[rbridge] Hop Count processing
touch at ISI.EDU
Wed May 20 07:41:57 PDT 2009
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Donald Eastlake wrote:
> I'm fine with changing hop count processing to make it the same as IPv4
> and IPv6 even it reduce the distance a TRILL encapsulated frame can go
> by 1 hop.
My point is that you're not making it the same as IPv4 and IPv6. We need
to recognize that TRILL ingress and egress devices are NOT forwarders --
they are "hosts"; they do NOT decrement the hopcount, and thus they do
NOT drop packets once received regardless of hopcount.
I.e., either we're going for IP behavior or not...
> On Fri, May 15, 2009 at 12:10 PM, Joe Touch <touch at isi.edu
> <mailto:touch at isi.edu>> wrote:
> James Carlson wrote:
>> Radia Perlman writes:
>>> I suspect nobody will care, so we can just go with Dinesh's wording.
> If the goal is to make this work like IP, the wording needs correction.
> The original proposed wording is:
> The Hop Count field is a 6-bit unsigned integer. It is decremented by 1
> by each Rbridge that forwards a TRILL encapsulated frame. The frame is
> dropped if either the Hop Count in the received frame is 0 or the Hop
> Count is decremented to 0.
> In IP, the following is true:
> " A router MUST NOT discard a datagram just because it was received
> with TTL equal to zero or one; if it is to the router and otherwise
> valid, the router MUST attempt to receive it."
> I.e., the packet is dropped if the TTL is zero or one on receipt only if
> it is forwarded; if it is being 'accepted' (i.e., in this case, if the
> destination is the trill node doing the processing), then a TTL of zero
> is acceptable.
> It seems like the wording needs to include this second case...
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