Re: Support for ICMP Time Exceeded in REJECT target ?

[Laurent Pinchart <laurentp@cse-semaphore.com>]

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On Thursday 10 January 2008 09:38, Gáspár Lajos wrote:
> Laurent Pinchart írta:
>
> ...
>
> > I know that my application breaks the OSI model and creates some kind of
> > hybrid "layer 2.5" device. I'm open to suggestions regarding a better way
> > to implement bridges enumeration between two ethernet hosts, but using
> > the traceroute command is a customer requirement which could only be
> > changed with strong valid reasons.
>
> I'm really curios why would anyone need to enumerate the bridging host?
> Could you explain?

Our customer needs IP connectivity between two computers in the engines at 
each end of the train. Each carriage will have an embedded routing device, 
and connecting the carriages together creates a chain that ensures IP 
connectivity.

The customer's application requires enumerating the carriages. One easy 
solution was to enumerate the routing devices in the chain, either using 
their MAC or IP address. Configuring the devices as layer 3 routers would be 
really complex, as all routing tables must be automatically updated whenever 
a carriage is added or removed. Using layer 2 bridges is much easier, but we 
then loose layer 3 route tracing. This is why we thought about making some 
kind of hybrid device that acts as a layer 2 bridge except that it decrements 
the IP TTL and sends an ICMP Time Exceeded message when the TTL reaches 0.

Best regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

Chaussée de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75

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