[e2e] Detecting middle boxes

[David P. Reed]

I got your reply.  I do indeed think it might be interesting to code it up 
and try it.  If anyone does, let me know.  I may get around to it sometime 
if no one else does.

At 01:26 PM 2/11/2002 -0600, John Kristoff wrote:
>I think my reply to David earlier was lost, but I like the idea of
>trying to find ways for the ends to detect middle boxes.  One unoriginal
>idea might be to use traceroute style packets using common middle box
>altering packet types.  So instead of the typical ICMP/UDP traceroute
>packets, use TCP port 25, 53 or 80 packets, increasing the TTL to map
>out the route.
>
>The upper layer protocols and application data can be specially encoded
>so that the detector can discern what may have been altered with the
>resulting unreachable messages.  Obviously the unreachables will only
>alert the detector to what may have changed in the IP datagram plus the
>following 64 bits, but perhaps that is enough?  If the data returned
>differs from one hop to another, you just found a middle box.
>
>However, I suspect for many environments, you wouldn't get the
>unreachables back (e.g. strict firewall policies), which would make this
>technique unusable.
>
>John