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

From: Jeff Vian (jvian10_at_charter.net)
Date: 06/13/04

  • Next message: Benjamin J. Weiss: "Re: DHCP for multiple subnets (was: Re: Routing and bandwidth problem)" 
    Date: Sun, 13 Jun 2004 14:35:25 -0500
To: For users of Fedora Core releases <fedora-list@redhat.com>

    Rodolfo J. Paiz wrote:

    > 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,

    Your approach works, and if you have multipl;e hosts on the same subnet
    being served it may be best, as well as providing the routing for them.

    You also should consider the technique of assigning IP address based on
    the MAC address of the requester. This technique is used to DHCP assign
    static ip addresses to servers on lots of networks. There is no need to
    be tied to one interface per subnet, but rather since the DHCP request
    broadcast includes the MAC address of the requester (as well as the
    originating network IP if routed), it can be set in the configuration
    tables to specify the address to be assigned.

    >
    > 

    -- 
fedora-list mailing list
fedora-list@redhat.com
To unsubscribe: http://www.redhat.com/mailman/listinfo/fedora-list
  • Next message: Benjamin J. Weiss: "Re: DHCP for multiple subnets (was: Re: Routing and bandwidth problem)"

    Relevant Pages

    • RE: Problems with Permissions
      ... For the "Network Configuration Wizard" not accessible issue, ... The DHCP not working properly issue may due to DNS not correctly ... ipconfig /all on SBS server, ...
      (microsoft.public.windows.server.sbs)
    • Re: networking private and public hosts questions
      ... some systmes in storage to create a test network. ... a WS to the child and attempted to pull an IP from the DHCP server, ...
      (microsoft.public.win2000.networking)
    • Re: Multiple IP Schemes for Different Buildings
      ... The linksys on your first network stays as it is, ... DHCP broadcast is on the local subnet only, ... router to forward internet traffic to your firewall. ... If each server has it's own DHCP server then I don't need to worry ...
      (microsoft.public.windows.server.general)
    • Re: Any Way to Pass DHCP From Internal to Perimiter?
      ... WON'T BE a separate network. ... Regardless of the above DHCP operations are confined to the "physical" ... subnet where the DHCP server resides. ... DHCP relay service on your ISA server itself, then of course you will have ...
      (microsoft.public.isa)
    • Re: Slow Network Speed from 2008 Server
      ... Network Adaptor properties which are a bit scary. ... I'm running AD on it as well as SQL Server 2005. ... that the DHCP didn't work. ...
      (microsoft.public.windows.server.networking)