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DHCP on subinterface in FreeBSD

Posted on 2004-03-30
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Last Modified: 2013-12-23
Ok, this might be a yes or no question.  I am running FreeBSD 5.2-Release on a home box as a Cable Router/NAT Gateway.  My question is whether or not I can use DHCP on a sub-interface (alias interface).

I added this
ifconfig_de0="DHCP"
ifconfig_de0_alias0="DHCP"

to my rc.conf but when I do a "ifconfig" I don't see it at all, just the actuall interface and no aliases.
#ifconfig
de0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        inet6 fe80::2c0:f0ff:fe37:8720%de0 prefixlen 64 scopeid 0x1
        inet 67.*.*.* netmask 0xffffff80 broadcast 255.255.255.255
        ether 00:c0:f0:37:87:20
        media: Ethernet autoselect (10baseT/UTP)
        status: active
xl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=b<RXCSUM,TXCSUM,VLAN_MTU>
        inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255
        inet6 fe80::250:daff:fe1c:311d%xl0 prefixlen 64 scopeid 0x2
        inet 192.168.1.100 netmask 0xffffffff broadcast 192.168.1.255
        ether 00:50:da:1c:31:1d
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
plip0: flags=8810<POINTOPOINT,SIMPLEX,MULTICAST> mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet 127.0.0.1 netmask 0xff000000
        inet6 ::1 prefixlen 128
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x4

I am running NATD on the internal interface (xl0) and de0 is the external interface.
What I am wanting to do is

real_ip1 -----
                   \                                                                ---- LAPTOP
                    \                                                             /
                     -----   BSDBOX                                       /
                     -----   acting as router  ----- SWITCH -----
                    /                                                            \
                   /                                                              \
real_ip2 -----                                                                 ---- DESKTOP

Ok... This is what I want it to look like.  But I would like for "real_ip1" to go to BSDBOX, which it does now...  "real_ip2" I would like on a subinterface on the same NIC as "real_ip1".   If somebody were to come in via "real_ip1" it would go to the BSDBOX, "real_ip1" would also be used for NAT for the Laptop.  If somebody were to come in via real_ip2 I would like the BSDBOX to basically forward everything from that IP directly to DESKTOP (basically DMZ).

Is all this fiasco possible?  At this point my road block is getting the DHCP on the subinterface.  But if the rest of the setup isn't possible I am not going to continue to try to get it working.

Thank You
Richard Marriner
richard at syix dot com
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Question by:rmarriner
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4 Comments
 
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Expert Comment

by:Alf666
ID: 10717720
DHCP is a "cable based" protocol. It sends a request on a broadcast UDP addr and listens for packets coming back on the medium.

The IP addr is given to you by refering your ethernet addr.

As your alias interface is on the same medium as your main interface, it will never get a second address from a DHCP server.
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Author Comment

by:rmarriner
ID: 10717768
So if I were to add another NIC (which would make three...) in theory this would work?
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Accepted Solution

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Alf666 earned 500 total points
ID: 10718006
Not only in theory. Practically also, yes. But I don't really see the advantage.
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Author Comment

by:rmarriner
ID: 10718352
Thanks.
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