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Date:      Thu, 4 Nov 2021 07:28:02 -0700 (PDT)
From:      "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net>
To:        Oleksandr Kryvulia <shuriku@shurik.kiev.ua>
Cc:        freebsd-net@FreeBSD.org
Subject:   Re: netmask for loopback interfaces
Message-ID:  <202111041428.1A4ES2VL029643@gndrsh.dnsmgr.net>
In-Reply-To: <3244c917-d08a-c72b-5b5a-f74233cf47f5@shurik.kiev.ua>

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> 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

Saddly that no longer works correctly since there is no longer
a 127/8 route in the table.  Which, IMHO, is a mistake.

-- 
Rod Grimes                                                 rgrimes@freebsd.org



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