Re: netmask for loopback interfaces

> Oleksandr Kryvulia <shuriku@shurik.kiev.ua> wrote:
> 
> > 04.11.21 01:01, Mike Karels ?????:
> > > I have a pending change to stop using class A/B/C netmasks when setting
> > > an interface address without an explicit mask, and instead to use a default
> > > mask (24 bits).  A question has arisen as to what the default mask should
> > > be for loopback interfaces.  The standard 127.0.0.1 is added with an 8 bit
> > > mask currently, but additions without a mask would default to 24 bits.
> > > There is no warning for missing masks for loopback in the current code.
> > > I'm not convinced that the mask has any meaning here; only a host route
> > > to the assigned address is created.  Does anyone know of any meaning or
> > > use of the mask on a loopback address?
> > >
> > > Thanks,
> > > 		Mike
> > >
> >
> > /8 mask on loopback prevetnts using of 127.x.x.x network anywhere 
> > outside of the localhost. This described in RFC 5735 [1] and 1122 [2]
> >
> > [1] https://datatracker.ietf.org/doc/html/rfc5735
> > [2] https://datatracker.ietf.org/doc/html/rfc1122
> 
> There is a push by some people to release 127.0.0.0/8 address space,
> leaving only 127.0.0.0/16 as reserved for localhost.
> 
> https://www.spinics.net/lists/netdev/msg598545.html
> 
> https://github.com/schoen/unicast-extensions/blob/master/127.md
> 
> https://github.com/schoen/unicast-extensions/
> 
> I make no comment on the feasability of doing this!
> 
> However, that aside, aren't you just confusing the mask with routing?
> 
> I think the mask on any IP on a loopback interface should be /32
> (if you want to add a "127.0.0.0/8 -local" route even if done
> automatically", then so be it)
> 
> Note, the default FreeBSD firewall rules already have:
> 
>     ${fwcmd} add 100 pass all from any to any via lo0
>     ${fwcmd} add 200 deny all from any to 127.0.0.0/8
>     ${fwcmd} add 300 deny ip from 127.0.0.0/8 to any

Which no longer work correctly since the "to 127.0.0.0/8"
packets SHALL go out what ever interface the route table
tells them to (often the default route), AND NOT lo0.

oot {1003}# route -n get 127.1.1.1
   route to: 127.1.1.1
destination: 0.0.0.0
       mask: 0.0.0.0
    gateway: 192.168.32.8
        fib: 0
  interface: em0
      flags: <UP,GATEWAY,DONE,STATIC>
 recvpipe  sendpipe  ssthresh  rtt,msec    mtu        weight    expire
       0         0         0         0      1500         1         0

> Cheers, Jamie

-- 
Rod Grimes                                                 rgrimes@freebsd.org