Reverse IP NAT to secondary IP address

From: Nils Vogels (nivo+sender+8eb026_at_yuckfou.org)
Date: 10/25/03

  • Next message: _at_babolo.ru: "Re: Reverse IP NAT to secondary IP address" 
    Date: Sat, 25 Oct 2003 21:04:23 +0200
To: freebsd-net@freebsd.org

    Hi there!

    I'm trying to solve a situation that I have with a device which needs
    SNMP polling, but is not normally reachable to the outside world,
    because it cannot install a default gateway.

    In short, a situation scetch:

                                                                             
                SNMP-server (192.168.2.2/24)
                                                                                             
    -----------
    +------------+ +-------------+
                 |
    | WWW |--------------------| Gateway | --------------+
    +------------+
    +-------------+ |
        192.168.0.2/24 192.168.0.1 IP: 195.x.x.x.x
    \-----> Internet (0.0.0.0/0)
                                             (rl0) Alias:
    192.168.2.1
                                                                             
    (ed0)

    Now what I am trying to do is get statistics from the SNMP-server into
    the WWW box, but I am stuck on the following:

    WWW is a FreeBSD-4.8 box.
    Gateway is a FreeBSD-4.8 box with IP Filter
    Since the SNMP-server does not have a default route, the traffic needs
    to originate from an IP address within the same subnet as the Gateway.
    To that end, I have added an alias IP of 192.168.2.1 to the gateway.
    When I run an snmpwalk from the gateway all goes fine.

    Since the traffic is coming from WWW and heading through the Gateway,
    which does not bridge, I have to perform some form of NATting in the
    gateway.

    I've been searching and attempting various redirects and map entries,
    and am now stuck at:

    map rl0 from 192.168.0.0/24 to 192.168.2.0/24 port = 161 -> 192.168.2.1/32

    I think I'm close .. can someone give me the final hint ? ;-)

    Thanks,

    Nils.
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  • Next message: _at_babolo.ru: "Re: Reverse IP NAT to secondary IP address"

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