Re: DHCP and secondaries

[Christopher Sulentic <[e-mail]>]

Tim,

I understand that you are probably not using a centralized DHCP server, but
here's one way to go about it...

Cisco routers have a "subinterface" feature that essentially allows each
logical IP subnet on a single physical interface to be 'primary' for it's
subinterface.  For example, on a Cisco 7000, the physical interface might
be eth 3/0.

By configuring logical subinterfaces, you can probably get DHCP Relay to
fill in the IP source/dest and giaddr fields with the primary IP address on
each of the logical subinterfaces.

In our case, we also have several logical IP subnets per physical router
segment.  We're doing the following:

        o Use a single centralized DHCP server with multiple scopes
          (a single point of failure is not so big of a deal with long leases)
        o Flatten the user LAN segments with an ethernet switch
        o Add a new (flattened) Class B IP address as the primary IP address
          on the routers ethernet (netmask is 255.255.252.0, 1000 nodes/subnet)
        o Configure DHCP on the client workstations and convert them off of
          the micro-subnetted logical segments onto the new (flattened) Class B.

>Does anyone know of a pointer to a DHCP package that
>supports the use of secondary addresses (i.e, multiple
>logical subnets on one interface)?
>
>Our campus is in the process of conversion from a classful
>routing protocol to classless, and we have a number of
>addresses on many of our Cisco router interfaces.
>Unfortunately, none of the servers that I have ported seem
>to support the use of secondaries.
>
>The servers I have checked out so far:
>
>ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.2.1.tar.gz
>ftp://sh.wide.ad.jp/WIDE/free-ware/dhcp/dhcp-1.3beta.tar.gz
>ftp://www.fugue.com/pub/dhcp/DHCPD-BETA-1.tar.gz
>ftp://ftp.net.cmu.edu/pub/dhcp/dhcp-3.3.7.tar.gz
>
>Tim Peiffer                             [e-mail]
>Networking and Telecommunications Services
>University of Minnesota                 [phone] desk
>130 Lind Hall                           [phone] problems
>207 Church St SE                        [phone] fax
>Minneapolis MN 55455-0134, USA

...........................................................................
  Chris Sulentic                        International Network Services
  Senior Network Systems Consultant     5151 Brook Hollow Parkway
  Cisco Certified Internetwork Expert   Suite 220
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