Aliased ip's and DHCP

[Shane Kerr]

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Simon Hobson wrote:
> Javier Ubillos wrote:
> 
>> The ips are form a /23 (or possibly a /22) subnet.
> 
> Hmm, 5 is an odd number then !
> 
> 
>> I have considered the "get more nics" solution, however, it would be
>> nice to solve it using only one cable.
> 
> The other thought was virtual nics and a bridge (as used in Xen) - I
> don't know how hard it would be to set up an arrangement like this
> without the overkill of also running at least one virtual machine to
> host them.

An easier way would be to manually simulate a single DHCP client that requests
multiple leases. So, something like:

- - Fire up a DHCP client with a client identifier.
- - Get lease.
- - Save lease information.
- - Kill DHCP client *without* returning lease.
- - Repeat 5 times with different client identifiers.
- - Set the IP addresses on the same interface.
- - Before leases expire, run the clients one at a time to renew the leases.


If the DHCP server doesn't recognize the client identifiers, you might have to
change the MAC address on the card ("ifconfig eth0 hw ether 00:11:22:33:44:55"
in Linux).


It's a bit brittle, but it just might work.


I considered a DHCP option to allow the client to tell the server to send
responses to a different port, which would allow multiple clients to run on a
single interface. Mostly useful for testing, but also useful in this case. Of
course, it entails some security problems, but not too bad since DHCP packets
from the server go back to the MAC address that generated the packet, and DHCP
tends to run on closed networks.

- --
Shane
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