Investigation of Global Network Routing Behavior

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Investigation of GlobalNetwork Routing Behavior

• BJ Premore
• Dartmouth College
• Prof. David Nicol, Advisor
• December 8, 2000
• In collaboration with
• Jim Cowie, Renesys Corporation
• Tim Griffin, ATT Labs-Research
• Andy Ogielski, Renesys Corporation
• and several other colleagues

2
Overview

• Objectives
• better understand inter-domain routing dynamics
• explore impact of implementation tradeoffs
• explore extensions before deployment
• provide a useful tool for researchers
• Implementation
• simulation architecture
• BGP functionality
• validation
• Research Applications
• convergence (ongoing)
• security (ongoing)
• timing, policy interaction, proposed extensions,
  etc.

3
Overview

• Objectives
• better understand inter-domain routing dynamics
• explore impact of implementation tradeoffs
• explore extensions before deployment
• provide a useful tool for researchers
• Implementation
• simulation architecture
• BGP functionality
• validation
• Research Applications
• convergence (ongoing)
• security (ongoing)
• timing, policy interaction, proposed extensions,
  etc.

4
Simulation Architecture
DML Domain Modeling Language - model
configuration
SSFNet SSF Network Models - compositional
approach to large network design - not
independent
SSF Scalable Simulation Framework - a modern
standard for discrete-event simulation of
large, complex systems - multiple
implementations - the engine under the hood
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Simulation Layers
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Why Another Simulator?

• Fully Integrated Network Environment
• control over more than just BGP
• eg TCP/IP, traffic, router link hardware
• Scalability
• designed to handle large, complex simulations
• tens of thousands of multi-protocol nodes
• Design Trade-off Toggles
• eg tie-breaking in route selection
• eg apply minAdver timer to withdrawals
• Explore Impact of New Functionality
• before it goes live!
• eg MPLS protocol extensions

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Pros and Cons

• We cant
• expect to model real-world routers perfectly with
  every detail
• We can
• capture the most important characteristics
• change and tweak the protocol
• explore consequences of fundamental design of BGP
• explore proposed and novel protocol extensions
• evaluate and analyze collective behavior on a
  large-scale

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SSFNet Layer
DML configurations
Model Instances
configure
Network Components as Java Classes
SSFNet
enhances
Simulator Implementations
CSSF
Raceway
DaSSF
implements
implements
implements
C
C
Java
SSF standard
Simulator API
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Example SSFNet Components
protocols
IP
TCP
Sockets
FTP
logical containers
BGP
HTTP
OSPF
Net
protocol graph
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SSF.OS.BGP

• Based on RFCs
• RFC 1771 BGP-4 and latest drafts
• RFC compliant implementation
• Includes some RFC-specified extensions (Route
  Reflection)
• Has features similar to those used by vendors
  (policy-based filtering)

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SSF.OS.BGP4 Functionality

• Finite state machine, timers, RIB
• TCP transport
• Peering exterior and interior
• Route reflection
• Messages and path attributes
• Policy
• filter based on path attribute
• attribute modification
• Monitoring of protocol operation
• gather stats on practically any event of interest

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Package SSF.OS.BGP4 Organization
BGPSession
PeerEntry
PeerEntry
RIBIn
LocRIB
RIBOut
RIBOut
RIBIn
Policy Rule (inbound)
Timers ConnRetry KeepAlive Hold MinAdver
Policy Rule (outbound)
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Validation Methodology

• No standards, create our own suite
• Basic behavior in simple topologies
• Peering session maintenance (Hold KeepAlive
  timer operation)
• Route advertisement and withdrawal
• Route selection
• Reflection
• Internal BGP
• General behavior in complex topologies
• End-to-end data delivery
• Exercises basic behaviors as well
• Policy testing
• Converging and non-converging gadgets Griffin
  1999

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Example Route Reflection Validation Test Topology
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Another Test Topology
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Large Network Example
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Example With Monitoring
Filters
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DML Example
host id 1 interface id 1 router
id 2 interface idrange from 1 to 4
link attach 1(1) attach 2(1)
1
2
1
1
2
3
4
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DML Adding Protocols
router graph ProtocolSession
name bgp use SSF.OS.BGP4.BGPSession
ProtocolSession name ospf use
SSF.OS.OSPF.sOSPF ProtocolSession
name tcp use SSF.OS.TCP.tcpSessionMaster
ProtocolSession name ip
use SSF.OS.IP
BGP
OSPF
TCP
IP
protocol graph
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Overview

• Objectives
• better understand inter-domain routing dynamics
• explore impact of implementation tradeoffs
• explore extensions before deployment
• provide a useful tool for researchers
• Implementation
• simulation architecture
• BGP functionality
• validation
• Research Applications
• convergence (ongoing)
• security (ongoing)
• timing, policy interaction, proposed extensions,
  etc.

