A Routing Control Platform for Managing IP Networks

1
A Routing Control Platform for Managing IP
Networks

• Jennifer Rexford
• Princeton University
• http//www.cs.princeton.edu/jrex

2
Outline

• Revisiting the control plane
• Complexity of todays control plane
• Principles for a redesign
• Routing Control Platform
• Deployability
• Scalability
• Reliability
• Example applications
• DDoS blackholing, planned maintenance, and
  customized egress selection
• Conclusions and future work

3
Internet Architecture

• Smart hosts, and a dumb network
• Network delivers packets to hosts
• Services implemented on hosts
• Keep most state at the edges

Edge
Edge
Network
IP
IP
But, how should we partition function vertically?
4
Today Inside a Single Network

• Data Plane
• Packet handling by routers
• Forwarding, filtering, queuing

Packet filters
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No State in the Network? Yeah, Right

• Dynamic state
• Routing tables
• Forwarding tables
• Configuration state
• Access control lists
• Link weights
• Routing policies
• Hard-wired state
• Default values of timers
• Path-computation algorithms

Lots of state, updated in a distributed,
uncoordinated way
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How Did We Get in This Mess?

• Initial IP architecture
• Bundled packet handling and control logic
• Distributed the functions across routers
• Didnt fully anticipate the need for management
• Rapid growth in features
• Sudden popularity and growth of the Internet
• Increasing demands for new functionality
• Incremental extensions to protocols routers
• Challenges of distributed algorithms
• Some tasks are hard to do in a distributed
  fashion

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What Does the Network Operator Want?

• 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

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What Architecture Would Achieve This?

• Management plane ? Decision plane
• Responsible for all decision logic and state
• Operates on network-wide view and objectives
• Directly controls the behavior of the data plane
• Control plane ? Discovery plane
• Responsible for providing the network-wide view
• Topology discovery, traffic measurement, etc.
• Data plane
• Queues, filters, and forwards data packets
• Accepts direct instruction from the decision plane

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Advantages of the New Approach

• Lower management complexity
• Complete, network-wide view
• Direct control over the routers
• Single specification of policies and objectives
• Simpler routers
• Much less control-plane software
• Much less configuration state
• Enabling innovation
• New algorithms for selecting paths within an AS
• New approaches to inter-AS routing

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Example Improving ISP Routing

1. Provide internal reachability (IGP)
2. Learn routes to external destinations (eBGP)
3. Distribute externally learned routes internally
   (iBGP)
4. Select closest egress (IGP)

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Is the New Architecture Feasible?

• Deployability any way from here to there?
• Must be compatible with todays routers
• Must provide incentives for deployment
• Speed can it run fast enough?
• Must respond quickly to network events
• Needs to be as fast as a router
• Reliability avoid single point of failure?
• Must be replicated to tolerate failure
• Replicas must behave consistently

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Deployability Dont Change the Message Format

• Border Gateway Protocol
• Interdomain routing protocol for the Internet
• Widely implemented and used in networks
• Three main aspects of BGP
• Protocol standard messages sent between routers
• Decision logic multi-step route selection
  process
• Policy configuration options that influence
  routing
• The key point is
• Although decision logic and policies are complex
• the protocol and message format are simple

Idea use BGP messages to tell each router how to
forward
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Phase 1 Flexible Path Selection in One AS
Before conventional use of BGP in backbone
network
eBGP
iBGP
After RCP learns routes and sends answers to
routers
eBGP
RCP
iBGP
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Phase 2 AS-Wide Path Selection and Export
Before RCP gets best iBGP routes (and IGP feed)
eBGP
RCP
iBGP
After RCP gets all eBGP routes from neighbors
eBGP
RCP
iBGP
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Phase 3 Direct Communication Between RCPs
Before RCP gets all eBGP routes from neighbors
eBGP
RCP
iBGP
After ASes exchange routes via RCP
Inter-AS Protocol
RCP
RCP
RCP
iBGP
AS 1
AS 2
AS 3
Physical peering
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RCP Architecture
Routing Control Platform (RCP)
Route Control Server (RCS)
IGP Viewer
BGP Engine
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Challenges and Contributions

