Quickie... Hopefully!

Richard Marriner richard at syix.com
Fri Oct 1 16:58:50 PDT 2004


  This is exactly what is happening..  I have found though that if I give
the interface two Ips with ifconfig and set the default route to our newest
router (Cisco 7204) somehow I am able to do what I am wanting. (I guess the
Cisco is lots smarter than our Tiara..) I am aware that having two numbered
networks on one physical lan is not good practice, but this is only a
temporary solution and VLANs are planned for the near future.. As for our
daemons, most are running promiscuous to any IP, but I am aware I will need
to "double check" the configs..

Thank you very much for your reply..


> -----Original Message-----
> From: Kevin Glick [mailto:keving at sbfnet.com] 
> Sent: Friday, October 01, 2004 3:54 PM
> To: 'Richard Marriner'
> Cc: freebsd-questions at freebsd.org
> Subject: RE: Quickie... Hopefully!
> Richard,
> I've done the same thing a few times.  To get the full 
> description, check
> the ifconfig man page and look for "alias".  There's two 
> problems with doing
> this: first, BSD can't have two default routes.  Windows 
> allows you to set
> two default gateways, and it works because of the "Route 
> Discovery" built
> into it (this is why a windows machine can use a gateway 
> that's not on it's
> local subnet...but, that's another topic).  Second, if you've 
> got servers
> set to listen only on a specific IP (apache, etc) it still 
> won't work, even
> with the alias.
> Example:
> -->from ISP #1 \
> /->
> 					    -->hub/switch --> 
> FreeBSD fxp0 
> -->from ISP #2 /
> \->
> In the crude diagram above, both ISPs feeds end up coming 
> into a hub/switch
> that your BSD machine is plugged into.  The normal ifconfig 
> on the device is
> netmask  You would then: "ifconfig 
> fxp0 inet
> netmask alias" the device.  This will work, as 
> long as routing
> is setup correctly.  Any request for from anywhere in 
> the world
> would end up at the same machine/interface as a request for 
>  The
> problem lies in getting data out with the aliased address.  
> The default
> route on the machine would be and all traffic goes 
> there.  If you
> have specific traffic that you want to go out with the 
> address,
> you'd have to add routes for each DESTINATION IP:  "route add 
> -net
> -netmask" and so on.  BSD isn't smart 
> enough to do
> source based routing.  So the traffic will come into 
> via ISP #2, but
> the replies/ACKs will go out via ISP #1.  Any traffic 
> generated from the
> machine, without a specified SOURCE IP will go out as 
>, and get sent
> via the gateway.
> The other problem with the diagram above is that you've got 
> two subnets
> running on the same lan, which breaks most rules of 
> networking.  This can be
> remedied with a few vlans, but again, that's another topic.
> Hope this helps.  I'm sure most of this info is correct, but 
> I'm more than
> willing to have somebody set me straight.
> Kevin Glick
> ITS Manager
> keving at sbfnet.com
> Sterling Business Forms
> -----Original Message-----
> From: owner-freebsd-questions at freebsd.org
> [mailto:owner-freebsd-questions at freebsd.org] On Behalf Of 
> Richard Marriner
> Sent: Friday, October 01, 2004 3:25 PM
> To: freebsd-questions at freebsd.org
> Subject: Quickie... Hopefully!
> Dear list,
>    Just wondering if there is anyway (preferably simple.) to 
> have two ip
> addresses on the same NIC that are different networks.  
> A little background.  We are in the process of changing ISPs, 
> we now have
> two circuits going to two differnet ISPs.  Because of this 
> change we have to
> renumber our entire network.  Being an ISP ourselves we have 
> a handful of
> servers that run FreeBSD.  While trying to get one of our 
> test servers to
> talk to both networks from the internet we fail, I think 
> because even though
> your request is on the new numbers FreeBSD still trys routing 
> the response
> back through our old gateway.  Another question, I know in 
> Windows XP you
> can set two gateways, two ips, etc.  Can you do this in FBSD? 
>   Our windows
> boxes are talking fine on both networks.
> Any help or suggestions appreciated...
>        Richard Dean Marriner II
> SYIX.COM  --=--  Network Administrator
> 530-755-1751x206 - richard at syix.com
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