Problem with multiple interfaces / multiple IPs per interface in linux, with dhcp server.

psihozefir sorin.panca at
Fri Jul 14 08:48:06 UTC 2006

Thank you for all who answered my question! I had some errors in the
past with multiple nets connected to the same computer, but I found
the "shared-network" statement and it worked... In the man page there
was no mention that if I serve multiple interfaces I have multiple
not-shared networks.
It should be: "For every interface please use a shared-network
statement, only if you have multiple addresses on that interface."

2006/7/13, Simon Hobson <dhcp1 at>:
> I assume you have a reason for this, it's very wasteful of addresses
> (you lose 3 of each block of 8) but doesn't gain you anything traffic
> wise. It's not wrong, I'm just curious.
I have an unrecommended ethernet network topology, with 8 level
cascaded without-management 8-port 100Mbit/s switches. As you can see
(if you can imagine or draw on a paper), that if i have a big /24
network and some computer on an edge wants to talk to some computer on
the other edge its MAC address would configure all the uplink ports of
all the switches that the message passes through. Now, if there are
another pair of computers sharing a part of the net with the other
two, the configured uplink MAC addresses no longer apply. So, I
devided the network into networks serving each switch, so the uplink
is always the gateway's MAC address. I know that I manged to load the
server for every transfer in the net and to reduce at half the speed
if two pairs of computers communicate simulaniously, but the fact is
that the computers more often access the internet through the gateway,
so I managed to reduce the arp traffic inside every micro-network with
this hack. My Internet link is 512 kbit/s up and max 1Mbit/s down.
I'm opened to sugestions if someone has another better ideea (not
buying managed swithes).

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