• Reliability
• Problem single point of failure
• Contribution simple replication of RCP
  components
• Consistency
• Problem inconsistent decisions by replicas
• Contribution consistency without inter-replica
  protocol
• Scalability
• Problem storing all routes increases cpu/memory
  usage
• Contribution can support large ISP in one
  computer

? Building this system is feasible
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Consistency One RCP, One Partition
RCP 1
B
A

• Solution Assign all routers along the shortest
  IGP path the same exit router
• Ensures forwarding loops dont arise

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Consistency One RCP, Many Partitions
RCP 1
Partition 1
Partition 2

• Solution Only use state from routers partition
  in assigning its routes
• Ensures next hop is reachable

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Consistency Many RCPs, Many Partitions
RCP 2
RCP 1
Partition 1
Partition 2
Partition 3

• Solution RCPs receive same IGP/BGP state from
  each partition they can reach
• IGP provides complete visibility and connectivity
• RCS only acts on partition if it has complete
  state for it

?No consistency protocol needed to guarantee
consistency in steady state
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RCS Scalability

• Eliminate redundancy
• Store only a single copy of each BGP route
• Accelerate lookup
• Quickly find routers whose routes changed
• Avoid recomputation
• Compute routes once for groups of routers
• Dont recompute if relative ranking of egress
  routers unchanged

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Scalability RCS Data Structures
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Example of Egress List Operation
Ds egress list
B
C
A
C
3
7
4
3
A
4
D
B
7
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Example of Egress List Operation
Ds egress list
B
C
A
2
C
3
7
4
3
2
A
4
D
B
7
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Example of Egress List Operation
Ds egress list
B
C
A
C
3
5
7
4
3
5
A
4
D
B
7
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Example of Egress List Operation
Ds egress list
B
C
A
C
3
1
7
4
3
A
4
D
B
7
1
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Scalability Standard Computing Platform

• Implementation platform
• 3.2 GHz Pentium-4
• 8 GB memory
• Linux 2.6.5 kernel
• Workload
• Routing/topology changes in ATTs network
• RCP performance
• Memory usage less than 2GB
• Speed, BGP changes less than 40 msec
• Speed, topology changes 0.1-0.8 seconds
• System is able to keep up

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Application DDoS Blackholing

• Blackholing of denial-of-service attacks
• Preconfigure a null route on each router
• Identify address of victim (from DoS system)
• RCP assigns a null route for the destination

RCP
iBGP
Victim 1.2.3.4
attack (detected by traffic analysis)
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Application Maintenance Dry-Out

• Dry-out of traffic before maintenance
• Plan to take a router temporarily out of service
• RCP assigns routes via new egress in advance

RCP
s
d
iBGP
r
Router r about to undergo maintenance
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Application Customized Egress Selection

• Customer-controlled selection of egress points
• Customer with two data centers and many sites
• Customer wants to control the load balancing
• RCP customization, not simply closest egress

Use route via s for d
RCP
Site 1
s
d
Use route via r for d
Site 2
iBGP
r
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Conclusion

• Managing IP networks is too hard
• IP architecture not designed for management
• Complex, distributed operation of routers
• Reducing complexity in the key
• Network-wide views/objectives and direct control
• Removing control logic and state from the routers
• New architecture is feasible
• RCP is deployable, scalable, and reliable
• RCP solves important operations problems

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Future Work

• Optimization
• Real-time adaptation and offline planning
• Designing the boundary to support optimization
• Security
• Identifying unstable and suspicious BGP routes
• Incrementally deploying a more secure protocol
• Policy
• High-level specification of routing policies
• Quantifying reductions in configuration
  complexity