New Routing Architectures

1
New Routing Architectures

• Jennifer Rexford
• Advanced Computer Networks
• http//www.cs.princeton.edu/courses/archive/fall08
  /cos561/
• Tuesdays/Thursdays 130pm-250pm

2
Outline

• Changing the routing architecture
• Why?
• Where and how?
• Example architectures
• Removing routing from routers
• Hybrid Link-state/Path-vector
• Resilient Overlay Routing

3
Why Change Routing?

• Better performance
• Scalability, security, convergence, reliability,
  flexibility,
• Simpler management
• For network operators
• For folks deploying services
• Greater extensibility
• To enable experimentation
• To enable new services

4
What to Change, and Where?

• Add another layer about network routing
• Routing functionality in overlay networks
• Change the routing protocols
• To improve scalability, security, convergence,
• Change the division of functionality
• Data, control, and management planes
• Change the division of responsibility
• End users, third parties, and service providers
• ???

5
Removing Routing from Routers Routing Control
Platform, Routing as a Service, 4D Control Plane,
Ethane,
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Network Operators

• Network-wide views
• Network topology (e.g., routers, links)
• Mapping to lower-level equipment
• Traffic matrix
• Network-level objectives
• Load balancing
• Survivability
• Reachability
• Security
• Direct control
• Explicit configuration of data-plane mechanisms

7
What Should Routers Do?

• Forward packets yes
• Must be done at high speed
• in line-card hardware on fast routers
• So, needs to be done on the routers
• Collect measurement data yes
• Traffic statistics
• Topology information
• Compute routes no???
• Distributed computation of forwarding tables
• Doesnt inherently need to run on the routers

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Reasons to Remove Routing From Routers

• Routing is hard to do in a distributed fashion
• Beyond single-path and/or shortest-path routing
• Difficult to make load-sensitive routing stable
• Over-reacting to out-of-date information
• Poor visibility to drive good decisions
• Incomplete local views of topology and load
• Not flexible enough for end users
• Cannot easily select customized routes
• Difficult to extend over time
• Hard-coded into the underlying routers

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Routing Control Platform

• Goal Move beyond todays artifacts, while
  remaining compatible with the legacy routers
• RCP computes routes for the routers
• Network-wide visibility and control
• Backwards compatibility
• RCP speaks to routers using BGP protocol

RCP
AS 2
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Example Services

• Selective denial-of-service attack blackholing
• Identify entry point and victim of attack
• Drop offending traffic at the entry point
• Planned maintenance dryout
• Drain traffic off of an edge router
• Before bringing it down for maintenance
• Flexible egress point selection
• Multiple ways to reach the same destination
• Giving customers control over the decision
• Enhanced interdomain routing security
• Anomaly detection or security protocols

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Routing As a Service

• Goal third parties pick end-to-end paths for
  clients to satisfy diverse user objectives
• Forwarding infrastructure
• Basic routing (e.g., default routing)
• Primitives for inserting routes
• Route selector
• Aggregates network information
• Selects routes on behalf of clients
• Competes with other selectors for customers
• End host
• Queries route selector to set up paths

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Feasibility

• Fast reaction to failures
• Routers are closer to the failures
• Can a service react quickly enough?
• Scalability with network size
• State and computation grow with the topology
• Can a service manage a large network?
• Reliability?
• Service is now a point of failure
• Is simple replication enough?
• Security?
• Service is now a natural point of attack
• Easier (or harder) to protect than the routers?

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Improving BGP Convergence
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Routing Change Before and After
0
0
(2,0)
(2,0)
(1,0)
(1,2,0)
1
1
2
2
(3,2,0)
(3,1,0)
3
3
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Routing Change Path Exploration

• AS 1
• Delete the route (1,0)
• Switch to next route (1,2,0)
• Send route (1,2,0) to AS 3
• AS 3
• Sees (1,2,0) replace (1,0)
• Compares to route (2,0)
• Switches to using AS 2

0
(2,0)
(1,2,0)
1
2
(3,2,0)
3
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Routing Change Path Exploration
(2,0) (2,1,0) (2,3,0) (2,1,3,0)

• Initial situation
• Destination 0 is alive
• All ASes use direct path
• When destination dies
• All ASes lose direct path
• All switch to longer paths
• Eventually withdrawn
• E.g., AS 2
• (2,0) ? (2,1,0)
• (2,1,0) ? (2,3,0)
• (2,3,0) ? (2,1,3,0)
• (2,1,3,0) ? null

(1,0) (1,2,0) (1,3,0)
1
2
3
(3,0) (3,1,0) (3,2,0)
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Convergence Overhead and Delay

• Path exploration is expensive
• Large number of possible paths
• Might have to explore (nearly) all of them
• Much slower than link-state routing
• Simply floods the topology
• And routers compute shortest path
• Any way to reduce BGP convergence time?
• Avoid exploring paths with the same failure?
• Hybrids of path vector and link state?

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HLP Hybrid Link-state/Path-vector

• Assume hierarchical AS structure
• Provider-customer relationships dominate
• And some peer-peer edges
• (Are we willing to cook in these assumptions?)
• Hybrid of link state and path vector
• Link state within a sub-tree
• Path vector across peer-peer links
• Route on AS numbers
• Rather than prefixes

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Add New Features in an Overlay Resilient Overlay
Networks
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Overlay Networks
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Overlay Networks
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RON Resilient Overlay Networks

• Premise by building application overlay network,
  can increase performance and reliability of
  routing

Princeton
Yale
application-layer router
Two-hop (application-level) Berkeley-to-Princeton
route
Berkeley
http//nms.csail.mit.edu/ron/
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RON Circumvents Policy Restrictions

• IP routing depends on AS routing policies
• But hosts may pick paths that circumvent policies

USLEC
ISP
Patriot
PU
me
My home computer
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RON Adapts to Network Conditions
B
A
C

• Start experiencing bad performance
• Then, start forwarding through intermediate host

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RON Customizes to Applications
B
voice
A
bulk transfer
C

• VoIP traffic low-latency path
• Bulk transfer high-bandwidth path

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How Does RON Work?

• Keeping it small to avoid scaling problems
• A few friends who want better service
• Just for their communication with each other
• E.g., VoIP, gaming, collaborative work, etc.
• Send probes between each pair of hosts

B
A
C
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How Does RON Work?

• Exchange the results of the probes
• Each host shares results with every other host
• Essentially running a link-state protocol!
• So, every host knows the performance properties
• Forward through intermediate host when needed

B
B
A
C
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RON Works in Practice

• Faster reaction to failure
• RON reacts in a few seconds
• BGP sometimes takes a few minutes
• Single-hop indirect routing
• No need to go through many intermediate hosts
• One extra hop circumvents the problems
• Better end-to-end paths
• Circumventing routing policy restrictions
• Sometimes the RON paths are actually shorter

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RON Limited to Small Deployments

• Extra latency through intermediate hops
• Software delays for packet forwarding
• Propagation delay across the access link
• Overhead on the intermediate node
• Imposing CPU and I/O load on the host
• Consuming bandwidth on the access link
• Overhead for probing the virtual links
• Bandwidth consumed by frequent probes
• Trade-off probe overhead vs. detection speed
• Possibility of causing instability
• Moving traffic in response to poor performance
• May lead to congestion on the new paths

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Future Routing Architecture

• Who is in charge?
• Network administrators?
• End hosts?
• Third-party overlays?
• Third-party routing providers?
• Build on top of todays network?
• New AS-level control plane?
• Overlays on top of existing Internet?
• Assume (restricted) economic models?
• To improve scalability and convergence?