Hi Tim, On 11/3/10 8:00 AM, Thomas Narten wrote: > Hi Tim > >> At the UNH-IOL we recently received a router implementation that >> discards a packet when it receives a packet with a hop >> limit of zero. Based on the following quote from RFC 2460, >> "The packet is discarded if Hop Limit is decremented to >> zero." If router is the end-node it should still process >> the the packet, as the hop-limit isn't decremented until >> the packet is forwarded. > > That is the intended behavior. You only discard a packet if you > decrement the TTL and it reaches zero.
Correct. > >> According to RFC 4443 Section 3.3 "If a router receives a >> packet with a Hop Limit of zero, or if a router decrements a >> packet's Hop Limit to zero, it MUST discard the packet and originate >> an ICMPv6 Time Exceeded message with Code 0 to the source of the >> packet." The UNH-IOL had interpreted router to be a device that is >> forwarding a packet, therefore the packet should still be processed >> when it's the end receiver. The implementation viewed this quote as >> stating that a router should discard the packet regardless of being >> the end receiver. > > This section refers to the generation of a Time Exceeded Message. You > shouldn't be executing this section of the spec unless you had already > decided to generate such a message. (That said, the wording above > could be better.) I agree the wording could be better. I would also note that it is possible that this particular router implementation may have a different design than other routers. Is it possible that the forwarding logic is used generically to move locally destined traffic to the main processor? In this case, the forwarding ASIC still thinks it is routing the packet. > >> So I would like to ask the working group should a router always >> discard a packet with a hop limit of zero even when it's >> the end receiver of the packet? > > IMO, only if it decrements the TTL and it reaches zero. One only > decrements if one is about to forward a packet... > > Also, RFC 2460 says: > >> Hop Limit 8-bit unsigned integer. Decremented by 1 by >> each node that forwards the packet. The packet >> is discarded if Hop Limit is decremented to >> zero. Right. So, is this router under test using a different design that doesn't fit the generic router model used to develop this text? Regards, Brian -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
