[rbridge] Hop Count processing
Dinesh G Dutt
ddutt at cisco.com
Mon Jun 1 08:46:41 PDT 2009
When I send a unicast traceroute, I put in an address of the egress
Rbridge I expect is the final destination (known by looking at my local
MAC table, for example). Then, why do I have a problem ? I guess I don't
understand what you're saying below,
Joe Touch wrote:
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> Dinesh G Dutt wrote:
>> Using regular frames was my intention. Since end stations are not
>> invlved, I can test actual customer frame and thereby know the exact
>> path for a frame.
> That won't work as per below.
>> Joe Touch wrote:
>>> Why is that useful for traceroute?
>>> (I'm guessing that one of you thinks that we can get away without a
>>> "ping" message, i.e., that we can trace regular packets. That won't
>>> work, however, if the egress rbridge has more than one egress address,
>>> as I discussed.)
>> Do you mean for multi-dst addresses ?
> I believe I can have an rbridge that sits on two different ethernet
> segments, i.e., that has two different egress addresses.
> When I get something with hopcount=0, I respond back with an "error
> hopcount exceeded". I need to pick one of the egress tags to use as the
> message source address. I'm presuming I pick the "canonical address" of
> that rbridge, for which there would be only one.
> Consider a frame sent to the non-canonical egress. You would receive
> back a sequence of error messages:
> Now one of two things has happened. Either the last rbridge was the
> correct one that decapsulated the packet, or it wasn't. The received
> source address of the error message will not match in both cases.
> So how do you know you reached the last hop?
> Why is it even important to be able to do a traceroute with a regular
> packet? Why not just require something like PING, i.e., a TRILL message
> that, once received at the destination address in the TRILL header,
> responds with a "success" response?
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