Date: Thu, 8 Apr 2004 18:56:37 +0200 From: Paul Schenkeveld <fb-net@psconsult.nl> To: net@freebsd.org Subject: Re: do we support non contiguous netmasks ? Message-ID: <20040408165637.GA25187@psconsult.nl> In-Reply-To: <4072B048.2000509@packetfront.com> References: <20040331005914.A6934@xorpc.icir.org> <40712A8F.9000704@packetfront.com> <40716208.808CF084@freebsd.org> <4072916D.101@packetfront.com> <40729B7A.2C984BD3@freebsd.org> <4072A169.9010206@packetfront.com> <4072AA91.DA00A9F3@freebsd.org> <4072B048.2000509@packetfront.com>
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Hi,
On Tue, Apr 06, 2004 at 03:27:36PM +0200, Anders Lowinger wrote:
> I was just trying to elaborate on when/why non-contignous netmasks
> would be good to have. I'm pretty sure no-one is using them....
Actually, one of my customers uses a non-contiguous netmask for
static routes. The picture is something like this:
In a WAN they have many branch offices with a standardized IP plan
giving 8 subsequent /24 subnets (RFC1918) to each branch. At one
point in time it was decided that the second subnet of each branch
office should use an ISDN dialup network instead of the VPN because
the traffic on that subnet is only occasional but too bursty for the
VPN.
So the IP plan is:
172.18.bbbbbsss.hhhhhhhh (branches 1 - 32)
172.19.bbbbbsss.hhhhhhhh (branches 33 - 64)
where bbbbb is the branch office number (module 32) and sss the subnet
number within the branch office.
They have the following two routes on their central (FreeBSD) routers
at the main office:
route add -net 172.18.0.0 -netmask 255.254.0.0 vpn-router
route add -net 172.18.1.0 -netmask 255.254.7.0 isdn-router
Not having non-contiguous netmask would require them to install
65 static routes:
route add -net 172.18.0.0 -netmask 255.254.0.0 vpn-router
route add -net 172.18.1.0 -netmask 255.255.255.0 isdn-router
route add -net 172.18.2.0 -netmask 255.255.255.0 isdn-router
route add -net 172.18.3.0 -netmask 255.255.255.0 isdn-router
...
route add -net 172.19.255.0 -netmask 255.255.255.0 isdn-router
I agree that this use of non-contiguous netmasks is rare and I would not
object against removing them from FreeBSD if is serves the purpose of
better/faster/easier to understand/higher quality/easier to maintain
kernel code (and tell my customer that I'm sorry but we move to 65
static routes up from 2).
Greetings,
Paul Schenkeveld, Consultant
PSconsult ICT Services BV
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