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Interesting Possibilities

• Better value for MinAdver timer?
• Improved route flap dampening?
• Policy studies
• How do various configurations affect convergence?
• Test effects of policy changes before deployment
• EGP-IGP interaction studies
• Are there instability side-effects?
• Is it safe to convert between different cost
  metrics?
• MPLS
• Will it have any unexpected effects on routing?
• Security studies

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A Security Study

• Black Holes
• How many networks can/will be included?
• parameters
• severity of misconfiguration or maliciousness
• number of misbehaving routers
• location of misbehaving routers
• Other Questions
• What is the impact of SBGP on routing efficiency?
• Can attacks and misconfigurations be detected?
• How can we speed up convergence after an attack?

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A Convergence Study

• Goals
• build upon previous work
• Labovitz, Ahuja, Bose Jahanian 2000
• what factors contribute to observed dynamic
  behaviors?
• isolate contributions of different parameters
• policy, topology, iBGP, timers, etc.
• make recommendations for implementations
  (eventually)
• what changes can alleviate impact of various
  factors?

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A Convergence Study

• Model Parameters
• topology N ASes each with just 1 router
• shape line, loop, wheel, meshes, grid
• size vary N from 2 to 100
• policy
• permit all or typical customer/provider/peer
• link delay
• all equal or random
• Advertise, Withdraw, Wait and Watch
• Wait for system to reach stable state, then
• Designated AS advertises a bogus destination to
  everyone else
• Wait for system to reach a stable state again,
  then
• Designated AS tells everyone that the bogus route
  is not reachable through it any more
• Wait for system to reach a stable state again

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Simple Topologies
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Line Experiment
fixed or random link delays
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Loop Experiment
fixed link delays
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Wheel Experiment
fixed link delays
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IBGP Full Mesh Experiment
fixed link delays
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EBGP Full Mesh Experiment
fixed link delay
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Grid Experiment
fixed link delay, width10, no policy
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Preliminary Observations

• Convergence time related to number of alternate
  paths a router sees
• policy helps reduce
• Agreement with previous results
• full mesh experiments in particular
• Full external mesh still the most interesting
• how many alternate paths are actually seen
  depends a lot on timing
• using random link delays reduced convergence time

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Coming Soon

• Functionality
• aggregation
• route flap dampening
• communities
• confederations
• and more ...
• Experiments
• look for better timer values
• how does policy affect convergence?
• can we improve route flap dampening?
• test extensions and other proposed modifications
• and more

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For Further Information

• SSF/Raceway and SSFNet
• http//www.ssfnet.org/
• SSF.OS.BGP4
• http//www.cs.dartmouth.edu/beej/research/bgp/jav
  a/
• (or follow link from www.ssfnet.org)

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This sample DML code configures an AS with a
single router running BGP. It performs explicit
configuration of all BGP attributes. It is taken
from the goodgadget validation test.
(continued next page)
Net id 1 AS_status boundary
router id 1 graph
ProtocolSession name bgp use
SSF.OS.BGP4.BGPSession autoconfig
false connretry_time 120
min_as_orig_time 15 reflector false
neighbor as 0 address 1(1)
use_return_address 1(1) hold_time 90
keep_alive_time 30 min_adver_time 30
infilter give low priority to routes learned
from 0 clause
precedence 1 predicate
action primary
permit atom attribute
local_pref type set value 80

outfilter _extends .filters.permit_all

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neighbor as 2 address
1(2) use_return_address 1(2)
hold_time 90 keep_alive_time 30 min_adver_time
30 infilter give high priority to
routes learned from 2 clause
precedence 1 predicate
action
primary permit atom
attribute local_pref type set value 100

outfilter _extends .filters.permit_all
neighbor as
3 address 1(2) use_return_address 1(3)
hold_time 90 keep_alive_time 30
min_adver_time 30 infilter deny
all routes learned from 3 clause
precedence 1 predicate action primary deny
outfilter
_extends .filters.permit_all
ProtocolSession name socket use
SSF.OS.Socket.socketMaster
ProtocolSession name tcp use
SSF.OS.TCP.tcpSessionMaster
ProtocolSession name ip use SSF.OS.IP
interface idrange from 0 to 3
host id 101 _extends .basic_host
link attach 1(0) attach 101(0) delay 0.001