Re: do we support non contiguous netmasks ?

From: Paul Schenkeveld (fb-net_at_psconsult.nl)
Date: 04/08/04

  • Next message: Marc G. Fournier: "RE: Stupid question about managed switches" 
    Date: Thu, 8 Apr 2004 18:56:37 +0200
To: net@freebsd.org

    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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