On Sun, Nov 23, 2008 at 8:25 PM, Brian E Carpenter <[EMAIL PROTECTED]> wrote: >> The third draft is now available at >> http://bill.herrin.us/network/rrgarchitectures.html . > > Looking at Strategy B, I have two comments. > > One is that > "Assign multiple LOCs to each host such that in the network > topography hosts appear as stubs in multiple locations..." > appears to me to be quite clearly the *standard* model for > IPv6, a.k.a. Plan A, so I would suggest inverting the names > of Strategy A and Strategy B.
Hi Brian, Neither strategy A nor strategy B are reflected within the standard model for IPv6. Some specific differences between standard and strategy B: 1. In strategy B, communication sessions survive the loss of any of the locators. This is a new requirement on layer 4. Neither TCP nor any of the common UDP protocols handle this. The dynamic map updates serve two purposes: first to let the remote endpoints know that a new set of locators is available to reach you and second as a lightweight authentication mechanism so that the remote endpoint knows which locators are valid as sources in the packet. 2. In strategy B, locator assignment is dynamic. Not just automatic and not just on the LAN. It starts at the first service provider in the core and dynamically propagates hierarchically down to you with each router receiving the block of addresses from an "upstream" router, assigning subblocks "downstream" and swapping peer routes laterally. As a result, ** the network often adjusts to a edge-network link failure by propagating a new set of locators (layer-3 addresses) downstream and expiring the old ones, ** an approach that retains the hierarchic aggregation of the locators regardless of the current network topology. Note that this requires the impacted hosts to dynamically update their respective map entries. Also as a result, hosts require layer-4 protocols capable of dealing with multiple layer-3 addresses (locators) in each communication stream. 3. In strategy B, a route has to match both the source and destination. This enforces the hierarchy. A route source and destination can't both be 0/0. Announced coreward, 0/0->Dest/long. Announced hostward, Dest/long->0/0. Announced laterally, Source/long->Dest/Long. Thus your packet automatically goes out the correct service provider for the selected source locator. While this is possible with a number of IPv6 implementations it is not a standard part of the architecture and not a requirement. Would you suggest changes to the strategy B description that make this more clear? > 1. There's no problem with transport protocols as long as the > IP stack conceals the address dynamics from the upper layer. Yeah, there is. Sessions don't survive the loss of a layer-3 address and start slow when one of the addresses isn't available. As a result, simple multihoming still has to be carried in the core. SHIM6 and SCTP try to tackle the problem and one or the other may be a viable connection-oriented layer-4 protocol in a strategy B network. I personally think that with the right selection of layer-3 semantics we can do better. Regardless, we'll also need to address the problem for connectionless (UDP-based) protocols. Regards, Bill Herrin -- William D. Herrin ................ [EMAIL PROTECTED] [EMAIL PROTECTED] 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004 _______________________________________________ rrg mailing list [email protected] https://www.irtf.org/mailman/listinfo/rrg
