How to detect cycle in a network?

How to detect cycle in a network. suppose
3 routers are directly connected in a triangular manner.
If packet comes to r1, it should forward the packet to the destination
throug r2. Due to some problem, r2 forwards it to r3, r3 to r1 and the
loop continues.
First how to detect this problem, how to correct it and how to
inform the source about the problem.

Ganesh Kundapur wrote:

> How to detect cycle in a network. suppose
> 3 routers are directly connected in a triangular manner.
> If packet comes to r1, it should forward the packet to the destination
> throug r2. Due to some problem, r2 forwards it to r3, r3 to r1 and the
> loop continues.
> First how to detect this problem, how to correct it and how to
> inform the source about the problem.

I'd be very suspicious of a sequence of packets identical other than their
declining ttl's

"Ganesh Kundapur" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> How to detect cycle in a network. suppose
> 3 routers are directly connected in a triangular manner.
> If packet comes to r1, it should forward the packet to the destination
> throug r2. Due to some problem, r2 forwards it to r3, r3 to r1 and the
> loop continues.
> First how to detect this problem, how to correct it and how to
> inform the source about the problem.

If you have packets traversing 3 routers like this, then you have 3 separate
asymetric routing tables that
are combining to form a pump.

In short, this is a human introduced error, and would _have_ to be
deliberate.

T
>

Ganesh Kundapur wrote:

> How to detect cycle in a network. suppose
> 3 routers are directly connected in a triangular manner.
> If packet comes to r1, it should forward the packet to the destination
> throug r2. Due to some problem, r2 forwards it to r3, r3 to r1 and the
> loop continues.
> First how to detect this problem, how to correct it and how to
> inform the source about the problem.

Exactly what Terry said; to *prevent* this you run a routing protocol on
each router that does split horizons (for example).

What you want is a routing procedure that ignores updates from a router that
is already known not to have a correct route to a certain segment.

But in a properly configured network this situation will indeed not occur
naturally.

--
Jeroen Geilman

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