Routing in Multi-Layered Networks

Srinivasan SeetharamanGeorgia Institute of Technology

srini@cc.gatech.edu

Case Western Reserve UniversityMarch 2007

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Internet ArchitectureCurrent Internet architecture has been guided by the end-to-end principle:

network layer implements simple primitives useful for a broad range of end-to-end applications for good balance between cost vs benefit

33

Internet EvolutionA survey of Cisco router software features…

Feature Year VersionFault restoration 1986 SSR 1Multicast 1994 IOS 10.2DiffServ prioritization 1997 IOS 11.0Tag switching (pre-MPLS) 1997 IOS 11.1Security – 1: Encryption, Firewalls

2000 IOS 11.2

Security – 2: NAT 2001 IOS 12.0No dramatic change in services offered to end-user

2007 IOS 12.4T

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Internet Evolution (contd.)Common observations:

Core features are gradually beginning to ossify Routers are becoming faster and more reliable

Deployability concerns are common with most services

All-or-nothing implementation problems For example, we still do not see deployment of Secure-

BGPNeed for ways to offer new services and enhance existing services!

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Overlay NetworksOverlay networking helps overcome functionality limitations by forming a virtual network that is:

Independent Customizableover the IP network (Native layer).

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Overlay routing is independent of native layer routing Each Overlay path comprises one or more Overlay

links, based on a certain selfish objective

Example: Latency-Optimized Overlay

AD

CB

50ms

20ms

20msRelayin

g

Overlay link Overlay

nodes

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Service Overlay NetworksClassification

Overlay networks

Peer-to-peernetworks

End-systemoverlays

(e.g. Skype)

Routing overlaynetworks

Serviceoverlays

(e.g. VINI)

Multicast (e.g. ESM, Overcast) Better routes (e.g. RON, Detour, X-Bone) Customized forwarding (e.g. I3, Scattercast) QoS (e.g. OverQoS, SON) Security (e.g. DynaBone, SOS)… and much more

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Service Overlay Networks (contd.)

A

D

E F

G

H

FH

GAE

C

C

B

OVERLAYLAYER

NATIVE IPLAYER

D

B

Throughput optimized overlay

Latency optimizedoverlay

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Cross-Layer Interaction

Performing dynamic routing at both layers leads to:

Functionality overlap (Both overlay layer and IP layer perform similar set of functions)

Mismatch or misalignment of routing objectives

Contention for limited physical resources

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Cross-Layer Interaction (contd.)

These issues are amplified in the presence of Selfish motives Lack of information about other layer Increasing impact ( #overlays |Traffic| )

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Overlay routing conflicts with native layer load balancing.- [Infocom07]

Overlay routing can violate inter-domain policies.- [ICNP06]

Failure detected by both layers and rerouted twice, with each rerouting disrupting the optimality of the previous.- [Infocom06]

A framework for improved support of overlay services- [Hotnets05]

Outline of my work

Potential for Indefinite Conflict!

Conflict 1. Intra-domain

Overlay routing vs Traffic Engineering

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Repeated Non-Cooperative GamePlayer1: Overlay Routing - Latency-optimized paths between

nodes

Player2: Traffic Engineering - MPLS-based scheme that solves a linear program (LP) to obtain optimal routes

OverlayRoutingOverlay Link

Latencies

Overlay layertraffic

Overlay routes

TrafficEngineerin

g

Traffic on each overlay

link

Background traffic

Nativeroutes

Native linkdelays

TM

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Illustration of OR vs TE

A

E

I D

F

B H

C

G

A

B

D

C

OVERLAYNATIVE

J

32ms 2ms

3

23ms 3ms2

210m

s10m

s

2

210m

s2ms

4 42ms 3ms

3

42ms

4ms5

36ms 2ms3

4ms

14ms

10m

s

4ms

23m

s

5ms

Initial State

Numbers on each link

represent the avail-bw

Shortest latency routes

Minimize(Max util)

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2

211

0 0

Illustration of OR vs TE (contd.)

A

E

I D

F

B H

C

G

A

B

D

C

OVERLAYNATIVE

J

2ms 2ms

23ms 3ms2

210m

s10m

s

2

210m

s2ms

4 22ms 3ms

42ms

4ms6ms 2ms

4ms

14ms

10m

s

6ms

23m

s

5ms

Overlay traffic

introduced

Multihop paths

A B CA B D

Avail-bw changed

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A

E

I D

F

B H

C

G

A

B

D

C

OVERLAY

NATIVE

J

12ms 2ms

1

13ms 3ms1

210m

s10m

s

2

210m

s2ms

2 42ms 3ms

2

22ms

4ms3

16ms 2ms2

14ms

10m

s

4ms

23m

s

5ms

SPLIT

After TE reacts

Multihop paths

A B CA B D

Latencychanged

Illustration of OR vs TE (contd.)

5ms

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A

E

I D

F

B H

C

G

A

B

D

C

OVERLAYNATIVE

J

12ms 2ms

1

13ms 3ms1

210m

s10m

s

2

210m

s2ms

0 42ms 3ms

0

02ms

4ms5

36ms 2ms0

5ms

14ms

10m

s

23m

s

5ms

SPLIT

After Overlay routing reacts

4ms

Avail-bw changed

Illustration of OR vs TE (contd.)

