1. Experiences in Traceroute and Available Bandwidth Change Analysis
Connie Logg, Les Cottrell & Jiri Navratil
SIGCOMM’04 Workshops
September 3, 2004
Modern data intensive science such as HENP requires the ability to copy large amounts of data between collaborating sites. This in turn requires high-performance reliable end-to-end network paths and the ability to take advantage of them. End-users thus need both long-term and near real-time estimates of the network and application performance of such paths for planning, setting expectations, and trouble-shooting.
The IEPM-BW (Internet End-to-end Performance Monitoring - BandWidth) project was instigated in 2001 to meet the above needs for the BaBar HENP community. This produced a toolkit for monitoring Round Trip Times (RTT), TCP throughput (iperf), file copy throughput (bbftp, bbcp and GridFTP), traceroute and more recently lightweight cross-traffic and available bandwidth measurements (ABwE). Since then it has been extended to LHC, CDF, D0, ESnet, Grid, and high performance network Research & Education sites, about paths are now being monitored (including about 50 remote sites) and the monitoring toolkit has been installed at ten sites and is in production at three or four sites, in particular FNAL (for CMS, CDF and D0) and SLAC (for BaBar and PPDG). Each monitoring site is relatively independent and the monitoring is designed to map to the design of modern HENP tiering of sites, i.e. it is hierarchical rather than full mesh. The monitoring toolkit is installed at the site and its contact chooses the remote hosts it wishes to monitor.
Current work is in progress to analyze and visualize the traceroute meaurements and to automatically detect anomalous step down changes in bandwidth.
Partially funded by DOE/MICS Field Work Proposal on Internet End-to-end Performance Monitoring (IEPM), also supported by IUPAP

2. Motivation
High Energy Nuclear Physics (HENP) analysis requires the effective distribution of large amounts of data between collaborators world wide.
In 2001 we started development on a project (IEPM-BW) for Internet End-to-end Performance Monitoring of BandWidth) for the network paths to our collaborators
It has evolved over time from network intensive measurements (run about every 90 minutes) to light weight non-intensive measurements (run about every 3-5 minutes)

3. IEPM-BW Version 1
IEPM-BW version 1 (September 2001) performed sequential heavy weight (iperf and file transfer tests) and light weight (ping & traceroute) measurements to a few dozen collaborator nodes – it could only be run a few times a day
Concurrently an Available BandWidth Estimation (ABWE) tool was being developed by Jiri to perform light weight available bandwidth (ABW), link capacity (DBCAP), and cross traffic (XTR) estimates

4. IEPM-BW Version 2
IEPM-BW version 2 incorporated ABWE as a probing tool, and extensive comparisons were made between the heavy weight iperf and file transfer tests and the ABWE results
ABWE results tracked well with iperf and file transfer tests in many cases

5. Forward Routing changes Reverse Routing changes
Examples
New CENIC path
1000 Mbits/s
Forward Routing changes
ABWE
Iperf
back to new CENIC path
Bbftp
Iperf 1 stream
Drop to 622 Mbits/s path
Reverse Routing changes
28 days bandwidth history. During this time we can see 3 different situations caused by different routing from SLAC to CALTECH
Scatter plot graphs of Iperf versus ABW on different paths (range 20–800 Mbits/s) showing agreement of two methods
(28 days history)

6. Challenges The monitoring was very useful to us but:
Too many graphs and reports to examine manually every day
We could only run the probes a few times a day
We needed to automate what the brain does – pick out changes
Changes of concern included: route and bandwidth

7. Traceroute Analysis
Need a way to visualize traceroutes taken at regular intervals to several tens of remote hosts
Report the pathologies identified
Allow quick visual inspection for:
Multiple routes changes
Significant route changes
Pathologies
Drill down to more detailed information
Histories
Topologies
Bandwidth monitoring data

8. Display Many Routes on Single Page
One compact page per day
One row per host, one column per hour
One character per traceroute to indicate pathology or change (usually period(.) = no change)
Identify unique routes with a number
Be able to inspect the route associated with a route number
Provide for analysis of long term route evolutions
Route # at start of day, gives idea of route stability
Multiple route changes
(due to GEANT), later restored to original route
Period (.) means no change

9. Pathology Encodings Probe type: UDP or ICMP Hop does not respond (*)
End host does not respond, i.e. 30 hops (|)
Stutters (“) – hop replies more than once
Hop change only affects 4th octet (: )
Hop change but address in same AS (a)
ICMP checksum (orange)
! Annotation e.g. network unreachable, admin blocked
Multi-homed host
There are several pathologies associated with traceroutes. We needed to find a way to encode them.

10. Pathology Encodings Change but same AS No change Probe type
Change in only 4th octet
End host not pingable
Hop does not respond
Stutter
Multihomed
ICMP checksum
! Annotation (!X)

11. Navigation
traceroute to CCSVSN04.IN2P3.FR ( ), 30 hops max, 38 byte packets
1 rtr-gsr-test ( ) ms …
13 in2p3-lyon.cssi.renater.fr ( ) ms !X
#rt# firstseen lastseen route
, , , ,..., xxx.xxx
, , ,137,..., xxx.xxx
, , , ,..., xxx.xxx
, , , ,..., xxx.xxx
, , , ,...,(n/a), xxx.xxx
, , , ,..., xxx.xxx
, , , ,..., xxx.xxx
, , ,(n/a),..., xxx.xxx
, , , ,(n/a),..., xxx.xxx

