd-networkd`, that is a host address field, not a network 
address field, and that specifying a length, a la 10.0.0.2/24, is short 
hand for configuring IP address 10.0.0.2 with a mask 255.255.255.0 as 
this is for configuring an address on a network interface, which 
normally requires an IP address and a mask pair.

Where as in `iptables`, an address supplied to -d or -s is is a network 
address field that defaults to /32 when no length is specified, which is 
a single address.

It makes all the difference if the field if is a network field or an 
single address field.

-- 
gordonfish