Multihop pathsA B C

A B C DB C D

2 2

2

3

1 2

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Simulation Results

TEobjective

Overlayobjective

Overallstability

Round

2020

General Approach: Similar to Stackelberg’s game: Designate leader/follower. Make Leader act after predicting (or) counteracting the

subsequent reaction of the follower

Leader undertakes preemptive action such thata. Follower has no desire to change Friendlyb. Follower has no alternative to pick Hostile

Use history to learn desired action gradually.

Resolving Conflict

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Preemptive Strategies: Summary

We proposed four strategies that improve performance for one layer and achieve a stable operating point

Inflation factor= Steady state obj value with strategy

Best obj value achievedLeader Strategy Overlay TEOverlay Friendly: Load-constrained LP

Hostile: Dummy traffic injection1.0821.023

1.1221.992

Native Friendly: Hopcount-constrained LPHostile: Load-based Latency tuning

1.0271.938

1.1841.072

Inflation

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Preemptive Strategies: Summary (contd.)

Each strategy achieves best performance for the target layer

within a few rounds with no interface between the two layers with all information inferred through simple

measurements

Conflict 2. Inter-domain

Overlay routing vs Inter-Domain Policy

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Inter-Domain Policy ViolationsObjective of overlay layer: Offer better latency routes to end-systems

But, what is assumed here? Harvard is not unhappy with relaying overlay

packets

Colorado State Univ

Harvard Univ

Univ of NC

30 ms

24 ms

61 ms

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Provider 1

Inter-Domain Policy Violations (contd.)

A more realistic picture…

Unhappy Money Load

Client 1

A Client 2B

Client3C

Provider 2

Peer

Peer

Legitimate native route

Overlay route

Valley-free violation

$$

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Planetlab Overlay Measurements

Topology:58 geographically distributed Planetlab nodes (Univ + Commercial). This represents 3306 overlay paths

Measurement steps:1. Determine AS path of each overlay link

(Rockettrace / traceroute for hop list + IPAS mapping)2. Determine overlay path based on shortest path algorithm

(For Cost = latency, 56.6% overlay paths prefer relaying)3. AS relationships inferred using Gao’s algorithm

Data: http://www.cc.gatech.edu/~srini/code

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Only multihop overlay paths are violating

Extent of transit policy violations in multihop paths

Measurement Results

Violation Type % pathsProvider-AS-Provider 63.1Provider-AS-Peer 2.4Peer-AS-Provider 2.0Peer-AS-Peer 2.4Total 69.9

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Policy Enforcement by Native Layer

As ISPs become aware of the negative impact of overlays and commence filtering, this leads to

drastic deterioration in overlay route performance commensurate with the number of ASes enforcing policy

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Overlay service provider shares some of the cost incurred by the native layer

For a certain fee, we adopt one of the following strategies for achieving good legitimate paths:

1. Obtain transit permit from certain AS

2. Add new node to certain provider AS

Cost-sharing approach

Resolving Conflict

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With no filtering,

Illustration of Cost Sharing

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21

32

22

11 13

23

33

Cust-Prov relationPeering relation

Transitviolation

AS hosting overlay node

Tier-1 provider

Tier-2 provider

Stub customer

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With filtering, we have no multi-hop paths

Illustration of Cost Sharing (contd.)

31

21

32

22

11 13

23

33

Cust-Prov relationPeering relation

AS hosting overlay node

Tier-1 provider

Tier-2 provider

Stub customer

3333

Option 1: Add new overlay node to provider AS 22

Option 2: Obtain transit permit from stub AS 32

Illustration of Cost Sharing (contd.)

31

21

32

22

11 13

23

33

Cust-Prov relationPeering relation

AS hosting overlay node

Tier-1 provider

Tier-2 provider

Stub customer

22

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In Summary, Overlays…… offer valuable services needed by end-systems

… leads to complex cross-layer interaction with potentially detrimental effects

… are hard to detect, as seen from efforts with identifying Skype traffic

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Ongoing Work

Conflict-aware overlay node placement

Multi-layer testbed using Planetlab-VINI that allows control of multiple layers

Analysis of other “performance-aware” overlays(like Bittorrent)

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Other WorkThere exists other forms of collaboration that are malicious.

I work on exposing their memberships in a scalable manner

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Future of Overlays

Overlays are essential as… Means for end-systems to collaborate Environment for testing future innovations (GENI) Architecture for Future Internet in the form of Network

Virtualization

Cross-layer interaction will affect performance. How best to design protocols and services in the future?

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Future Research – Native Layer

How to prepare ISPs for overlay applications? To promote it To contain it

No effective solution for identifying relayed traffic. Need an orthogonal policy between overlay/native.

Need to address the network impasse. How to tune the network for

.. the new breed of Internet applications? (e.g., file sharing)

…and new paradigms of communication? (e.g., wireless)

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Future Research – Service Layer

How best to support multiple Internets? Researchers suggest a future with multiple coexisting

Internets (Potential outcome of NSF-FIND program) Model as multiple coexisting overlays

Which layer to implement a service at? For example, a service like multicast can be performed at both native layer and overlay layer!

Which layer to use for a particular scenario? Which layer needs optimizing?

Thank you!

See: http://www.cc.gatech.edu/~srini

Questions