12. History Channel

13. AS’ information

14. Esnet-LosNettos segment in the path
Changes in network topology (BGP) can result
in dramatic changes in performance
Hour
Samples of traceroute trees generated from the table
Los-Nettos (100Mbps)
Remote host
Snapshot of traceroute summary table
Notes:
1. Caltech misrouted via Los-Nettos 100Mbps commercial net 14:00-17:00
2. ESnet/GEANT working on routes from 2:00 to 14:00
3. A previous occurrence went un-noticed for 2 months
4. Next step is to auto detect and notify
Drop in performance
(From original path: SLAC-CENIC-Caltech
to SLAC-Esnet-LosNettos (100Mbps) -Caltech )
Back to original path
Dynamic BW capacity (DBC)
Changes detected by
IEPM-Iperf and AbWE
Mbits/s
Available BW = (DBC-XT)
Cross-traffic (XT)
Esnet-LosNettos segment in the path
(100 Mbits/s)
ABwE measurement one/minute for 24 hours Thurs Oct 9 9:00am to Fri Oct 10 9:01am

15. Data Display Many different and useful ways to look at traceroute data
Output from traceroute command
Tabular format: facilitates comparisions
#date # time #hops epoch rtno node route
08/31/ :13: node1.cesnet.cz , ,..., , ,..., xxx.xxx
08/31/ :23: node1.cesnet.cz , ,..., , ,..., xxx.xxx
08/31/ :33: node1.cesnet.cz , ,..., , ,..., xxx.xxx
Topology maps

16. Data Display
Historical list of routes (route number, first seen date, last seen date, hops)
#rt# firstseen lastseen route
, , , ,..., xxx.xxx
, , ,137,..., xxx.xxx
, , , ,..., xxx.xxx
, , , ,..., xxx.xxx
, , , ,...,(n/a), xxx.xxx
, , , ,..., xxx.xxx
, , , ,..., xxx.xxx
, , ,(n/a),..., xxx.xxx
, , , ,(n/a),..., xxx.xxx

17. Summary We are quite happy with our traceroute analysis
One page per day to eyeball for route changes
Links provided for ease of further examination
Do not alert on traceroute changes, but traceroute information is integrated with Bandwidth Change Analysis
IEPM-BW in Action

18. Bandwidth Change Analysis
Purpose is to generate “alerts” about “major” drops in available bandwidth and/or link capacity which may be impacting our physics analysis production work
Inspired by “Plateau Algorithm” for analyzing ping data from McGregor and Braun
The implementation is described in the paper so I am not going to go over it here

19. Overview
We currently feed a weeks worth of data into it for developmental and verification purposes
The actual implementation processes that weeks worth of data in a sliding window of currently about 24 hours
A 1st level “alert” is generated when there is a period of depressed bandwidth for about 3 hours. Our threshold of depression is currently 40%
There is one web page that displays an analysis overview with links to more details

20. Gigabit Link Examples

21. Kilobit Link Example
Today’s Page

22. Challenges Diurnal Variations Capacity Available bandwidth RTT
X traffic

23. Challenges Unusual variations Trigger buffer length 10 points
In this case, we wanted to know that this was happening
Trigger buffer length 30 points

24. Considerations
From the performance monitoring perspective of managing a production network, we are primarily concerned about pathologies that interfere with the production process
We are not really interested in the minor ebb and flow of network traffic
We are not interested in monitoring the entire “Grid”
We are interested in monitoring what are users are “seeing”

25. Challenges
There are many algorithms which may be useful in analyzing data for various types of variations with which we may not be concerned
Developing code for this is challenging and complex, but can be done.
Problem: CPU power and “elapsed” time to analyze monitoring data with all these analysis tools is impractical – most of us cannot afford supercomputers or farms to do it
Analysis and identification of “events” must be timely

26. Solutions
Quick first level trigger analysis which can be done frequently to check for “events”
Provide web page for looking at general health and first level trigger occurrences
Can also invoke immediate but synchronized more extensive tests to verify drops
Input event data (and longer term data) into more sophisticated analysis to filter for serious “alert”s
Save event signatures for future reference

27. IEPM-BW Future
IEPM-BW Version 3 is being architected to facilitate frequent light available bandwidth and link capacity measurements
Will use SQL database to manage the probe, monitoring host, and target host specifications as well as the probe data and analysis results
Frequent lightweight first trigger level change analysis

28. Long Term
Facility for scheduling on demand and automatic heavyweight bandwidth tests in response to triggers
Automatically feed results into more complex analysis code to filter only for “real” alerts
Distributed self contained independent monitoring systems
Working on a technique to encode bandwidth variation signatures (such as diurnal variations)

29. References
ABWE: A Practical Approach to Available Bandwidth Estimation, Jiri Navratil and Les Cottrell
Automated Event Detection for Active Measurement Systems, A. J. McGregor and H-W. Braun, Passive and Active Measurements 2001.
Overview of IEPM-BW Bandwidth Testing of Bulk Data Transfer, Les Cottrell and Connie Logg
Experiences and Results from a New High Performance Network and Application Monitoring Toolkit, Les Cottrell, Connie Logg, and I-Heng Mei
Correlating Internet Performance Changes and Route Changes to assist in Trouble-Shooting from an End-User Perspective, Connie Logg, Jiri Navratil, and Les Cottrell
Miscellaneous, SLAC

30. Future - continues Further develop Bandwidth Change Analysis
Now have 1st level trigger mechanism
Develop more extensive analysis to analyze identified events
Develop algorithms to automatically conduct other tests integrate those results into further trigger analysis

31. IEPM-BW Version 3 Architecture changes
SQL data base for host specifications, probe tool specifications, probe scheduling mechanism, analysis results, knowledge base
Scheduling mechanisms for lightweight vs heavyweight probes
Distributed monitoring and remote data retrieval for “grid” analysis
Change analysis (route and bandwidth) and alerts