Re: FreeBSD and IP aliases .

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On Sun, Jan 26, 2003 at 11:16:57PM +0100, Dirk-Willem van Gulik wrote:
dirkx>  Interface wi5 matches multiple shared networks
dirkx> 
dirkx> Which is a bit counter intuitive; as you MUST add those for any other
dirkx> interfaces you do not run DHCP on.

You can't just run DHCP on only one of the IP interfaces in this
scenario, since DHCP runs on the physical interface, not the
logical IP sub-interfaces.  Some DHCP requests come in as all-ones
broadcast 255.255.255.255, so how would the OS know which IP
sub-interface to send that traffic to? Likewise with outgoing
broadcasts.  They all end up on the same wire, and there is no way
to distinguish between them.  That is the price you pay for using
shared-networks (instead of e.g. VLANs and 802.1Q).

The correct solution (besides not using IP aliasing) is to put all
such shared-networks inside a shared-network statement:

shared-network FOO {
        subnet { ... }
        subnet { ... }
}

You can then deny booting or whatever on the subnets you do not
wish to serve.  You can also set the IP address the server binds
to for unicast packets:

local-address a.b.c.d;

which was recently discussed:

http://marc.theaimsgroup.com/?l=dhcp-server&m=104221495822917&w=2

(In that case, there was no IP aliasing, and the IP interfaces
were on separate physical interfaces.)

-- 
Charles R. Anderson <cra@xxxxxxx> / http://angus.ind.wpi.edu/~cra/
PGP Key ID: 49BB5886
Fingerprint: EBA3 A106 7C93 FA07 8E15  3AC2 C367 A0F9 49BB 5886


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