Sorry, the .txt version. ---------- Forwarded message ---------- From: Charrie Sun <charrie...@gmail.com> Date: 2010/1/20 Subject: Re: [rrg] Fwd: Critique of GLI-Split To: me...@informatik.uni-wuerzburg.de, RRG <rrg@irtf.org>
I revised my critique about GLI-Split, after the discussion with Dr. Menth and have some new understanding on the proposal. Appreciate more for comments and revisions. Best wishes, Letong
Critique of GLI-Split, by Sun Letong GLI-Split makes a clear distinction between two separation planes: the separation between identifier and locator, which is to meet end-users needs including mobility; the separation between local and global locator, to make the global routing table scalable. The distinction is needed since ISPs and hosts have different requirements, also make the changes inside and outside GLI-domains invisible to their opposites. A main drawback of GLI-Split is that it puts much burden on hosts. Before routing a packet received from upper layers, network stacks in hosts firstly need resolve the DNS name to an IP address; if the IP address is GLI-formed, it may look up the map from the identifier extracted from the IP address to the local locator. If the communication is between different GLI-domains, hosts may further look up the map from the identifier to the global locator¡ª the local mapping system forwarding requests to the global mapping system for hosts is just an option. Though host lookup may ease the burden of intermediate nodes which would otherwise to perform the mapping lookup, the three lookups by hosts in the worst case may lead to large delays unless a very efficient mapping mechanism is devised. The work may also become unpractical for low-powered hosts. On one hand, GLI-split can provide backward compatibility where classic and upgraded IPv6 hosts can communicate, which is its big virtue; while the upgrades may be costly to against hosts¡¯ enthusiasm to change, compared to the benefits they would gain. GLI-split provides a way to do multipath routing, while the cost is more burdens placed on hosts. However, this tradeoff between costs and gains exists in most proposals. For mobility GLI-Split does not update DNS data when GLI-hosts move across GLI-domains, mainly for communications with classic IPv6 hosts, and leaves the communication patterns supported by mobile IP. I think the DNS updates can be changed a little, to allow both home address and current global locator of GLI-mobile-node to exist in the DNS data. GLI-corresponding-nodes can query DNS and get the real-time global locator of the GLI-mobile-node, thus need not query the global mapping system again (unless it wants to do multipath routing, of course). The question of whether DNS updates can catch up with node movements is resoluble. On one hand, DNS data updates only when GLI-hosts move across GLI-domains, which is much less frequent compared with host mobility within a GLI-domain; on the other hand, small caching time of DNS (now a few seconds or minutes for load balance and other applications) and the updates triggering mechanism can make DNS data updates in time. This modification in DNS updates could bring more benefit for GLI-nodes, further encouraging classical nodes to upgrades.
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