Two IPs on one NIC
Simon Hobson
dhcp1 at thehobsons.co.uk
Wed Sep 16 18:43:25 UTC 2009
Jeff Haran wrote:
>Just an FYI, I was able to run two dhcpcd client instances on the
>same linux machine (custom Brocade hardware platform) to accomplish
>this. Each client instance had to be passed a unique client ID on
>it's command line and likewise one was started up to service an
>interface name while the other was started up to service an
>interface alias, e.g. eth0 and eth0:0. The only other things that I
>can recall were to make sure each client instance locate it's data
>files in a separate directory, but that was just a command line
>option in the script that started them, and to modify the way the
>client generated it's XID so that each XID was unique. The
>unmodified dhcpcd client code generated it's XID using a hash of the
>MAC address and time(), which meant that each client generated the
>same XID which confused the servers big time. I just added the pid
>of the client process to what got hashed to make sure each client
>got it's own XID.
Right, so you generated client-ids that would ensure churn by
changing one every boot - thus appearing to be a different client to
the server.
And you did nothing to deal with the ambiguities of routing ? One
client gets router A, the other gets router B - what is your default
route now ? You lose one of the leases for some reason, now what is
your default route and how does it get set properly ?
Similarly DNS servers - if you lose one lease, that could potentially
mean you lose access to the DNS servers configured.
As I suggested, there are a lot of combinations of sequences to
consider, and a lot of potential conflicts. Far from trivial - though
many of them also apply if you use DHCP client on two separate
interfaces.
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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