Re: DHCP for multiple subnets (was: Re: Routing and bandwidth problem)

From: Rodolfo J. Paiz (rpaiz_at_simpaticus.com)
Date: 06/13/04

  • Next message: Rodolfo J. Paiz: "Re: DHCP for multiple subnets (was: Re: Routing and bandwidth problem)" 
    Date: Sun, 13 Jun 2004 13:08:32 -0600
To: For users of Fedora Core releases <fedora-list@redhat.com>

    At 06:25 6/13/2004, Matt . wrote:
    >The DHCP server shouldn't care what interface the request came in on,
    >rather it looks at the source network of the request.

    I'm no expert on DHCP, but I continued this thread since no one around here
    was able to help me solve this problem earlier. Hence, having found a
    solution I'm posting it.

    Having said the "not an expert" bit, how the heck is a computer who does
    not know what network it's on going to provide a source network for the
    DHCP server? It wakes up, yells out a broadcast request for a DHCP server,
    and the server has to answer that. The *only* way I see to do that is via
    the network interface on which the request arrived at the router.

    >So you server could support many different ranges, provided there was
    >suitable separation (i.e. a router) between the subnets and the server.

    But that's precisely the point! We were seeking a way for *one* machine to
    act as a router/firewall/gateway/dhcpd for four subnets that are directly
    connected to it. No other routers exist in this scenario. Of *course* if
    another router existed, it'd be a piece of cake. But the question was: if
    this is the only router providing Internet access for four separate
    networks who are currently not connected to anything and don't have
    routers, how do you manage to assign them separate subnets via DHCP?

    Only two solutions appear to exist and be functional: buying $75 Netgear
    blue boxes to do DHCP for the subnets and masquerading so that all traffic
    to my server comes from a single IP address, and setting up separate
    interfaces on my router box. The "blue box" route was discarded due to the
    expense (why spend $300 if not necessary), the additional points of failure
    (despite being highly reliable), the additional configuration and
    maintenance required, and the slightly lower functionality (if one user on
    those subnets were abusing bandwidth, it'd be hell to find them).

    Having chosen to do it all on one box, the challenge appeared to be for
    DHCPd to issue different addresses based on the interface on which the
    request arrived. The documentation appeared to offer no easy way to do
    this, and I interpreted that to mean that it would be a difficult
    challenge. Turns out, it's automatic!

             1. You *should* configure your dhcpd.conf for every subnet on
    which your server has an interface even if the DHCP server does not assign
    addresses (i.e. the subnet block does not include a range statement).

             2. The server will then automatically assign an address in the
    correct subnet for every incoming request, assuming that it's been told to
    assign addresses on that subnet via a range statement. Nothing more to be done.

    Too simple. <grin>

    Cheers, 

    -- 
Rodolfo J. Paiz
rpaiz@simpaticus.com
http://www.simpaticus.com
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  • Next message: Rodolfo J. Paiz: "Re: DHCP for multiple subnets (was: Re: Routing and bandwidth problem)"

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