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Routing in Multi-Layered Networks
Srinivasan SeetharamanGeorgia Institute of Technology
srini@cc.gatech.edu
Case Western Reserve UniversityMarch 2007
22
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
44
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!
55
Overlay NetworksOverlay networking helps overcome functionality limitations by forming a virtual network that is:
Independent Customizableover the IP network (Native layer).
66
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
77
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
1010
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
1111
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
1515
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)
1616
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
2222
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
2323
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
$$
2727
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
2828
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
3131
With no filtering,
Illustration of Cost Sharing
31
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?
3939
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
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