[dhcwg] RE: AD Review Comments On: draft-ietf-dhc-dna-ipv4-09.txt
"Bernard Aboba" <bernard_aboba@hotmail.com> Sun, 20 March 2005 23:11 UTC
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From: Bernard Aboba <bernard_aboba@hotmail.com>
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Date: Sun, 20 Mar 2005 07:37:39 -0800
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Cc: townsley@cisco.com, dhcwg@ietf.org
Subject: [dhcwg] RE: AD Review Comments On: draft-ietf-dhc-dna-ipv4-09.txt
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>(1) Could you explain why sending an ARP request to the default gateway(s) >of the MLPA (as described in section 2.2) is a better mechanism to confirm >what IPv4 configuration parameters should be used than re-initiating DHCPv4 >and/or attempting to renew the DHCPv4 lease (as described in section 2.3)? DNA is an optimization technique. Where hints can "reliably determine" that the host has remained on the same subnet, an ARP Request/Response exchange with the default gateway can be completed more quickly than a DHCPv4 exchange with a DHCPv4 server that might be located off of the local network. Note that if the host has in fact moved to a different subnet, then DNA can actually take longer than DHCPv4, since DNA will incur a timeout when the default gateway does not answer the ARP Request. So the reliability of the hints is in practice quite important, as discussed in Appendix A.1. >Has there been some analysis and/or empirical testing that shows that this >mechanism produces superior results? Appendix A.1 analyzes the conditions under which DNA will produce better results. Schemes similar to DNA have been shipping for several years now, and where the host changes subnets infrequently, the benefits are substantial (e.g. savings of 20 - 100 ms). >(2) Is it assumed that the host would not send any non-DNA-related IPv4 >traffic using its presumed address on the MPLA during the reachability test >and address acquisition phases? If so, would it make sense to state that >restriction here? I don't think this assumption is required. If the lease is still valid, sending packets prior to completion of DNA cannot result in an address conflict, and MAC learning needs to occur anyway. If the host is in fact on the MLPA and the configuration is valid, then sending the traffic is ok. If not, then the packets will not elicit a response, but sending has no worse effect than an address change. For example, if we are talking about VOIP traffic, the additional delay of DNA timeout + DHCP would probably be sufficient to cause the packet to arrive too late anyway, so the host might as well send it. If we are talking about TCP traffic, then an address change would force connection teardown, at which point the additional loss would become irrelevant. >Do you expect that packets would be queued until the address status is >resolved? Or that upper layers would receive errors consistent with an >interface that has not addresses configured? I don't believe it is necessary to queue packets pending completion of DNA, only pending receipt of an L2 "link up" event. From the point of view of the host, if DNA is successful and the host confirms its existing IP configuration, there was no point during which the IP configuration became invalid; the host was attached to the same network all along. An error message is only required if the configuration changes. _______________________________________________ dhcwg mailing list dhcwg@ietf.org https://www1.ietf.org/mailman/listinfo/dhcwg
- [dhcwg] AD Review Comments On: draft-ietf-dhc-dna… Margaret Wasserman
- [dhcwg] RE: AD Review Comments On: draft-ietf-dhc… Bernard Aboba