routing (cos 598a) today root-cause analysis.ppt

Routing (COS 598A)Today: Root-Cause Analysis
Jennifer Rexford
/~jrex/teaching/spring2005
Tuesdays/Thursdays 11:00am-12:20pm
Outline
Network troubleshooting
Motivation work troubleshooting
Investigating from the edge vs. inside
Active probing
Traceroute
Mapping IP addresses to AS numbers
Passive monitoring
Analyzing BGP update streams
Identifying location and cause of routing change
Limitations of the approach
Network Troubleshooting
“Why can’t I reach ?”
“Why is the performance bad?”
Reachability Problems: What Could be Wrong?
End-host problem
Web server down
DNS server down, or misconfigured
Forwarding-path problem
Packet filter or firewall restricting access
Mismatch in Maximum Transmission Unit (MTU)
Routing problem
User or server disconnected from
Blackhole dropping all packets
Persistent loop
Performance Problem: What Could be Wrong?
End-host problems
Overloaded Web server
Overloaded DNS server
Overloaded user machine
Forwarding-path problem
High round-trip time
Link congestion
Routing problem
Long-term routing instability
Transient disruption during convergence
Motivation for Troubleshooting
Improving performance
Detect, diagnose, and fix the problem
Pick a path through another provider
Pick a different path in any work
Establishing accountability
Enforce Service Level Agreements
Rate service providers
Characterizing the
Understand causes of performance problems
Understand challenges of troubleshooting
Troubleshooting Outside vs. Inside
Outside: work edge
Who: users and researchers, and operators troubleshooting problems outside work
Data: ping/traceroute, public feeds of BGP updates, and public measurement platforms
Challenges: inference from very limited data
Inside: from inside work
Who: operators running work
Data: SNMP, fault data, traffic measurement, route monitors, and router configuration files
Challenges: collecting and joining the data
Today
Active Probing
Pros and Cons of Active Probing
Advantages
Can run from any en