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The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] ipchains/firewall question
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Re: [vox-tech] ipchains/firewall question


  • Subject: Re: [vox-tech] ipchains/firewall question
  • From: Micah Cowan <mMAPSicah@cowanbox.com>
  • Date: Wed, 18 Oct 2000 13:34:06 -0700
  • References: Pine.LNX.4.21.0010181152410.2823-100000@satan
  • References: Pine.LNX.4.21.0010181310090.490-100000@mirimichi.pvusa.localnet

On Wed, Oct 18, 2000 at 01:31:16PM -0700, jdnewmil@dcn.davis.ca.us wrote:
> 192.0.0.0/255.0.0.0 falls within the 192.0.0.0-223.255.255.255 "Class C"
> address range which is supposed to use 255.255.255.0 masks, but nobody
> pays much attention to that in real routing anymore.  That is, the
> InterNIC will probably not assign you more than 256 addresses in a block
> in that range, but they may assign less and you may elect to subdivide the
> block you get further for your own routing purposes.
> 
> By blocking 192.0.0.0/255.0.0.0 you are almost certainly blocking some
> valid public ip addresses, since the class C private addresses are limited
> to 256 networks of 256 hosts each, in the range 192.168.x.y.  You probably
> want to deny 192.168.0.0/255.255.255.0.

Untrue.  The 255 in 255.0.0.0 locks all 8 bits in the first field,
which means that it *only* applies to addresses in the 192 network.
The range would be 192.0.0.0 - 192.255.255.255, not 223.255.255.255.
Still, using the given mask would still potentially block outside
traffic.  But using a filter of 192.168.0.0/255.255.255.0 would
potentially allow internal traffic from legal internal source IPs
(such as 192.168.2.45).  Use 192.168.0.0/255.255.0.0.

-MC

> 
> ---------------------------------------------------------------------------
> Jeff Newmiller                        The     .....       .....  Go Live...
> DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
> Work:<JeffN@endecon.com>              Live:   OO#.. Dead: OO#..  Playing
> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
> /Software/Embedded Controllers)               .OO#.       .OO#.  rocks...2k
> ---------------------------------------------------------------------------


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