The IP over ATM Mailing List Archive by date

[Telford001@aol.com]

In a message dated 96-06-03 02:13:56 EDT, mohta@necom830.hpcl.titech.ac.jp
(Masataka Ohta) writes:

>> With regard to TTL, CSRs, and NHRP - decrementing TTL guarantees that
>> if routing screws ups, packets won't loop forever.

>It is actually a link layer (non-)problem of ATM.

That problem may be better described as a conflict between
link layer and network layer routing.

>> If you have a box
>> that participates in IP routing, but TTL doesn't decrement when
>> packets traverse that box, then a bug in the routing code can result
>> in infinitely looping packets.

>If you have a box
>that participates in PNNI routing, but TTL doesn't decrement when
>cells traverse that box, then a bug in the routing code can result
>in infinitely looping cells. Thus, a true ATM switch
>(with the emphasis on swich) decrement TTL, UNLESS it doesn't
>participate in the PNNI routing algorithm.

This claim certainly is not true unless an extremely unsophisticated
architecture for combining ATM switching and network layer
routing is in use.

>Hmmm, so, ATM lacking TTL, you think ATM switchs shouldn't
>participate in PNNI routing.

>Use Ipsilon.

Ipsilon may not solve any problem.  From reading the trade
rags, the Ipsilon approach to combining ATM switching and
IP routing appears to be fairly unsophisticated, but of course
trade rags are not necessarily the best source of information
on such matters.

>To me, policed ATM is good enough, because a transient loop of
>a flow won't affect other flows.

Now, why should there even be a transient loop of flow?

Joachim Martillo
Father of the VLAN Router
Grandfather of the CSR
President 
Telford Tools, Inc. (TTI)
"Garage Mechanics for the I-Way"
17 Pleasant Hill Ave.
Dorchester/Mattapan, MA 02126-2813
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