[PLUG] Odd ping response behavior from private IP addresses

[Shannon C. Dealy]

On Sat, 3 Aug 2002, Matt Alexander wrote:

> On Fri, 2 Aug 2002, Shannon C. Dealy wrote:
>
> > I think you are misunderstanding what is going on here, the "time to live
> > exceeded" means that the packets were being routed, but weren't able to
> > reach their destination within the maximum number of hops that were
> > specified by your computer when the packets were created (quite likely
> > because there is no such destination), sometimes, depending on how the
> > routers are (mis)configured, your packet may simply play ping-pong among
> > the routers until the TTL is exceeded and a response is generated back to
[snip]
> Gotcha.  So, I'm assuming that one box has a route setup for 172.16.1.5,
> for example, that points to the other box, but the other box has the same
> route pointing back to the first box?

Possibly, though I think it's more likely they each have a default routing
configuration that in essence says something like: if I don't have a
defined route for a given IP address/block, send it to router "x" in
case it has one.  Router "x" may in turn send it to router "y" and so on
through all the routers in a continuous loop over and over until the TTL
is exceeded.  Of course if there are only two routers, they would just
bounce it back and forth.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                      |    Embedded Systems, Real-time, Device Drivers
Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
   or: (541) 451-5177 |                  www.deatech.com