[ntp:questions] NTP over redundant peer links, undetected loops

Richard B. Gilbert rgilbert88 at comcast.net
Tue Feb 17 03:38:43 UTC 2009

Ryan Malayter wrote:
> On Mon, Feb 16, 2009 at 4:13 PM, Dave Hart <davehart at gmail.com> wrote:
>> when it comes up my local IP stack has a problem.  You see, my network
>> at home is also in the ever-popular 192.168.1.x subnet.  Every time I
>> try to send a packet to my desktop machine at, my IP
>> stack tries to deliver it to some other hotel NAT cesspool customer,
>> and the packet never makes it to the VPN.  There are a million
>> variations possible.  Build a B2B link between two companies whose
>> network architects didn't plan in advance for that scenario.
> We generally use randomly selected 10.X.X.X subnets for private
> addresses, which tend to avoid such issues. In fact, we've never had a
> user or partner with conflicting IP space issues on a VPN since we
> switched to that scheme almost ten years ago. Everyone seems to use
> something in the space, so we just don't ;-).

This won't solve the OP's problem as I understand it.

RFC-1918 prescribes three address families for private networks:

The problem is essentially the same for any of the three families.
These address families are not routeable.  Thousands of private networks 
can use the same set of addresses BECAUSE they are not routeable.

A N.A.T (Network Address Translation) capable router lets RFC-1918 
addresses access the Internet by mapping to a valid IP address and port.
The router has ONE external address and 65535 ports available.  The 
router can map non-routeable adresses and ports to routeable addresses 
and ports.

My little home network has three PC's running W/2k or W/XP, one PC 
running Linux, two DEC Alphastations running OpenVMS, three Sun Ultra 10 
workstations running Solaris, a small Cisco 1548M eight port switch and 
a LinkSys BEFSR81 router and eight port switch.  All this stuff uses 
This gives me, potentially, 254 usable but non routable addresses.  The 
ONE routeable address belongs to the internet facing port of my router.

All of this stuff can access the outside world if I need it to.  The 
router maps each inside address and port to a port on the one and only 
routeable address.

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