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

[Gordon Fisher <gordfisherman@gmail.com>]

On 6/3/2022 11:23 AM, Stefan Riha wrote:
> Hmm, but don't other programs do indeed interpret 10.0.0.2/24 
> differently? For example systemd-networkd interprets 10.0.0.2/24 as a 
> single Ip address in the subnet 10.0.0.0/24. Which makes a lot of 
> sense to me, because why would one specify the .2 at the end, if one 
> meant the subnet?

I would say that it depends on context; that is, what the parameter is 
supposed to be. Is it meant to specify single address, a network, or either?

In the your systemd-networkd example, IIRC, that is supposed to be a 
single IP address, and `10.0.0.2/24` is a short hand for entering 
`10.0.0.2` and `255.255.255.0` for a network interface.

Another example that comes to mind where context matters, is the older 
`route` command (that predates `ip route`), which has `-host` and `-net` 
arguments for `route add` commands, that tell the program whether to 
interpret the address part as a network based on the mask given, or as a 
single host (where the mask can be omitted.)

`ip route` on the other hand just goes by the mask given similar to `-s` 
and `-d` in `iptables`, where it really just does as it is told: check 
this address according to the given mask. And like `iptables`, assumes 
/32 if no mask is given.

-- 
gordonfish