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SubjectRE: howto disable auto route setup?

> -----Original Message-----
> From:
> []On Behalf Of Richard B.
> Johnson
> Sent: Tuesday, February 02, 1999 10:50 AM
> To: Neil Conway
> Cc: Mike Jagdis; Sam Mortimer;
> Subject: Re: howto disable auto route setup?
> [SNIPPED (most all)]
> >
> > Vaguely on this topic, I've been wondering if it's
> legal/advisable/safe
> > to have a netmask like ?
> >
> Yes. My netmask is
> My network runs from ->
> is the "network" address, is the
> "broadcast" address. Because of some defective software in some
> machines, we don't use, 41.255, 42.255, 43.255,
> 44.255, 45.255, or 46.255 because some machines think that these
> are broadcast addresses. The machines that abuse these addresses are
> M$garbage machines.

Show me the RFC where it says this is legal all of a sudden.

> The idea of class A->C networks has come and gone because of the
> lack of suitable continuous addresses defined by the original
> standard. It is now common to make large networks using contiguous
> small networks. The netmask is the thing that defines the "network".
> Stuff that doesn't fit through the mask is sent/received through
> the "default" route. Once this is understood, configuring a network
> is simple.

I don't remember the RFC that says this either. Try to configure a Bay
router with a subnet mask less than the class of network for the IP. Can't
do it. I'd try on a cisco router, but I don't have one available at the
moment. I doubt it would let you setup an >interface< with an illegal
netmask either. If it does, then it's a bug.

> > Anyone? The HOWTO is rather ambiguous about it. I think
> it's legal,
> > but am not entirely sure. This also seems to imply a
> broadcast addr. of
> > something like for a network address of,
> > presumably that's OK too?
> The broadcast address is the IP number that will be put into packets
> that have a hardware destination of ff:ff:ff:ff:ff:ff (did I put in
> enough). These packets are received by everyone on the LAN. They
> will be received regardless of the IP number contained therein. For
> compatibility, its a good idea that the address be within the LAN
> range, and contain .255 as its last number. However, some OS don't
> care because they never check. Stuff that goes out in the Internet
> is changed and cleaned up by the router. Ethernet hardware addresses
> are not used on a WAN (like the Internet).

Just because we can make it work with Linux does not mean it is the right
thing to do. If we ever want Linux to be accepted for mission critical
tasks in the big glass house then it must interoperate with all other
devices that follow standards. We can't make up our own as we see fit.
Does Windows support this? What about HP-UX? Solaris? AIX? Digital
(Tru64) Unix? DG-UX? Irix? VMS? Novell Netware? Cisco routers? Bay
(Nortel) routers? 3Com routers? OS/2? BeOs? *BSD?

If it is not specifically specified in an RFC or other standards document
that it is now acceptable to "reverse subnet" IP addresses then the answer
to all of the questions above must be yes for this to be right. If there is
lack of an official standard, then there must be an "Industry" standard for
it to be standard. I don't think even a majority of the vendors listed
above support this, let alone a super majority that would constitute an
Industry standard.

Some questions.

What is your default router? Wouldn't happen to be something like is it? Do you multinet on your router, where you specify the
"correct" subnet mask of at least May be so that those
stupid Windows boxen can talk to each other? If so, have you actually
looked at the traffic on your network? You might be sending everything
through the router and duplicating traffic on your network. At least the
Windows boxen would send any replies through the router if you were not in
the same Class C network. may be the subnet mask for your
"network" as viewed from the Internet, which supports CIDR and aggregation
of routes, but don't confuse routing protocols with IP interfaces. Failure
to properly configure a network on your part does not constitute acceptance
of a supposed industry standard on my part.

It's just like the zero subnet thing. Yes, most router vendors support it.
But, a lot of clients don't so it is generally discouraged unless you are at
the end of your rope and there are absolutely no alternatives. That's why
it is disabled by default on most router vendors who do support it - it's a
bad idea.


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