bridging 172 networks ?

Simon Hobson dhcp1 at
Sat Aug 25 20:25:53 UTC 2007

Compustretch NewYork wrote:
>A certain host dhcp server (dhcp3d) has been serving up IPs in the
>172.16 range to an internal network.
>This server's upstream has now changed to, also, a 172.16 based network
>Thus one nic is given a address by the upstream server,
>the second nic is handing out leases in the 1.2 to 1.254 range.
>Does one of these networks need to switch to 192 or 10, or can they both
>be on 172?
>If so, what is the best solution to preventing an IP conflict?
>Hoping this question is neither too simple nor too complicated but just

It's lacking in information !

You have an 'internal' network with unspecified subnet mask.

Your 'outside' network has changed from using public IPs to RFC1918 
IPs, again with unspecified subnet mask.

We don't know if you are routing or NATting through the gateway.

We don't know the extent of the addressing schemes.

Taking educated guesses, I'll guess that you were probably NATting 
through the gateway and using /24 subnets. On that basis there is no 
conflict - does not overlap (and it 
doesn't matter if you are natting or routing).

If either network is more extensive than that then you'd have to look 
again. For example, if some idio^H^H^H^Hinexperienced sysadmin used in either network then your have a conflict and would 
have to change something.

But this is a basic IP addressing issue, nothing to do with DHCP. If,, and don't mean anything 
to you then I suggest finding a primer in IP addressing.

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