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Lecture 9

Overlay Networks

Goals of Today’s Lecture

• Motivations for overlay networks

– Incremental deployment of new protocols

– Customized routing and forwarding solutions

• Overlays for partial deployments

– 6Bone, Mbone, security, mobility, …

• Resilient Overlay Network (RON)

– Adaptive routing through intermediate node

Overlay Networks

Focus at the application level

IP Tunneling to Build Overlay Links

• IP tunnel is a virtual point-to-point link

• Illusion of a direct link between two separated nodes

• Encapsulation of the packet inside an IP datagram

• Node B sends a packet to node E
• … containing another packet as the payload

A B E^ F

tunnel

Logical view:

Physical view:

A B E^ F

Overlay Networks

 A logical network built on top of a physical network

 Overlay links are tunnels through the underlying network

 Many logical networks may coexist at once

 Over the same underlying network

 And providing its own particular service

 Nodes are often end hosts

 Acting as intermediate nodes that forward traffic

 Providing a service, such as access to files

 Who controls the nodes providing service?

 The party providing the service

 Distributed collection of end users

Overlays for Incremental

Deployment

6Bone: Deploying IPv6 over IP

A B E F

IPv6 IPv6 IPv6^ IPv

tunnel

Logical view:

Physical view:

A B E F

IPv6 IPv6 IPv6^ IPv

C D

IPv4 IPv

Flow: X

Src: A

Dest: F

data

Flow: X

Src: A

Dest: F

data

Flow: X

Src: A

Dest: F

data

Src:B

Dest: E

Flow: X

Src: A

Dest: F

data

Src:B

Dest: E

A-to-B:

IPv

E-to-F:

IPv

B-to-C:

IPv6 inside

IPv

B-to-C:

IPv6 inside

IPv

Secure Communication Over Insecure Links

• Encrypt packets at entry and decrypt at exit
• Eavesdropper cannot snoop the data
• … or determine the real source and destination

IP Multicast

 Multicast

 Delivering the same data to many receivers

 Avoiding sending the same data many times

 IP multicast

 Special addressing, forwarding, and routing schemes

 Pretty complicated stuff (see Section 4.4)

unicast multicast

MBone: Multicast Backbone

• A catch for deploying multicast

• Router vendors wouldn’t support IP multicast
• … since they weren’t sure anyone would use it
• And, since it didn’t exist, nobody was using it

• Idea: software implementing multicast protocols

• And unicast tunnels to traverse non-participants

Case Study:

Resilient Overlay Networks

RON: Resilient Overlay Networks

Premise: by building application overlay network, can increase

performance and reliability of routing

Two-hop (application-level)

Berkeley-to-Princeton route

application-layer

router

Princeton

Yale

Berkeley

UNR

RON Adapts to Network Conditions

Start experiencing bad performance

Then, start forwarding through intermediate host

A

C

B

RON Customizes to Applications

VoIP traffic: low-latency path

Bulk transfer: high-bandwidth path

A

C

B

bulk transfer