1 wjchun@etri.re.krCopyright ETRI

Compact Routing in

LOC-ID Mapping System

전우직wjchun@etri.re.kr

2 wjchun@etri.re.krCopyright 2010 ETRI

Routing: Theory Problem

Consider the following distributed view of shortest path routing on an n node network:

u

e1

e2

e3

V e2

t

T(u)

T(t)

Space: size of table

Stretch : length of path

v

3 wjchun@etri.re.krCopyright 2010 ETRI

Major causes of scalability problems

The Internet is: large and growing

dynamic and more dynamic

Address de-aggregation lots of reasons

most of them are well-documented

Extreme form of de-aggregation All IPv[46] addresses need to be represented as

individual nodes of the global Internet topology graph

4 wjchun@etri.re.krCopyright 2010 ETRI

Extreme forms of aggregation

Trees

Grids

The Internet is neither a tree or a grid

But the Internet is ….

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Compact Routing

Generally, there are too many aspects/tradeoffs. Some of these tradeoffs are quite well understood in theory, others not at all.

A trade-off which is well understood is known as compact routing:

For general (static) graphs it was shown that a stretch strictly below 3 cannot be achieved unless routing tables are at least linear in the number of nodes (in the worst case).

So what about more realistic graphs

Routing Table Size vs. Routing Stretch

6 wjchun@etri.re.krCopyright 2010 ETRI

Compact routing (CR)

problem formulationgiven

graph G (so is its metric space!)findmap (routing function): (s, t) → ps s is a source (or current node), t is a target, ps is a port

at s on the path to t such that routing table size (memory space) and path

lengths (stretch) are nicely balanced

a routing scheme is said to be compact the address and header sizes grow logarithmically routing table size grows sub-linearly path stretch is bounded by a constant.

Stretch of a path a ratio of the longest path produced by a routing algorithm to

the shortest path available

7 wjchun@etri.re.krCopyright 2010 ETRI

Compact routing (CR)

name-dependent (ND) routing can rename nodes as needed (e.g., injecting

some topological information into node names) in order to make routing easier

name-independent (NI)nodes names are also given (e.g., from a flat space)

and cannot be changed Name – address mapping

8 wjchun@etri.re.krCopyright 2010 ETRI

Universal Compact Routing: Landmark

Define a cluster of nodes Direct routing inside the cluster Shortest paths are known

Landmark node elected for each cluster Each node maintains routing paths for all nodes inside its cluster Accurate route to all landmarks Association of each node to its cluster (landmark)

Logical Cluster

Landmark

9 wjchun@etri.re.krCopyright 2010 ETRI

Universal Compact Routing: Landmark

Within a logical cluster, store exact shortest path routing information for all neighborhood nodes

Outside store routing information to all landmarks route through a destination’s closest landmark,

and then route from landmark to destination.

Cluster

u

L(v)

v

Stretch bound follows from the triangle inequality:

Suppose d(u,v) >= d(L(v),v)Then d(u,L(v)) + d(L(v),v)

<= d(u,v) + d(v,L(v)) + d(L(v),v)<= 3d(u,v)

10 wjchun@etri.re.krCopyright 2010 ETRI

Constraints on Landmark Routing

So far: Compact Routing is Static Routing table setup is centralized

require full knowledge of the network graph presume the existence of separate topology discovery

mechanisms

topology changes compact routing needs to be restructured and the balance between the landmark set and clusters

need to be re-established

In small networks the benefits do not provide sufficient gains to overcome the cost of introducing a new routing scheme requires substantially large base to start with

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Mapping Systems for ID-Loc Separation

To circumvents the constraints the mapping system as overlay on top of the BGP

based core BGP provides the topology discovery functionality ID-Loc separation creates an indirection that can

absorb the topological changes

How to utilize Mapping System for CR the network topology creation by assigning mapping

servers either to be part of cluster or landmark set. The map servers reside in the RLOC space and form a BGP/GRE overlay network that

distributes the EID prefixes propagate shorter reachability announcements in the

overlay BGP

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Landmark Map Servers

Landmark Map Servers

(BGP/GRE overlay)

MS MS

MS

MS

MSMS

xTR

xTR

xTR xTRxTR

xTR

Cluster Head

The same RLOC of map server The same RLOC of map server

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Clustering

Cluster of neighboring nodes formed from all xTRs registered at the same MS

can aggregate EIDs allocated as a consistent blocks to strong requirement

share the routing information within the cluster

Role of MS either cluster or landmark based on capability

Sharing mapping within a cluster according to compact routing principles

ensure bounded stretch

matter of local optimization

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Landmarks

Selection of Landmarks MSs advertise reachability aggregate (EID-prefix)

Based on the received advertisements form other MSs MS selects a landmark for its EIDs

A Map Server acts as a landmark by itself aggregation is only for xTRs in the cluster

Choose another MS as its landmark the MS is better positioned

select higher degree nodes to landmarks Not easily known

further study (in BGP advertisements .. )

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Landmarks

After forming Cluster and Selection of Landmarks cluster head MS downloads the list of landmarks

associated EID-prefix/EID into ITRs

Now, ITR has list of landmarks means to associate the EID with the landmarks can send packets(map requests) directly to the

landmarks

Local optimization Large set of information

EIDs associated with landmarks RLOC

Hash, Bloom Filter can be used

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Summery

MSs propagate locators in routing announcements

Landmark propagates a landmark for a block of EIDs

MS can send map register and deregister messages

MS should select cluster heads and landmarks

based on how well they can aggregate EIDs

Optional optimization

MS shares all its mappings with the xTRs

locator of landmarks with associated EID block are downloaded to ITRs

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Gains

Minimize routing table size at the system level (map server) clear upper bound for routing stretch

Organize the MS based on EID numbering space minimize the administrative overhead

Availability and Robustness of overall routing system because of potential to use of multiple MS

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Critique

Not a complete solution Improve a mapping overlay structure, BUT… CRM-modified ALT structure would still be a global query

server system roles of particular nodes in the network being

dynamically assigned concerns about individually owned nodes performing

work for other organizations

Do we need global scale query servers? if yes, do we have any better solutions? Distributed

Servers

Question CRM(landmark), get along with LISP mapping servers? automatic cluster setup or administration ?

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Conclusion & Discussion

On compact routing ? Optimization (Balance) between Memory and Stretch

Too simplified ???

Average case or Worst case analysis Topology change

reconstruct the table

Proactive routing Reactive routing

On landmark universal compact routing

how to build cluster and landmark

different intra- & inter cluster addressing(routing) a challenging problem

LISP and Mapping Server ID-address separation Hierarchy of Cluster