prevent ip conflict in dhcp client
genie at geniechka.ru
Thu Jul 11 11:45:50 UTC 2013
The idea that for the internal networks you should use so-called private
address space (unless you are a big organization that need and can get a
public address block of its own). You can read about it in more detail here
So, for your upstream interface you use the address obtained via DHCP from
For your internal networks you use private blocks, for example:
Network 1: 192.168.0.1 mask 255.255.255.0
Network 2: 192.168.1.1 mask 255.255.255.0
Network 3: 192.168.2.1 mask 255.255.255.0
And you configure NAT on the router to perform address translation for the
external connections (See FreeBSD handbook for that).
Personally I think ipfilter/ipnat
(http://www.freebsd.org/doc/handbook/firewalls-ipf.html) is more easy and
convenient but other people probably will have other opinions =)
If you don't have a public IP address (sometimes this is optional service
that costs extra money) and it happens that your provider also uses
192.168.x.x block in ITS internal network (that is EXTERNAL for you), just
change your internal networks to some other block.
From: s m
Sent: Thursday, July 11, 2013 3:18 PM
Subject: Re: prevent ip conflict in dhcp client
you're right but i forgot to say that my client acts like a router. i mean
none of interfaces should have ip address in same range (this is conflict
for me). i can manage each interface to get ip address from DHCP or
manually. so one interface may get ip address from dhcp server whereas all
others have ip addresses which are set manually.
for this situation, do you have any ideas to avoid ip conflict?
thanks again for your attention
On Thu, Jul 11, 2013 at 3:06 PM, Eugene <genie at geniechka.ru> wrote:
> Hi Sam,
> Actually I think this is wrong approach. Correctly configured networks
> should be consistent and should not need such 'fixes'. Also you should
> observe the IP provided by upstream DHCP server otherwise it is an
> invitation for trouble (both technical and possibly legal).
> Are the 'other' interfaces in your internal networks? Then you should
> change them to use different address block from that used in your
> provider's network (there are many address blocks for private networks).
> And/or you should talk to your admin and discuss the address policy, maybe
> they can give you a fixed address.
> Best wishes
> -----Original Message----- From: s m
> Sent: Thursday, July 11, 2013 2:19 PM
> To: freebsd-questions
> Subject: prevent ip conflict in dhcp client
> hello all
> i have a question about dhcp client. i want to know if there is any way to
> understand the ip address which is offered by server before it assigned to
> the interface.
> i have a freebsd system which one of its interfaces should get ip address
> from dhcp server whereas other interfaces have ip addresses and their ip
> address change many times. so i want to prevent ip conflict. is there any
> way to prevent ip conflict in this situation?
> i think the best way is to know the ip address which is offered by dhcp
> server before assigning it to interface and check if it has conflict with
> others or not. is it possible? if yes, how i can do this?
> any comments or hints are appreciated.
> thanks in advance
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