> -----Original Message----- > From: Arifumi Matsumoto [mailto:arif...@nttv6.net] > Sent: Monday, January 18, 2010 3:26 AM > To: Dan Wing > Cc: 'IETF IPv6 Mailing List'; "'Rémi Denis-Courmont'"; > draft-ietf-6man-addr-select-...@tools.ietf.org; > draft-ietf-6man-addr-select-considerati...@tools.ietf.org; > 'Mohacsi Janos'; 'Fred Baker'; > draft-arifumi-6man-addr-select-confl...@tools.ietf.org > Subject: Re: Discussion summary and next-step Re: Thoughts on > address selection > > Dan, > > thank you for your comments. > My responses below. > > >> > >> Hi, > >> > >> let me summarize the discussion we had about address selection, > >> and move on to the next-step. > >> > >> The discussion was about a try-and-error based mechanism proposed > >> by Fred Baker, and the address selection design team's proposal, > >> which is based on policy distribution. > >> > >> > >> * Fred's proposal. > >> - A host tries each pair of src and dst addresses to establish > >> a connection in a short time period. > >> - A host can make use of ICMP error messages indicating that the > >> src address should be this, or the src address is simply wrong. > >> - A host can have cache for the reachability status, which stores > >> which src and dst pair should be used to reach a certain dst. > >> > >> ** Pro > >> - A connection can be established as far as one working > pair exists. > >> - Routing status can be reflected to address selection directly, > >> which means no need for intermediate agent and information > >> conversion. > > > > Missing a Pro that I consider significant: > > > > - Users will no longer experience multi-second connection > delays due > > to IPv6's address selection. This means more users will > > leave IPv6 enabled. > > not due to IPv6's address selection, but due to IPv6 connection > failure, aren't they ?
The connection failure is caused by incorrect address selection. I don't see how to separate the two. And users don't care -- they simply disable IPv6 if it slows down their experience. > >> ** Con > >> - Impact for host protocol stack implementation. > >> - Not a small change for the existing protocol stack and possibly > >> applications. > > > > It's really the applications that have to change so that they > > are more aggressively going through the getaddrinfo()-sorted > > addresses to get a connection established. > > > >> - We do not have established caching algorithm. > > > > Not a problem caused by, or limited to, Fred's proposal. > Ignoring Fred's > > proposal for a second, RFC3484 address selection policies > could be wrong (as > > we all know) and perhaps they should be able to > learn/notice failures. > > This is what I meant by the combination with Fred's proposal and > policy distribution. > > Of course, it is beneficial to have this combination, but > such caches are not essential for policy distribution way. > > >> - Caching does good for static environment, and can harm for > >> dynamically changing environment. > >> - Network outage invokes cache reconstruction. > >> - Conformance with network policy, user experience. > >> - A connection success does not mean conformance with site network > >> policy, nor user experience, such as delay and bandwidth. > >> - A site may have demands for preference control on address > >> selection, > >> such as IPv6 and IPv4 prioritization, in order to > decrease network > >> provisioning cost or to enhance user experience. > >> - Extra load for network and host. > >> - routers have to send error messages. > >> - servers are loaded by unused sessions. > >> - extra CO2 emission ;) > > > > That amount of extra traffic is tied to how caching and > dynamic learning might > > be specified. We could, if this is a sensitive issue, > specify that things > > work as slowly as today (e.g., multi-second second > connection timeouts before > > trying another IP address). However, this creates a very > poor user experience > > which today can only be resolved by the user disabling > IPv6! We do not want > > people disabling IPv6 to improve their user experience, but > that is their only > > choice today. > > There are so many reasons that makes users disable IPv6, such as > network unreachability, and application IPv6 related > mal-functioning,... > This proposal does not solve all the cases. I am hoping to reduce reasons that users might disable IPv6. > >> - Non-connected transport protocol complexity > >> - Only applications know the connection success/failure > if they use > >> non-connected transport protocol like UDP. > > > > Not a problem caused by, or limited to, Fred's proposal. > > I cannot get why. > > If the kernel caches address selection information, it > has to have connection success/failure information. Yes, and that works even for UDP: a. the OS can see an incoming UDP response packet, because almost every protocol is a request/response protocol or: b. the OS can see the application gave up on one socket and is trying another socket. This indicates the application was -- for whatever reason -- 'displeased' with the address selection made by the OS. (b) seems implementable in the OS, and seems appealing. -d > OTOH, if the appropriate policy is distributed, every > application/protocols can make use of it. > > > > >> - Spoils DNS round-robin based load balancing > >> - Network side(routers) cannot have effects on dst address > selection. > >> Only can have effects on src address selection. > >> > >> > >> * Design Team proposal. > >> - Network side distributes address selection policy to hosts. > >> > >> ** Pro > >> - No impact on protocol stack, as far as it implements RFC 3484. > >> - At least, network policy can be implemented. > >> This does not always lead to user experience enhancement. > >> - Network side can have effects on dst address selection also. > >> ** Con > >> - Hosts have to have functionalito for receiving and > processing policy > >> information. > >> - To make use of routing information, routing information has to be > >> converted to address selection policy at intermediate nodes, and > >> frequently updatable policy distribution mechanism is necessary, > >> such as DHCP reconfigure. > >> > >> > >> * Considerations towards next-step > >> Design team proposal and Fred proposal have different applicability > >> domains, and one does not include the other. > >> Fred proposal works more nicely if combined with Design > >> team'smechanism. > >> Design team proposal can work by itself, but if combined with > >> Fred proposal, the applicability will be broader. > >> So, my suggestion is to have both mechanisms, while keeping > >> one mechianism work without the other protocol. > > > > Sounds alright. > > > > -d > > -- > Arifumi Matsumoto > Secure Communication Project > NTT Information Sharing Platform Laboratories > E-mail: arif...@nttv6.net > -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------