Subject: [rrg] Proposal: 2-phased mapping for Internet core/edge split schemes

From: wei zhang <[email-masked]>
Date: Mon, 21 Dec 2009 21:25:26 +0800

Hi,all
I propose a 2-phase mapping scheme which could be used and independent
of any core/edge split mechanism(such as LISP or eFIT etc.).

 The motive: to reduce the dynamic of mapping updates and facilitate
effective mapping look up.

 Considerations:
1.Mapping from prefixes to ETRs is an M:M mapping. Any change of
(prefix, ETR) pair should be updated timely which can be a heavy
burden to any mapping systems if the relation changes frequently.
2.prefix<->ETR mapping system cannot be deployed efficiently if it is
overwhelmed by the worldwide dynamics. Therefore the mapping itself is
not scalable with this direct mapping scheme.

 My contribution: a 2-phased mapping
1.Introduce AS number in the middle of the mapping, phase I mapping is
prefix<->AS#, phase II mapping is AS#<->ETRs. We have a M:1:M mapping
model now.
2.My assumption is that all ASes know better their local prefixes (in
the IGP) than others. and most likely local prefixes  can be
aggregated when map them to the AS#, which will make the mapping entry
reduction possible, ASes also know clearly their ETRs on its border
between core and edge. So all mapping information can be collected
locally.
3.A registry system will take care of the phase I mapping information.
Each AS should have a register agent to notify the local range of IP
address space to the registry. This system can be organized as a
hierarchical infrastructure like DNS, or alternatively as a
centralized registry like "whois" in each RIR. Phase II mapping
information can be distributed between XTRs as a BGP extension.
4. A basic forwarding procedure is that ITR firstly get the
destination AS# from phase I mapper (or from cache) when the packet is
entering the "core". Then it will check the closest ETR of destination
AS#, since phase 2 mapping information has been "pushed" to it through
BGP updates. At last the ITR encap the packet and tunnel it to a
corresponding ETR.

Gains:
1.Any prefixes reconfiguration (aggregation/ deaggregation) within an
AS will not be notified to mapping system.
2.Possible highly efficient aggregation of the local prefixes (in the
form of an IP space range).
3.Both phase I and phase II mapping can be stable.
4.A stable mapping system will reduce the update overhead introduced
by topology change/routing policy dynamics.ETR.

Summary:
1.The 2-phased mapping scheme introduces AS# between the mapping
prefixes and ETRs.
2.The decoupling of direct mapping makes highly dynamic updates
stable, therefore it can be more scalable than any direct mapping
designs.
3.The 2-phased mapping scheme is adaptable to any core/edge split
based proposals.

Wei Zhang