Boston Linux & UNIX was originally founded in 1994 as part of The Boston Computer Society. We meet on the third Wednesday of each month at the Massachusetts Institute of Technology, in Building E51.

BLU Discuss list archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Discuss] selecting a subnet

If youe corp network uses addresses in the range, how about
using an address in the range?

Steven Santos
Simply Circus, Inc.
86 Los Angeles Street
Newton, MA 02458

P: 617-527-0667
F: 617-934-1870
E: Steven at

On Wed, Sep 10, 2014 at 11:17 PM, Chuck Anderson <cra at> wrote:

> On Wed, Sep 10, 2014 at 06:59:51PM -0400, Bill Horne wrote:
> > If by "Firewall" you mean Network Address Translation-enabled
> > wired-only router, then it's a non issue. You plug the "WAN" port
> > into your corporate network and set it for DHCP (or whatever fixed
> > address your IT guys assigned to the port).  The router will
> > translate whatever "detached" IP range you choose, e.g.,
> >, and you'll be in business.
> It is not a non-issue if you choose an IP subnet behind the NAT that
> conflicts with the same/overlapping IP subnet somewhere else outside
> the NAT.  For example, consider what would happen if you choose
> as your inside NAT address space.  You wouldn't be able to
> reach Google's nameserver on the Internet at because that
> address would be routed locally by your local hosts, rather that being
> routed out to the Internet.  Now, hopefully no one would be silly
> enough to choose a "public" non-RFC1918 network address for use behind
> their NAT, but the issue is the same if you have a double-NAT scenario
> and you choose an RFC1918 subnet that is already in use anywhere
> outside your NAT (such as inside the outer NAT).  If you happen to
> choose badly, you may not be able to reach some corporate server you
> may need to access.
> I was once visiting a friend who had set up their local RFC1918
> network to use  Unfortunately, this was also the
> default subnet used by Fedora's KVM virtualization stack libvirtd,
> which started up a virbr0 network bridge on the host addressed as
> even if there were no guest VMs at all yet.  Hilarity
> ensued when both wlan0 and virbr0 were configured with the same
> subnet, but weren't actually the same physical network.  Nothing at
> all worked in this "split-brain" scenario.
> _______________________________________________
> Discuss mailing list
> Discuss at

BLU is a member of BostonUserGroups
BLU is a member of BostonUserGroups
We also thank MIT for the use of their facilities.

Valid HTML 4.01! Valid CSS!

Boston Linux & Unix /